Update At 3:50 PM: A Squall Line With A History Of Wind Damage Is Moving Across Eastern Kentucky Toward The VA-KY Stateline. Expected Arrival Is Around 5:00-5:30 PM ( give or take 15 minutes ).
The squall line will reach Cumberland Gap by around 4:15 to 4:30 PM and the Norton-Wise area between 5:00 & 5:30 PM.
Previous Overnight Forecast
ALERT For A Dramatic Weather Change From Late This Afternoon Into Wednesday Morning. A Squall Line Of Heavy Rain-Possible Storms Will Give Way To A Wind Shift With ROARING Evening Winds And A Sharp Drop In Temperatures Between 10 PM and Wednesday AM. Lingering Rain Changing To Snow ( A Dusting Up To 2″ Possible On Upslope Side of Mountains – NW Flow ).
*A large change in air pressure will drive a strong cold front across the mountains by late today into Wednesday AM. A squall line of heavy rain-possible thunderstorms will reach the VA-KY stateline by around 5:00 PM, followed by ROARING evening winds as colder air begins to pour into the mountains. Lingering rain showers will change to snow showers, with potential for light accumulations and icy-hazardous conditions ( underfoot and on some roads ) to form between 10 PM Tuesday and sunrise Wednesday. Although snowfall amounts will be light, the sharp temperature drop could form black ice and eventually allow snow showers to stick at the higher elevations ( especially ). Porches-decks-walks, etc…should be checked before stepping out onto them by Wednesday AM.
Overnight Into Tuesday Morning
Mostly clear. Large vertical temperature spread forming between colder valleys and milder middle-upper elevation mountain ridges-plateaus. Winds SSE-SW at 5-15 mph, with higher gusts, on mid-upper elevation ridges. Temperatures varying from 20s in colder valleys to upper 30s to mid 40s on exposed mountain ridges and plateaus. Wind chills in the 30s to lower 40s on mountain ridges.
Mid-Morning Through Late Afternoon
Increasing clouds. Becoming windy. A chance for showers by early afternoon. A squall line of heavy rain & possible thunderstorms by late ( around 5 PM give or take an hour ). SSW-SW winds increasing to 15-25 mph, with higher gusts, especially gusty on mid-upper elevation mountain ridges & plateaus. Temperatures varying from the 40s to around 50 degrees at highest elevations in the High Knob Massif to the lower-middle 60s in milder locations.
*Although the risk for severe thunderstorms will be locally low, a very dynamic weather system and strong cold front will create an environment where this will need to be closely followed as one or more bands ( or a main squall line ) of showers-thunderstorms will be approaching the mountains from the west & southwest by late afternoon into this evening. Damaging winds are the greatest threat, outside of always dangerous lightning, along with downpours of heavy rainfall upon an already wet ground.
Late Afternoon Into Wednesday Morning
Showers & thunderstorms. Locally heavy rainfall. Some storms may be strong with a possible squall line timed to reach the VA-KY stateline by 5 PM ( give or take 1-Hour ). Winds shifting WNW-NW at 10-20 mph, with gusts of 30- 40+ mph along and behind the cold front. Turning much colder with a sharp temperature plunge from around 10:00 PM into the overnight period. Rain showers changing to snow showers. Temperatures plunging into the low-mid 20s by morning, with low-mid 10s at highest elevations in the High Knob Massif ( milder south toward the Tri-Cities ). Wind chills plunging into single digits & 10s ( locally lower in gusts atop the High Knob Massif ) overnight into the AM.
A wet snow potential, with several inches possible, continues to be watched for the late Thursday into Friday AM period ( March 3-4 ). Stay tuned for updates.
Weather Discussion ( Feb 29 – March 1 )
My Afternoon Update
The focus this afternoon is on a squall line of strong-severe thunderstorms, with a history of wind damage, moving into the Kentucky foothills near the mountains.
Some loud thunder & lightning in Clintwood at 5:11 PM
A 61 mph wind gust reported on Flatwoods Mountain, adjacent to Pine Mountain, near the Virginia-Kentucky stateline at 5:15 PM.
Blinding rain and strong winds in Clintwood at 5:22 PM
It has gotten dark like night with heavy rain and wind at 5:25 PM in Clintwood ( now into Norton-Wise ). Booming thunder with a lightning strike at 5:29 PM.
Another BOOM of thunder with vivid lightning at 5:32 PM.
The line is weakening across the High Knob Massif area.
Wind damage has occurred in London, Ky., including buildings, trees, and at least 1 injury, with passage of this squall line.
Warnings have expired in eastern Kentucky, currently, but the line continues to have a mini-waves indicative of strong winds.
This warning is no longer in effect.
Temperatures remain chilly atop the high mountains this afternoon with middle 40s. This means limited instability with dewpoints in mid 40s to lower 50s across the area.
However, momentum transfer of strong winds aloft will remain possible. ROARING winds will overspread the area tonight behind the cold front.
My Overnight Discussion
A simply lovely close to the month of February, and also Meteorological Winter, has given way to a cold and frosty night amid mountain valleys verses gusty conditions and “milder” temperatures atop mid-upper elevation ridges.
It was 30.0 degrees exactly at my official Clintwood station at Midnight, with 31 degrees in Jonesville and Sandlick, verses a relatively balmy ( by contrast ) 46 degrees ( really 44 with the warm bias ) at Lonesome Pine Airport in Wise.
Colder mountain valleys were already in the 20s at Midnight, such that this large vertical temperature spread will increase into the overnight between valleys that remain decoupled ( detached from winds above ) from the flow field of the atmosphere and breezy-gusty mountain ridges & plateaus.
The main focus of this forecast period is on a dramatic weather change that will be developing between late this afternoon and Wednesday morning, with high-resolution models of the NAM group now coming into line with the more aggressive forecast of the European Model.
Note too the 58+ mph low-level jet being shown along the front where isobars bend into a trough above over SE Kentucky. While winds will be gusty before the front, all locations will tend to develop ROARING winds into evening as much of that momentum mixes downward toward the surface along with increasing cross-barrier flow as barometric pressure begins adjusting across the Appalachian chain ( large pressure falls then rises tonight ) from northwest to southeast. A classic strong wind setting for a time later today into tonight. Any squall line with heavy rain will be amid this setting ( toward 5:00 PM, give or take an hour ). A squall line also implying that the heavy rain will tend to be limited in time ( good news for wet ground, yet downpours must always be respected in case they might linger over any given place for a little longer in time ).
To illustrate the change, the NAM Model predicts the 7:00 PM temp over Wise to be 48 degrees up at the summit level of the High Knob Massif. By 7:00 AM Wednesday ( below ) the air temperatures has plunged to 12 degrees at the High Knob summit ( a 36 degree drop which can be translated downward to Norton-Wise to mean temps that plunge from 50s to around 60 degrees this afternoon to 20-23 degrees by Wednesday morning ). This temperature drop is also forecast by the European Model ( increasing confidence ).
Winds continue to be gusty, especially along mid-upper elevation ridges-plateaus, into Wednesday morning such that feels-like conditions will truly be dramatic relative to temperatures experienced for a time today.
Any time there is such a dramatic air mass change the risk for strong to locally severe thunderstorms often must be respected ( especially entering Meteorological Spring ).
The Cumberland Mountains remain on the fringe with a marginal risk being maintained for severe storms. The greatest severe threats ( as I had already noted earlier ) being for the possibility of damaging winds.
Kentucky is at the center of the potential for at least brief spin-ups ( tornadoes ) today, west of the mountains, and it will be this activity that will need watching as it pushes eastward to the mountains during the afternoon.
The 1:00 AM run of the HRRR Model has the squall line getting close to the Virginia-Kentucky border, west of Cumberland Gap, around 4:00 PM. So I have adjusted my timing for Norton-Wise upward to 5:00 PM ( give or take an hour ). This timing may still change and have to be updated later.
Stay tuned to NOAA Weather Radio for possible watches and/or warnings that might be needed today.
ALERT For Strong SW Winds Tonight Into Monday Morning Is In Effect For The Cumberland Mountains
SW winds will continue to roar across the mountain area in advance of a cold front with rain showers. The strongest winds will occur at mid-upper elevations, above 2000 feet, and with mountain waves northeast of the High Knob Massif and Black Mountain into portions of the Russell Fork basin.
A Risk For Strong-Severe Thunderstorms Will Become Possible By Late Tuesday, Especially West-Southwest Of The Cumberland Mountains.
Overnight Into This Morning
Increasing clouds with showers developing by the predawn to sunrise period. Windy. SW winds 15-30 mph, with gusts of 35-40+ mph. Temperatures varying from low-mid 40s at highest elevations in the High Knob Massif to widespread readings in the 50s, then dropping around sunrise into mid morning with onset of showers. Wind chills in the 30s and 40s on exposed mid-upper elevation ridges-plateaus.
Mid-Morning Through Monday Afternoon
Decreasing clouds with mostly sunny conditions developing into afternoon. Winds becoming WNW-WSW & decreasing to 5-10 mph. Mid-morning temperatures in the 30s and 40s rising into the low-mid 40s to low-mid 50s ( coolest at the highest elevations & milder south toward the Tri-Cities ).
Tonight Into Tuesday Morning
Mostly clear. Large vertical temperature spread forming between colder valleys and milder mid-upper elevation mountain ridges-plateaus. Winds SSE-SSW at 5-15 mph, with higher gusts, on mid-upper elevation ridges. Temps varying from 20s in colder valleys to the upper 30s to mid 40s on exposed mountain ridges-plateaus. Wind chills in the 30s to lower 40s.
While rain may change to snow showers at mid-upper elevations into Wednesday morning ( any accumulations are currently most likely at highest elevations ), a more important storm system will present a wintry potential Thursday Into Friday ( March 3-4 ). Please stay tuned for updates on both of these systems.
Weather Discussion ( February 27-29 )
My Afternoon Update
Following morning showers, clouds, and a dip into the 30s and 40s this afternoon has been ideal with beautiful blue skies and decreasing winds.
Afternoon temperatures varying from chilly 40s atop the High Knob Massif to the mid-upper 50s in Norton-Wise and adjacent plateau-ridge communities.
The main focus of this update being on the latest Day 2 outlook from the Storm Prediction Center where, as I had expected, there have been some modifications.
This will be a very dynamic system and could again feature a setting that goes from heavy rain, with thunder, to snow as temperatures plunge behind the cold front. Any sticking snow of importance continues to look like it will be within upper elevations around or above 3000 to 3500 feet ( even there it will be light if cold air does not catch up to the back side of the main moisture field ). I will update that tonight.
As is typically the case here in the mountains at this time of year, marginal dewpoints & low-level instability are limiting factors for severe thunderstorms verses much better ( stronger ) dynamics. Strong-severe thunderstorms can not be ruled out, but the latest marginal risk does look ( currently ) to be most appropriate.
There will be a band, or bands, of heavy rain with embedded thunderstorms along & ahead of the strong cold front, with models trying to figure out where it will be. The latest run of the European Model places the main band right over the Virginia-Kentucky border counties. This will also need updating later tonight.
The main weather focus Sunday evening into this early overnight period of Monday is ROARING winds, which I have put an alert out for and noted back on Friday Night.
SW wind gusts of 30 to 50 mph have been common across the area this evening into the overnight. ROARING winds.
Wind speeds began increasing at upper elevations during early afternoon, with downward mixing and lowering of strong and gusty winds into the evening.
Sunday afternoon temperatures varied widely from the 40s over lingering snow on northern slopes in upper elevations of the High Knob Massif ( with colder wind chills ) to a mild 64 degrees on downsloping winds at Clintwood 1 W.
Temperatures reached mid-upper 50s in the Norton-Wise area.
The timing and pulsating nature of ROARING winds at Clintwood 1 W are characteristic of past SW flow events that have produced mountain waves NNE-NE of the High Knob Massif and Tennessee Valley Divide.
It if were daytime these waves would show up much better with increasing moisture. Tonight there is only visual indications of their presence on infrared satellite imagery. NNE-NE of the High Knob Massif-Black Mountain corridor, in particular, is a locally known and well documented past generation zone for waves which occasionally do reach into lower elevations.
*Other indicators of these waves are relatively light winds in places like Jonesville & Duffield verses Pound-Clintwood during the same time, with downward mixing of strong and ROARING winds into Pound-Clintwood.
All this atmospheric energy will dissipate quickly following a line of showers along a cold front which arrives into the predawn-sunrise period, with a wind shift and decreasing speeds as skies become mostly sunny into this afternoon.
Until then, batten down the hatches!
This remains a very active pattern so the lull will be brief.
A more important storm system and cold front will ramp winds back up across the mountains late Tuesday into the Tuesday Night-Wednesday Morning period as a band of rain, with possible thunder, moves into the area.
A 200+ knot jet streak will be moving across the region during Tuesday Night into Wednesday Morning. There will be significant speed shear, and enough directional shear, for mesocyclonic cells to develop along and in advance of the cold front and a lobe of energy ( 500 MB vorticity ) in mid-levels of the atmosphere.
Observe how the synoptic-scale spin ( below ) shows up well in the atmosphere. The alignment of upper dynamics, with the left front exit region of this potent 200+ knot jet streak & differential positive vorticity advection associated with this mid-level energy, will be important as to how the risk for severe thunderstorms unfolds. Stay tuned for updates.
The Storm Prediction Center has already placed the area within a large slight risk region for severe thunderstorms, with later modifications being possible to likely.
The precise evolution of the convection remains uncertain but powerful upper level dynamics ( as I noted above via a few of numerous ingredients ) mandates that this situation be closely following as the main risk of any severe storms develops locally by Tuesday Night.
A period of partly to mostly clear evening skies Friday will give way to mostly cloudy conditions overnight into the sunrise to mid-morning period on Saturday ( a few more flurries can not be ruled out, especially in upslope sites ).
Expect light valley winds and W-WNW winds of 5-15 mph, with higher gusts, along mid-upper elevation mountain ridges & exposed plateaus. Temperatures will vary from teens to mid-upper 20s across most of the area.
Clouds begin breaking up for a longer time period during the morning, with partly to mostly sunny afternoon skies expected to give way to a cold and mostly clear night.
Expect Saturday afternoon temperatures to vary from 30 to 35 degrees over snow along high crest lines and north slope locations in the High Knob Massif to the lower-middle 40s, with a little milder conditions lee of the mountains toward river valleys of the Clinch, Powell, Holston and Tri-Cities.
Saturday night will feature an increasing vertical temp spread between mountain ridges and valleys, with SW to WSW winds of 10-20 mph, and higher gusts, along mid to upper elevation mountain ridges & exposed plateaus.
This will cause temperatures to tend to rise at the highest elevations from late Saturday Night into Sunday Morning. In contrast, valleys with light-calm winds will drop such that temperature spreads will vary from 10s to low 20s in colder valleys to 30s along exposed mountain ridges.
An ALERT for strong & gusty winds may be needed for middle to upper elevations by late Sunday into Sunday Night as the pressure gradient tightens along the Cumberland Mountains in advance of the next weather system.
The day begins with mostly clear skies and a relatively large temperature spread between valleys sheltered from gusty SW-WSW winds and exposed locations & mountain ridges. Although deep valleys will have colder air temps, wind chills along high ridges will make it feel just as cold.
Mostly sunny skies are currently expected with a large temp spread between upper and lower elevations. A bias toward a little cooler valley conditions will also exist for locations along and southwest of the High Knob Massif & Tennessee Valley Divide, where rising air will hold PM temperatures lower than with sinking on SW flow into lower elevations across the Russell Fork & Levisa Fork basins.
Specifically, afternoon temperatures will vary from the lower-middle 40s over snow cover at upper elevations & northern slopes in the High Knob Massif to the middle-upper 50s ( 60+ may occur in some downslope locales ). Actual “feels-like” conditions will be more extreme with wind chills making the afternoon feel like 20s to mid 30s for those who might dare to visit the High Knob Lookout.
Late Sunday into early Monday will feature increasing winds & clouds with a chance for developing rain showers. SW-WSW winds of 20-40+ mph will become possible across middle-upper elevation mountain ridges & plateaus.
Weather Discussion ( February 26+ )
Some late PM brightening of cold, cloudy conditions helped to illuminate widespread snow cover across the High Knob Massif, and set the stage for a beautiful and colorful sunset.
This was a day featuring prolific mountain waves on NW flow, with NASA visible imagery offering some nice views.
There is little doubt where the true mountains begin, with waves popping out from the Cumberland Mountain Overthrust Block and Pine Mountain southeastwards.
Some instability became superimposed on the NW flow into the afternoon, with “bumpy” clouds over much of Scott County along and lee of the High Knob Massif amid turbulent flow.
Looking ahead, a volatile pattern will open the first week of March with up-down temperature swings and more periods featuring strong winds, rain, and snow.
As I have already highlighted, the time with gushing whitewater draining from the High Knob Massif is a testimony to winter storminess already experienced.
This latest storm system pushing total precipitation into the 25.00″ to 30.00″ range for upper elevations in the High Knob Massif since December 1.
Reference Winter Majesty In High Knob Massif for totals measured before this latest major storm dropped an additional 2.50″ to 3.00″ of precipitation on the massif area ( 2.44″ being measured on the northern base of the massif at the City of Norton Water Plant ).
As highlighted in my 022016 Extended Outlook, the big picture will feature a prolonged negative trend to the Arctic Oscillation coupled with a positive Pacific North American oscillation.
This will maintain a general western USA ridge and eastern USA trough pattern in the mean, with tendency for colder than average conditions ( in the mean ). Radical up-down temperature swings will also remain likely in early days during March ( with perhaps a more stable cold pattern arising later…still too early to tell about the stability ).
While the mean western USA ridge & eastern USA trough pattern is very clearly seen on the MEAN of the 51-Member European Ensembles, there is a potential for an Omega type of blocking setting toward DAYS 7-10 ( featuring ridging centered more on the Rockies-western Plains ).
To be honest, the upcoming pattern will be complex and greatly complicated by waves in the Polar and Sub-tropical Jet Streams that will at times have the potential to phase. Any phasing could alter the upper air configuration and skew it away from the MEAN shown.
Initial focus this coming week will be on a couple of potentially major storm systems. The first one of note arises by Tuesday-Wednesday ( March 1-2 above ).
The next potential storm ( below ) will also be a concern with Gulf of Mexico moisture connection yet again.
Tracks and intensities on these remain to be determined, but clearly the stage is being set via the upper pattern and embedded waves in the Polar & Sub-tropical Jets for more storminess in coming days. These will be the focus of future forecasts, so stay tuned for updates.
ALERT For Accumulating Snow Overnight Into This Morning Along The Upslope Side Of The Mountains. Caution For Hazardous Road Conditions Along and North of High Knob Massif-Tennessee Valley Divide.
A period of increased low-level moisture will develop overnight with snow showers and local squalls increasing along the upslope side of the mountains ( with respect to NW winds ). At 11:00 PM a burst of snow had moved through Breaks Interstate Park.
Additional new accumulations of 0.5″ to 2″ are expected at lower and middle elevations, with 2″ to 3″ within upper elevations of the High Knob Massif. Little to no accumulation, as has been expected, will occur along the downslope side of the mountains ( this ALERT has always been posted for the upslope side of the mountains with respect to NW winds ).
Overnight Into Mid-Morning Friday
Snow showers & flurries. Snow may be heavy at times in the overnight-sunrise period. W to NW winds 10-20 mph, with higher gusts. Temperatures varying from the low-mid 10s at highest elevations to the mid-upper 20s ( milder at lower elevations toward the Tri-Cities ). Wind chill factors varying from single digits below & above zero at the upper elevations to the 10s to lower 20s. Blowing snow, with additional rime formation, at highest elevations.
Mid-Morning Through This Afternoon
Mostly cloudy & cold. Chance of flurries or snow showers. W-NW winds 5-15 mph, with higher gusts. Temperatures varying from lower 20s to lower-mid 30s ( coldest at the highest elevations ). Wind chills in the 10s & 20s, except some single digits at highest elevations.
Tonight Into Saturday Morning
Mostly cloudy & cold. Chance of flurries. W-WSW winds at 5-15 mph, with higher gusts, along mid to upper elevation mountain ridges. Temperatures mostly in the 20s, varying from around 20 degrees at highest elevation to around 30 degrees. Wind chills in the 10s & 20s, except some single digits along upper elevation mountain ridges.
Weather Discussion ( February 25-26 )
My Afternoon Discussion
Its been a cold day across the mountain area with 4:00 PM temperatures varying from a bitter 20 degrees atop Eagle Knob of the High Knob Massif to 31 degrees ( 30.6 ) at the City of Norton Water Plant ( reported by Joe Carter ).
This followed an overnight that featured periods of heavy snow from the High Knob Massif northward into parts of Wise and Dickenson counties.
A general 0.5″ to 2.0″+ of new snow accumulated, enough to force Wise County to close schools on this TGIF ( Feb 26 ). No new snow accumulated in many downslope places, as well as in spots that happened to miss the overnight snowstreaks and squalls along upslope sides of the mountains ( e.g., only a trace in Grundy ).
Total snowfall during this event had reached 4.0″ in the High Chaparral community of the High Knob Massif up to 9:43 AM this morning. Look for scenes from the summit level and main crest zone coming later.
Snowfall was generally less in Norton-Wise and less still toward Pound and Clintwood where, with melting Thursday, some places barely had a dusting ( that missed overnight snow squalls ).
In general; however, it was clearly an elevation biased snow event featuring snowfall ranges along the upslope side of the mountains which varied from 1″ to 6″+ ( during the entire Feb 24-26 period ).
My Overnight Discussion
Light snow has been increasing, mixed with sleet in valleys, over Dickenson and Buchanan counties during the evening with a burst of heavier snow recently moving through the Breaks Interstate Park area. This marks the beginning of a return of better low-level moisture.
When forecasting Great Lake connected NW upslope flow, from this far away from the moisture source, it is all about being PATIENT and giving the moisture time to make the long trek downstream into the mountains.
Nothing had changed dramatically in the flow, as was expected, with a mostly mid-continental flow into the mountain area at 7:00 PM. That supported light snow.
Overnight models continue to show the flow shifting to off Lake Michigan into the mountains for a period of time from the overnight-predawn into mid-morning Friday. This will be the period for accumulating snow ( i.e., Midnight to Mid-Morning on Friday will be the best time ).
The only change in my forecast has been to reduce snowfall amounts slightly due to sleet mixing in at lower elevations this evening within the Russell For Basin.
With Great Lake supported upslope flow upstream radars may not look very active, but echoes increase along the mountains as moisture reaches the lifting zone.
Streamers are clearly visible coming off Lake Michigan, indicating that moisture is being transported off the open Lake. Little is seen beyond the immediate inland Lake zone in Michigan-Indiana until the air reaches the Appalachian foothills in Kentucky & western West Virginia ( with additional lifting then into the Alleghenies and Cumberland mountains ).
One reason I have not backed off on overnight snowfall is that there is also to be a 10 degree temperature drop at the summit level of the High Knob Massif, and in many places, with arrival of the 850 MB thermal MIN and coldest air that will help promote increased dendritic crystal growth at a lower altitude in the atmosphere ( even though the most prime growth zone of -12 to -17 C is not quite going to be reached there should still be some decent crystal growth ).
So time will tell. One of the problems in dealing with Great Lake moisture is that only a few degrees of change on the compass can make for large changes downstream at distances of 400 air miles, and models have a difficult time resolving these streams of richer low-level moisture with respect to where they will exactly form and reach over time.
*The distance from the end of Lake Michigan to the High Knob Massif is approximately 400 air miles.
Whitewater continues to gush as part of a prolonged period with significant flow on the dozens of steep creeks draining the High Knob Massif ( a testimony to February and Winter wetness in this 2015-16 season ).
ALERT For Accumulating Snow Mid-Upper Elevations Into Thursday Morning ( Mainly At Upper Elevations During The Day ) And Across All Elevations Along The Upslope Side Of The Mountains ( WNW-NW winds ) During Thursday Night Into Friday Morning
This Will Be An Elevation Biased Snow Event Until Thursday Night, When All Elevations Will Have The Best Chance For Accumulating Snow & Widespread Hazardous Travel Conditions.
As of 11:00 PM Wednesday State Route 619, Routes 237 & 238, as well as others, at upper elevations in the High Knob Massif, were becoming icy and snow covered. Sticking snow levels will drop to around 1300-1700 feet by morning, then be mostly at elevations above 2500-3000 feet during the day before dropping to include the entire area along the upslope side of the mountains during Thursday Night into Friday morning ( * ).
*The GFS Model is colder on Thursday than the NAM Model. If the GFS verifies then sticking snow levels during the day will remain lower and generally be at or above 2000 feet ( lower amid any squalls ).
Due to strong upslope flow there will be a tendency for sticking snow at lower elevations along and southwest of the High Knob Massif and Tennessee Valley Divide ( 1300 feet ), than for lower elevations northeast-east of this high terrain ( 1700 feet ), into Thursday AM ( this morning ).
*Any snow squalls that may develop today could cause sticking and low visibility at any location, with subsequent melting & sunshine due to sinking air in their wake.
Overnight Into Thursday Morning
Any rain-sleet showers changing to snow showers. Blowing snow ( heaviest snow and best sticking along and southwest of the High Knob Massif-Tennessee Valley Divide at 1300-1500 feet or higher in elevation ). Windy. SW to W winds 15-30 mph, with higher gusts. Temperatures varying from 20-25 degrees at upper elevations to the lower-middle 30s. Wind chills dropping into the 10s and 20s, except 0 to 10 degrees along upper elevation mountain ridges.
Snow which sticks into Thursday morning may tend to melt at lower and middle elevations during the day, especially in places with southern exposures and during any hazy sunshine or breaks in the overcast ( even upper elevations will tend to have melting, especially across southern exposed slopes ).
The exception to the above will be northern slopes, especially at the higher elevations, and any place having a snow squall ( burst of heavy snow ) which could cause local sticking and significant reduction in visibility for short-periods of time.
A chance for snow showers & periods of snow at mid-upper elevations, with a mix possible at lower elevations ( below 2000 ft ). Local snow squalls ( bursts of heavy snow ). Some breaks in the overcast possible. Windy. Winds W-WNW 10-25 mph, with higher gusts. Temps from mid-upper 20s at upper elevations to the mid-upper 30s. Wind chills in the 10s & 20s ( locally colder in gusts at highest elevations ).
The most snowfall, and most widespread sticking with hazardous travel, is expected to develop Thursday evening into Friday AM.
Tonight Into Friday Morning
Snow showers & snow squalls. Snow may be heavy at times. Windy with blowing snow ( especially along exposed mid to upper elevation mountain ridges & plateaus ). NW winds at 10-20 mph, with higher gusts. Temperatures varying from the low-mid 10s at highest elevations to the mid-upper 20s ( milder at lower elevations toward the Tri-Cities ). Wind chills varying from single digits below & above zero at the upper elevations to the 10s to lower 20s.
Weather Discussion ( February 24-25 )
My Afternoon Update
Following some good overnight-morning snow a break with flurries and scattered, mostly light snow showers, has been the rule during the early-mid afternoon.
At 9:00 AM my friend Joe Carter, of the City of Norton Water Plant, measured 1.5″ of snowfall ( between 1-2″ on ground ). Since then there has been little additional sticking.
The City of Norton Water Plant reports 6.85″ of precipitation for the month of February ( 2.39″ with this storm event ), with 11.08″ since the beginning of 2016.
A general 2″ to 4″+ of snow depth is on the ground on Eagle Knob this afternoon, with around 3.0″ of snowfall being the estimate for the wind driven overnight & morning fall. The temperature on Eagle Knob has held steady or slightly fell amid lower 20s during the day ( wind chills have, of course, made it feel much colder in all locations today ).
My friend Darlene Fields measured 2.3″ on the ground at 5:10 PM in High Chaparral ( around 2.5″ or more of total snowfall with some settlement today ). This has, of course, been a difficult snow to measure given ROARING winds and by the end will require more figuring ( to figure it out )!
To the north, at Clintwood 1 W, I had just under 1.0″ of snow this morning which has now nearly all melted away with 35 degrees.
Flurries and light snow showers occurring now are due to a shift to more mid-continental air, with the 1:00 PM analysis from the NAM 12 KM Model showing this well.
*The NAM Model ended up beating the GFS Model on afternoon coverage, but temperatures on the GFS Model have been closer to reality than those predicted by the NAM. Yet again this illustrates that no model is correct, with forecasters needing to follow actual conditions, use past climatology of similar conditions, and try to use the model, or blend of models, that fits the setting best.
ALWAYS keeping in mind the known model biases which research by Baker & Konrad clearly show places too much emphasis on locations near the ECD ( Eastern Continental Divide ) relative to the western front range of the mountain chain ( likely the largest model errors in all of the southern Appalachians, according to my data, is centered upon the High Knob Massif where much more snow falls than is forecast by computer models on NW Flow & other flows ).
Graphic Above Courtesy of: Relationships between NW flow snowfall and topography in the Southern Appalachians, USA by authors L. Baker Perry and Charles E. Konrad.
Forecast models consistently under-estimate snowfall along the western front of the southern Appalachians, with largest model errors showing up on Mount LeConte, Wise, and Beckley.
Forecast models consistently over-estimate snowfall along the ECD from Virginia down along the TN-NC border ( except for the highest peaks ) during NW Flow events.
If observed snowfall in the High Knob Massif ( e.g., High Chaparral and the main crest zone ) was factored into this it would easily be the largest under-estimation in the southern Appalachians.
Yet most forecasters, unaware of this research and my 27 years of collecting snowfall, including the Weather Channel, consistently neglect this research and place heaviest snow amounts along the ECD indiscriminately ( including places like the New River Valley and many sites along the NC side of the border where snowfall tends to be much less during many such events ).
*I grew up watching The Weather Channel always place a strip of heavier snow down along the ECD to the east of Norton-Wise and Clintwood. I said, “that just doesn’t look right to me.” I started measuring snow when I was just 10 years old and began to see it was not right. Wise, officially the snowiest Town in Virginia, was always being left out ( in the cold )!
Due to abundant mid-level moisture there have been no breaks in the overcast to make the lower-levels more unstable, limiting heavier snow showers and squalls.
An upper wave approaching will help turn the low-level flow back off the Great Lakes tonight into Friday morning.
This will increase snowfall again as the coldest temps this system offers move into the mountains on NW upslope. I expect hazardous travel conditions to become widespread along the upslope side of the mountains into Friday AM.
A general 1″ to 3″ of new snow, with locally more possible atop the High Knob Massif, will put event snowfall totals into ranges that I originally forecast a couple days ago.
My Overnight Discussion
Reference my 022416 Forecast & discussion for more details on this past day of turbulent weather conditions.
Yet another phase of a powerful late season winter storm has now been entered, with complexity remaining in the forecast for today into Friday. I have tried to condense it above, with emphasis on this being an elevation biased snowfall event through today ( i.e., better sticking-snow with increasing elevation through today ).
Observe temperature changes which occurred today…between 7:00 AM and 7:00 PM…as this monster-sized storm swirled across the region, triggering a Tornado Outbreak in eastern Virginia.
A deadly and destructive tornado outbreak in eastern Virginia.
Observe the 850 MB wind field changes between 7 AM and 7 PM.
Colder air has been driven into the area on SW winds.
At Midnight, for example, roads & the ground are covered atop the High Knob Massif while nothing has stuck at my official NWS station in Clintwood ( with wind driven sleet being the main precipitation type during the evening ).
*The Midnight temperature was 24 degrees atop the High Knob Massif with wind chills in the single digits. By contrast, the air temperature was 36 degrees in Clintwood.
There is a natural tendency, due to strong upslope flow, for sticking to occur at lower elevations along & southwest of the High Knob Massif & Tennessee Valley Divide on SW-WSW flow through the overnight into Thursday morning than for locales northeast-east of this high terrain. This is exemplified at the present time by differences between Jonesville & Birchleaf:
Jonesville & Birchleaf are both close to the same elevation above sea level, but strong SW upslope flow is making the air cooler in Jonesville ( 32 degrees ) than Birchleaf where SW air flow sinks and warms into the Russell Fork basin. The midnight temp in Clintwood was also 36 degrees.
Today the atmosphere becomes more unstable as temp drops with height increase. Although the NAM Model is actually not forecasting any snow to fall this afternoon, that seems unlikely given enough moisture to generate snow showers and some hit or miss snow squalls ( as the atmosphere gets more unstable the chance for developing bursts of heavy snow will increase in a hit-miss fashion ).
Air tends to converge into snow squalls and snowstreaks and to subsequently sink ( as demanded by atmospheric compensation ) around their peripheries. Sinking air opens up clouds to sun that then acts to make the lower atmosphere more unstable, forming a feedback cycle that then feeds upon itself to help develop more snow squalls and/or streaks.
*Since the 850-700 MB flow will become unidirectional this also increases the chance for snowstreaks ( a train of squalls ) to form today as flow comes south off the Great Lakes. Any places having a snow squall, or snowstreak, could accumulate snow during the day while in general the best sticking today will be at highest elevations and northern exposed locations.
By this evening into Friday morning conditions begin changing as the coldest air this system has to offer is transported into the mountains ( 850 MB thermal MIN ), along with a period of deep moisture & upper divergence which is joined and followed by good NW Upslope Flow. Therefore, the most snow and best accumulations will become most likely tonight into Friday morning.
*Some places may have little to no snow accumulation until this period ( Thursday Night into Friday Morning ).
Nice diffluence aloft at 500 MB and PVA will be beneath good speed divergence at 300 MB.
Combined with excellent NW upslope flow and moisture from Lake Michigan the stage will be set for accumulating snow showers, squalls, and maybe some streaks.
The Thursday evening through Friday morning period should produce the best ( most ) snowfall of this event, along with the most widespread hazardous travel.
*There is an excellent chance for many more school schedule changes Friday than into this morning ( Thursday ).
ALERT For A Major Winter Storm Impacting The Mountain Region Wednesday-Friday Morning With Strong Winds, Rain, Possible Thunderstorms, And Significant Snow-Rime At Mid-Upper Elevations
The General Order For This Event
Rain showers & rain increase during the overnight. Downpours will become possible, especially along upslope favored locales on SE to SSE winds.
Wind speeds increase at mid-upper elevations with potential for mountain wave development and impacts in valleys leeward of the High Knob Massif, Clinch Mountain, Pine & Black mountains in the overnight-morning hours of Wednesday.
A broken or solid line of downpours, with possible thunderstorms, is roughly timed to arrive from southwest to northeast during the sunrise to mid-day period ( around 8-9 AM for Norton-Wise ).
Any break then gives way to redevelopment of showers, with possible downpours ( thunder can not be ruled out ) along and just ahead of the surface cold front during Wednesday afternoon.
A sharp temperature drop occurs as winds become very strong and gusty ( ROARING ) across the area between 4:00 PM and 7:00 PM as the cold front passes. I can not STRESS ENOUGH that WINDS Will ROAR along and behind this cold front.
Rain showers change to wind driven snow by late afternoon into the evening for locations along the Virginia-Kentucky border, with sticking starting first at highest elevations and working downward into middle-lower elevations over time.
Significant snow ( with riming in upper elevations ) is expected Thursday-Thursday Night into the predawn hours of Friday for middle-upper elevations.
Threat for severe thunderstorms remains relatively low, but shear will be so strong that a severe thunderstorm can not be ruled out ( with increasing threat for severe storms across central-eastern Virginia into the Carolinas today ).
Due to such strong gradient winds and shear the main threat today, whether with thunder or not, remains wind damage for all locations in the mountain area. This raises the potential for power outages and local tree damage.
Rain showers. Becoming very windy along middle-upper elevation mountain ridges ( and in mountain wave zones ). Downpours possible, with a chance of lightning-thunder into morning. SE-SSE winds increasing to 10-25 mph, with higher gusts, on mountain ridges-plateaus below 2700 feet. SSE winds 20-35 mph, with gusts 40-50+ mph, on upper elevation mountain ridges. Unseasonably mild with temperatures in the 40s to middle 50s.
Mountain waves will become possible into Wednesday morning, with strong to locally severe wind gusts in favored breaking zones from Powell Valley in Wise County to the Clinch Valley of Russell-Tazewell counties ( and immediately next to the Kentucky side of Pine Mountain and Black Mountain ). Some questions remain as to how an atypically low inversion level will impact these waves.
Due to 1.00″ to 1.50″ of rain during the past couple of days, any prolonged moderate rain or downpours will need to be respected through today until colder air arrives ( ponding of water in low lying and poor drainage areas, rises on streams, will need to be followed closely until after the cold front passes ).
A dramatic weather change will occur this afternoon along and behind a strong cold front, with ROARING winds as a very strong pressure gradient begins driving and funneling SW flow upslope through the High Knob Landform into the Norton-Wise area and adjacent locations. This will be the windiest period for the entire area as a whole, with strong winds extending into the evening.
Mid-Morning Through This Afternoon
Showers redevelop following any brief break. A chance for downpours. Thunder possible. ROARING WINDS develop in all locations along and behind a strong cold front. Showers of rain change to snow late. Winds shifting SSW-SW at 20-40 mph, with higher gusts. Temps plunge from the 50s to around 60 degrees into the 30s to around 40 degrees by sunset to early evening. Wind chills dip into the 20s.
Blowing snow and drifting will develop overnight into Thursday amid upper elevations in the High Knob Massif, along with rime formation at elevations above 3000 to 3500 feet.
Tonight Into Thursday Morning
Any rain showers changing to snow showers during the evening. Snow overnight, heavy at times ( especially along and southwest of the High Knob Massif & Tennessee Valley Divide ). Windy. SW to W winds 15-30 mph, with higher gusts, at elevations below 2700 feet. SW-W winds 20-35 mph, with higher gusts, along upper elevation mountain ridges. Temps varying from lower 20s to lower 30s by morning ( coldest at highest elevations ). Wind chills dropping into 10s & 20s, except single digits at high elevations in the High Knob Massif.
Snowfall Forecast For The February 24-26 Period
Target Snowfall of 4″ in Norton-Wise ( +/- ) 1.5″ Spread Potential. This implies snowfall totals from 2.5″ to 5.5″ will be possible with variations expected on the ground due to an unfrozen, wet state day-time settlement-melting, and blowing by strong winds.
A general 4″ to 8″ of snow is expected above 3000 feet amid the High Knob high country, with locally higher totals possible. Large ground depth variations are expected due to blowing and drifting at the highest elevations ( with significant rime formation ).
*In general this is expected to be an elevation biased event, with increasing snow depth with increasing elevation. Snow squalls and/or snowstreaks that may develop Thursday could locally skew this general trend.
Weather Discussion ( February 23-24 )
Late Afternoon Update
It has been quite a weather day across the mountain area, with ROARING winds and ROARING water. As of 6:00 PM it has gotten cold enough for the first flakes of snow to begin falling atop the High Knob Massif ( at summit levels ).
However, most of the snow will begin to come in later during the evening and into the overnight period and Thursday morning.
Meanwhile, it is very dangerous around trees as gusts are making them pop and crack. I was just outside to hear it first hand, so please use caution in these high winds.
The only update to my forecast late this afternoon being to ease wind speeds up even more, than I had them before, for tonight.
Sustained winds between 20 and 30 mph have been common at middle to upper elevations this afternoon, with gusts topping the 50 mph barrier atop the High Knob Massif and Black Mountain.
Outside of any mountain wave gusts and roaring winds along high mountain crest lines, the real ROAR began in most places along and behind a mid-morning squall line with heavy rain that passed through the Norton-Wise & Clintwood-Pound area during the 9:15-10:15 AM period.
Winds have truly been a ROAR with many twigs, limbs, and other debris scattered across the area, including some trees. Power outages have so far been localized ( thankfully ).
More than 1.00″ of rain since Midnight, upon already wet ground, has pushed steep creeks draining the High Knob Massif into a pounding ROAR.
As of 3:15 PM the Big Stony Creek stream gage showed the level was just 14″ below flood stage. Similar conditions are occurring on South Fork of the Powell River and adjacent steep creeks from Clear Creek to Little Stony Creek.
With colder air now pouring into the mountain area, and showers of rain that will change to snow tonight at mid-upper elevations, these high stream levels should gradually drop ( but please use caution around these creeks and their slick-rocky banks ).
My Overnight Discussion
A beautiful array of mountain wave clouds developed along the High Knob Massif during Tuesday afternoon, even if the high winds aloft had not yet reached the surface in valleys.
I have labeled a few views to illustrate the different types of orographic clouds being generated.
It was magical to watch how the massif interacted with air flow to generate these magnificent clouds ( these views not doing them justice, as would seeing them via your eyes ).
While some clouds changed continuously with air flow rushing over the massif, other clouds held their forms and were long-lived in nature ( e.g., the orographic cap cloud mass and standing wave cloud which varied little in position over time ).
Observe the long-tail which developed around sunset on the wave cloud capping the massif ( below ).
This cloud later developed a fish-tail form, and it was a shame to see darkness fall with such beautiful wave clouds taking on these majestic shapes.
The CAM switched into IR Model for better night vision.
Focus now shifts to a powerhouse winter storm system that will impact weather into Friday. Models have not changed much locally from what I highlighted in my discussion last night, with an increasing risk for severe thunderstorms and possible tornadoes from central-eastern Virginia south into central-eastern portions of the Carolina’s.
However, this area will have to closely watch a squall line of downpours ( with possible thunderstorms ) that is currently timed to move across far southwestern Virginia during the 7:00 AM to 10:00 AM period.
The 1:00 AM run of the High-Resolution Rapid Refresh ( HRRR ) Model has the squall line over Norton-Wise at 9:00 AM. Timing could, of course, be off some but this is the current trend.
Downpours of heavy rain and strong to potentially severe gusts of wind will have to be watched for during this time given such strong winds roaring across the high mountain summits ( and aloft ).
There remains a period today when models want to allow some surface based convective available potential energy, called SBCAPE, to develop amid still strong shear.
It is the lack of instability through this morning that will greatly limit the severe potential ( and a inversion layer aloft ) relative to what it would be with this ( below ) if significant instability was present to form surface based convection ( which in this type of high shear environment would easily be capable of developing rotating updrafts ).
Shear and the magnitude of helicity relative to how a storm updraft could be driven to rotate becomes simply extreme by the predawn-morning hours of today, but instability is lacking ( thankfully ). Still this does not rule out a severe thunderstorm developing into this morning and will tend to increase the risk of strong-severe winds along a squall line which may move across the area this morning.
Models say that the southern portion of the Tennessee Valley will have the greatest severe thunderstorm potential heading into this morning, with the best overlap of shear and instability.
As time passes, we will have to see if this potential may work northeastward up the Great Valley and into the Mountain Empire in advance of the surface cold front to provide one more period where severe thunderstorms ( outside any morning squall line ) and/or severe downdrafts in showers will be possible.
Clearly the best overlap of shear and instability will be developing east of the mountains by later this afternoon-evening into central portions of Virginia & the Carolina’s.
A severe outbreak could develop there as snow begins to fall atop the High Knob Massif, which, by no coincidence, has happened during past events as well documented by climatology.
One change from yesterday is that models are a little faster in bringing in the cold air, with the 0 degree ( 32 F ) freezing line overspreading far southwestern Virginia between 4 PM and 7 PM, on simply ROARING SW winds along and behind a strong cold front. It would not be impossible to go from rain & thunder to snow in just a short time.
From this point onward it will be all about the wintry side of this storm system, with strong orographic forcing continuing into the Thursday Night-Friday AM period. The flow being better for the City of Norton to get more snow than Wise, but time will tell about that ( as regards Norton vs. Wise snowfall totals ).
Stay tuned to NOAA weather radio for any possible warnings that may be needed through today.
ALERT For A Major Winter Storm Impacting The Mountain Region Wednesday-Friday Morning With Strong Winds, Rain, Possible Thunderstorms, And Significant Snow-Rime At Mid-Upper Elevations
Overnight Into Tuesday Morning
Rain developing. Becoming steady and soaking into the overnight, especially along and southeast of the VA-KY border. Winds becoming ESE to SSE at 5-15 mph, with higher gusts, on mid-upper elevation mountain ridges. Temps widespread in the 40s ( dense fog developing in upper elevations – patchy fog in other locations ). Wind chills in the 30s along upper elevation mountain ridges.
This Morning Through This Afternoon
Mostly cloudy. A continued chance for rain showers. Winds SE-SSE at 5-15 mph, with higher gusts, below 2700 feet. SE to S winds 10-20 mph, with higher gusts, on upper elevation mountain ridges. Temperatures widespread in the 40s to lower 50s. Areas of dense fog possible, especially along high mountain ridges.
Mountain waves will become possible Tuesday Night into Wednesday morning, with strong to locally severe wind gusts in favored breaking zones from Powell Valley in Wise County to the Clinch Valley of Russell-Tazewell counties ( and immediately next to the Kentucky side of Pine Mountain and Black Mountain ).
Tonight Into Wednesday Morning
Rain showers. Becoming very windy along middle-upper elevation mountain ridges ( and in mountain wave zones ). Downpours possible, with a chance of lightning-thunder overnight into morning. SE-SSE winds increasing to 10-25 mph, with higher gusts, on mountain ridges-plateaus below 2700 feet. SSE winds 20-35 mph, with gusts 40-50+ mph, on upper elevation mountain ridges. Unseasonably mild with temperatures in the 40s to middle 50s.
A squall line of rain, with embedded thunderstorms, will be possible early Wednesday well in advance of an approaching cold front. Instability during the afternoon may aid formation of low-topped convection, with northeast movement through the Great Valley toward the Cumberland Mountains along this cold frontal boundary. The greatest threat will be potential for wind damage.
Given recent wetness, and Winter 2015-16 wetness in general, any moderate to heavy rainfall will be capable of causing strong rises along creeks as well as ponding of water in poor drainage and low lying locations during Wednesday.
A sharp temperature drop will follow with rain changing to snow during Wednesday evening in upper elevations of the High Knob Massif. Snow levels will drop in elevation into Thursday AM.
Significant snow accumulations will be possible at mid-upper elevations during the Wednesday Night-Friday Morning period, with preliminary snow totals of 3″ to 5″ in the Norton-Wise area, 4″ to 8″ in the High Knob Massif ( above 2700 feet ), and 1″ to 3″ amid lower elevations around Pound, Clintwood & Clinchco.
Stay tuned for later updates.
Weather Discussion ( February 22-23 )
Monday ended up being the best day of this work week to come, with lifting of cloud bases and gloomy but rain free skies as temperatures ranged in the 40s to middle 50s.
Rainfall totals of 0.70″ at the City of Norton Water Plant and 0.64″ in Clintwood were measured Sunday into early Monday morning.
A lead wave is spreading a steady, light to moderate rain across the mountain area tonight well in advance of the main system developing over Texas ( the big storm ).
Models had initially predicted rain tonight to remain mostly southeast of the area; however, a progressive northward shift will now allow for the most widespread, steady rain to fall along and southeast of Pine Mountain of the Cumberland Overthrust Block.
This rain will further saturate an already soggy ground to make water level rises with the main system on Wednesday potentially more problematic than if today had remained dry.
Focus now shifts to the main storm event.
Exceptional storm relative helicity, driven by strong wind shear, will be in place early Wednesday as showers & storms develop. This will need to be closely watched despite a lack of any SBCAPE ( surface-based convective energy ).
SBCAPE = Surface Based Convective Available Potential Energy
An idea of the wind shear driving the strong SRH values can be obtained by looking at the cross-over flow in the vertical ( surface-850 MB-500 MB vectors overlaid ).
Both speed + directional shear in the vertical is acting to drive these extreme storm relative helicity values ( above ). Superimposed upon this setting will be a mountain wave formation potential in breaking zones.
One of the interesting aspects of this storm event is that height falls will be so significant that the 850 MB level will actually drop down below the summit level of the High Knob Massif for a time. The inversion level above is very low and it will be interesting to see how this may impact mountain wave formation.
Heights refer to the level of a particular isobaric surface, such as the 850 MB level. It is typically around or just below 5,000 feet. In this case, it will be dropping down to around the 4,200 foot level of the High Knob Massif. That tends to indicate a very strong storm system developing, with falling heights indicative of large changes in mass within a vertical column of air.
Since warm air advection will be occurring against these height falls it means that the warm advection is being mostly applied to upward vertical motion, or large-scale lift. Otherwise, the WAA would act to pump up heights and raise them to higher levels.
During Wednesday afternoon the SRH values begin to decrease amid the warm sector ( remaining very high within the most stable wedge zone with CAD to the east ).
SRH = Storm Relative Helicity
CAD = Cold Air Damming
There remains a notable gradient in the High Knob Massif, northeast Tennessee Valley zone, that needs to be watched.
The difference is models are showing some 500-1000 J/Kg of surface-based CAPE, which could generate low-topped convection with a wind damage potential ( as climatology during past such settings would suggest ). This will need to be closely followed through the day on Wednesday.
CAPE = Convective Available Potential Energy
During this time period an inverted-V type of low-level sounding is suggestive of a marginal tornado risk, or brief spin-up, should this SBCAPE actually develop ( this will be more likely should breaks develop in the overcast to allow surface heating in between rain showers ). Otherwise, beneath solid overcast this risk would remain minimal.
The current Storm Prediction Risk regions up to 7 AM Wednesday ( February 24, 2016 )
The main risk region for severe thunderstorms is forecast to shift east of the Appalachians through Wednesday into early Thursday.
The cold side of this storm begins Wednesday evening as rain changes to snow from top to bottom over time, with early evening featuring a change at the High Knob Massif summit level as cold air surges quickly in from the SW.
Moisture remains deep from the surface up through 700 MB to signal that significant snow will be likely, with a notable Lake Michigan connection currently being forecast.
I show the 700 MB RH and Flow Charts since 925-850 MB moisture remains copious = great moisture for snowfall production as was observed during much of the January 2016 storm event ( although snowfall amounts this time will be much less but still productive ).
In this case the 700 MB moisture field being especially important since it will maintain dendritic crystal growth as moisture reaches into -12C air or colder ( in this case that would not occur if the 700 MB moisture was not present since the summit level pilatus cloud temperatures reach only around -10 C at the end of this event ).
Due to the thermal structure the best snow accumulations will occur across middle-upper elevations above 2000 feet, with heaviest snow likely above 3000 feet in the High Knob Massif where excellent orographic forcing and exposure will exist during this event.
Orographic Forcing = not only wind speed + direction but many other factors such as moisture and riming of snowflakes which increases snowfall volume, massif width which enhances snow amounts as well & tends to reduce carry-over to lee side valleys
This will again be a setting where more snow is likely to fall and accumulate on above ground objects than the ground, with depths being less than the total snowfall outside of drifting amid upper elevations, where wind blown snow and riming will be factors.
Lower elevations, below 2000 feet, and especially those downslope of the mountains will have a harder time accumulating snow in daylight hours ( best opportunities being after darkness falls ).
The Alert for Dense Fog has been cancelled due to drier air working into the lower-level northerly flow today. Lowering clouds again are likely into this evening with a chance for some showers.
Overnight Into Mid-Morning Monday
Rain & showers tapering to drizzle. W-WSW winds 5 to 15 mph, with higher gusts, shifting NNW to NNE. Cloud bases dropping to obscure middle elevations in dense fog. Temps dropping into the upper 30s to middle-upper 40s by morning ( coldest at the highest elevations ).
Mid-Morning Through This Afternoon
Mostly cloudy ( cloud bases may lift off middle elevations ), with a few breaks possible. Light N-ENE winds at generally less than 10 mph. Temperatures varying from low-mid 40s to the low-mid 50s ( coolest at highest elevations ).
*High-resolution Models continue to ease the rain shield farther north and northwest tonight, such that I have updated again for the widespread development of rain ( steady, soaking rainfall ).
Tonight Into Tuesday Morning ( Updated 8:00 PM )
Rain developing. Becoming steady and soaking into the overnight, especially along and southeast of the VA-KY border. Winds becoming ESE to SSE at 5-15 mph, with higher gusts, on mid-upper elevation mountain ridges. Temps widespread in the 40s ( dense fog developing in upper elevations – patchy fog other locations ), with some upper 30s to near 40 degrees atop the High Knob Massif.
A Major Winter Storm system will impact the mountain region during the February 24-26 period with strong winds, rain and a potential for significant snowfall. Preliminary indications for heaviest snowfall amounts are at middle-upper elevations from Wednesday Night through Friday ( starting at highest elevations with snow levels dropping over time ) on SW to W-NW winds.
Low pressure will intensify & become very strong as it moves from Texas toward New York State and the eastern Great Lakes between Tuesday AM and Thursday AM. Multiple facets with this powerful winter storm system include strong winds ( with mountain wave formation possible on SE-SSE flow ), heavy rain, and a transition to snow in the backside circulation. No snowfall amounts have been forecast yet, and the “Major” aspect is due to this being the winter season with a potent low pressure formation, so yes, any way this is dissected, it will be a Major Winter Storm System. Details are yet to be worked out, including specific snow amounts. Stay tuned.
Weather Discussion ( February 21-22 )
A look at low-level moisture this morning reveals that drier air has worked into the area northwest of last night’s front, and my update is to cancel the dense fog advisory.
Dissipation of low clouds has locally occurred to actually reveal summit levels of the High Knob Massif at 10:28 AM ( above ).
A look at the NAM Model sounding above Wise at 7 AM found most of the vertical column to be unsaturated, except right at the surface which has now been able to mix out. An array of mid-high clouds remain aloft.
While cloud bases will drop again by this evening, with luck this will offer some breaks for hazy sunshine and somewhat milder PM temperatures that may break above 50 degrees at lower-middle elevations ( I have opened the range a little ).
The latest stream level shows that steep creeks continue to gush with whitewater this morning in wake of recent snow melt and rainfall, with Big Stony Creek being near the 4.0 foot RED Alert Stage. While levels should begin to drop by later today, caution is advised around slippery-rocky banks of these roaring creeks.
My Overnight Discussion
A damp and gloomy Sunday graced the mountains with rumbles of thunder, to boot, well in advance of a frontal boundary that is just now pushing across the Virginia stateline at 12:10 AM ( February 22 ).
An old mountain saying states…if it thunders in February it will frost on the same day in May! So mark that down now, and time will tell how close it is to reality this year.
Upper elevations in the High Knob Massif have been amid the clouds for the better part of 30 hours now, with many more hours to go before this dense fog will clear for any prolonged period of time. High-resolution models are somewhat less aggressive in holding moisture in today, with only shallow moisture available that might have, given some luck, a chance to break up for a while.
A problem, of course, in telling exactly how today will play out arises since this frontal boundary stalls out over the mountain region today. One reason model runs tonight are a little milder than last night with the boundary barely clearing the High Knob Massif area into this afternoon ( being just east-southeast ).
The big show, of course, that will dominate this week will be an intense low pressure that rapidly deepens ( gets strong ) as it lifts out of Texas into the Ohio Valley.
This will be one of the strongest storm systems of the entire winter season, and presents classic formation.
Doing some old school hand analysis, the phasing region for intense cyclogenesis really shows up well at 300 MB by 7 AM on Wednesday, with coupling between the Left Front Exit region of a Sub-tropical Jetstreak & the Right Rear Entrance sector of a Polar Jetstreak. Large-scale divergence aloft will be evacuating mass, which by atmospheric compensation is replaced by inflow of air at low-levels where convergence and spin-up occurs amid intensifying low pressure.
The Interaction of Jet Streak Circulations during Heavy Snow Events
along the East Coast of the United States
LOUIS W. UCCELLINI AND PAUL J. KOCIN
For those wanting to learn more about how this works, the classic winter storm generation paper by Louis Uccellini and Paul Kocin from back in 1987 is a good point to start.
Uccellini, L.W., and D.R. Johnson, 1979: The Coupling of Upper and Lower Tropospheric Jet Streaks and Implications for the Development of Severe Convective Storms. Mon. Wea. Rev. 107, 682-703.
The isallobaric component of this ageostrophic wind equation, above, which I mathematically derived from scratch some time ago is an important part of driving this:
This monster winter storm system is going to become a wind machine, which means orographic forcing is going to crank ( remembering with forcing there is both positive and negative forcing generated ). The setting above, being for a strongly positive Mountain Torque force as the mountains push back against the atmospheric wind field.
Cold air surges in from the southwest with rain changing to snow at higher elevations Wednesday Night. Given plenty of low-level moisture and strong forcing there is no doubt significant snow will fall across upper elevations in the High Knob Massif with winds also later shifting W-NW.
If this low had tracked farther south and eastward, instead of west and northwest, it would have been like the February 1985 Blizzard which required my friend Carl Henderson of Wise to be air lifted off Eagle Knob of High Knob after the storm ended.
*The late Carl Henderson was an electrical engineer at the Blue Ridge Public Transmitter Station on the summit. Carl was a wonderful person and luckily had snowshoes, which he wore to reach a clearing where an Apache-Jet Helicopter landed to pick him up. The extraction was needed since Carl was a diabetic and running out of medication ( plus he was also getting cold with minimal heat in the building ). I’ve written about his adventure, which also was documented by newspapers. I can not say enough good things about this man and his wife. He made a positive difference in the world, and surely that is the best we can hope for.
Meanwhile, this will be no February 1985 blizzard but it will be a very intense & interesting ( dare I say ) storm to follow through coming days.
Have a great Monday.
My dense fog ALERT for Middle Elevations appears to have been right on target. Please slow down and take it easy my friends!
ALERT For Areas of Dense Fog & Low Cloud Bases Along And Southwest Of The High Knob Massif & Tennessee Valley Divide Overnight Into Sunday On SW Flow
*As of 12:30 AM on February 21 dense fog was widespread at elevations above 2800-2900 feet ( but will be locally lower in favored upslope locations on gusty SW winds ).
Dense fog ( orographic clouds ) has formed on SW Upslope Flow tonight and will be most favored for locations along & southwest of the High Knob Massif and Tennessee Valley Divide into Sunday as rainfall develops ( e.g., from the Wise area southwest along the U.S. 23 corridor toward Big Stone Gap where funneling of SW air flow tends to lower bases into Little Stone Mountain Gap and the Powell Valley Overlook section. Caution is Advised for travelers ).
Thunderstorms Will Be Possible Today, Embedded In The Rain Shield. Caution Is Advised For Lightning.
Strong Rises Will Be Possible On Steep Creeks That Drain The High Knob Massif, Where Snow Melt Has Stream Levels Above Average At The Current Time.
ALERT For Dense Fog Formation From Late Sunday Night Into Monday At Middle-Upper Elevations Along And North Of The High Knob Massif-Tennessee Valley Divide On NNW-NE Upslope Flow
While any location could have fog after rain develops Sunday, the above ALERT is for widespread drops in cloud bases with northerly upslope flow behind a cold front late Sunday Night into Monday.
Very dense fog is expected to develop along and northward of the High Knob Massif and Tennessee Valley Divide toward Midnight into the overnight-sunrise period of Monday.
Overnight Into Sunday Morning
Low clouds. Areas of dense fog & drizzle. A chance of light rain developing. SW winds 5-15 mph, with higher gusts, on mountain ridges-plateaus below 2700 feet. SW winds 10-20 mph, with higher gusts, along upper elevation mountain ridges. Temperatures varying from the middle 40s to the lower 50s ( coolest at higher elevations and in sheltered valleys with light winds ). Wind chills in the 40s, except some 30s at highest elevations in gusts.
This Morning Through This Afternoon
Rain. A chance for thunder. Locally heavy rain possible. Rain becoming showery in nature late. SW-WSW winds at 10-20 mph, with higher gusts, along mid-upper elevation mountain ridges & plateaus. Areas of fog. Temperatures varying from the upper 40s to upper 50s.
Tonight Into Monday Morning
Rain & showers tapering to drizzle. W-WSW winds 5-15 mph, with higher gusts, shifting NNW-NNE. Cloud bases dropping to obscure middle elevations in dense fog ( chance for freezing fog-drizzle at highest elevations amid the High Knob Massif by morning ). Temperatures dropping into the lower 30s to lower-middle 40s by morning ( coldest at the highest elevations ).
A Major Winter Storm system will impact the mountain region during the February 24-26 period with strong winds, rain and a potential for significant NW Upslope Flow snowfall. Stay tuned for updates on this developing storm system.
An interesting setting was on display Saturday afternoon as widespread cloudiness along-south of the High Knob Massif was in contrast to partly sunny skies to the north.
Upslope flow across the still snow covered High Knob Massif allowed cloud bases to obscure upper elevations and form a very nice and persistent capping cloud mass.
Conditions inside the capping cloud mass featured dense fog and air temperatures in the mid-upper 40s. Snow cover remained solid and deeper across northern slopes, with a little bare ground being visible along wind swept crest lines ( as on Eagle Knob below ).
Continuing melt of the previously 10″ to 20″ snowpack is keeping stream levels elevated, above average, on steep creeks draining the High Knob Massif tonight.
While forecast models predict the heaviest rain today to remain north of the area, along the surface low pressure track, any downpours ( especially if convective in nature ) could quickly raise these already elevated stream levels.
There will be potential for orographic enhancement on SW-WSW flow into the High Knob Massif area, as suggested by the NAM 4 KM Model along the Appalachians ( it tends to under-estimate enhancement in the High Knob Massif ).
The Bottom line – While no flood watches are officially in effect it will be wise for everyone living and driving along these already elevated steep creeks to monitor water levels today ( especially if rainfall becomes heavy with thunder ).
The focus by later tonight into Monday will be on a drop in cloud bases with upsloping northerly air flow that will be forced to rise upward from the Kentucky foothills into the High Knob Massif and Tennessee Valley Divide.
Depending upon how long the NW-NE air flow persists, low cloud bases & dense fog could be a factor for Wise and many other sites across Wise, Dickenson, and extreme northern Scott counties well into Monday ( worst case scenario being all day into the evening ).
A harsh winter pattern during the February 8-15 period has currently relaxed. This has been a repetitive pattern since mid-January and is illustrated well by build-up and melting of snowpacks amid the High Knob Massif.
Whitewater tends to gush when levels reach 2-3 feet, with increasing volume toward RED Alert level resulting in pounding whitewater that ROARS loudly as it plunges along the many steep creeks draining the border area of Wise, Scott, Lee counties.
A long period of enhanced run-off began during the period of January 24 to 26 and continued through the first week of February as snow melt combined with early February rain. Snow depths peaked at 1-2+ feet on January 23-25.
Melt of the current snowpack is ongoing with solid snow still across northern slopes, at upper elevations, late on February 20. Depths peaked between 10″ and 20″ during February 15 at elevations above 3000 feet in the massif.
A mean snow depth of 8″ was measured at the City of Norton Water Plant on February 15, at the northern base of the massif.
Reference Winter Majesty In The High Knob Massif to see actual precipitation totals recorded during this period from Big Cherry Lake Dam & heads of basins for High Knob Lake, Big Cherry, and the Dual Norton Reservoir system.
As noted in my last extended outlook, winter temperatures this season have been correlated to the Arctic Oscillation to a high degree, with negative phases associated with colder than average conditions and positive phases with milder than average temperatures.
Observe that much of January 2016 had a -AO and mean temps were colder than average in the mountain area. The harsh period of February 8-15 is also correlated to a dip back to -AO, with the snowpack melt downs in late January-early February and at the present time associated with +AO phases ( positive phases ).
Naturally, therefore, the future trend of the AO will be of great interest and will likely be associated with how the pattern in the eastern USA trends.
Both the GFS & GEM ( Canadian ) model ensembles predict that a negative trend in the AO will begin on February 21 and continue through the first week of March ( European Ensembles agree well with these forecasts ).
Note I use ensembles and look for the MEAN since they tend to be more accurate than any given model run. The indication is solid for a prolonged negative phase of the Arctic Oscillation to occur.
Another strong indicator of a cold pattern redeveloping is the continuation and increase in strength of a +PNA phase which tends to be highly correlated to western USA ridge and eastern USA trough formation.
Note that means of both model ensembles remain positive through the first week of March ( the European Ensembles again agree with this +PNA forecast ).
This western USA ridge and eastern USA trough pattern is very well developed on the European Ensembles by later this week ( Friday, February 26 above ). A cold signal.
In addition, a NW Upslope Flow setting in wake of a strong middle latitude cyclone is likely to result in significant snowfall along the upslope side of the southern-central Appalachians with largely open expanses of water across Lake Michigan & Lake Superior.
The 51-Member European Ensembles are, in fact, showing a very cold signal for late this week into the early weekend.
Note these temperatures are in degrees Celsius, such that the departure in degrees Fahrenheit is around 20 degrees below average for this time of year by Friday-Saturday ( Feb 26-27 ).
There is increased confidence in these forecasts since they are once again correlated to major stratospheric changes via a polar vortex split, with one lobe moving to between eastern Greenland & western European as the other lobe relocates toward western Siberia. This promotes ridging amid the upper air to reinforce the +PNA pattern.
The splitting of the Polar Vortex and ridge formation in between the two lobes is illustrated above by the DAY 10 forecast from the European Model ( note that stratospheric forecasts out to DAY 10 tend to be more stable and are often better predicted than a DAY 10 forecast in the troposphere ).
Impacts of this are seen in the Mean Zonal Temperatures with a forecast rise from -85+ degrees Celsius above the North Pole on February 19 to around -55 degrees Celsius above the North Pole by February 29 ( below ), with more warming predicted beyond this point.
This forecast is for a 50+ degree Fahrenheit rise in temperature.
Another graphic illustrating the impacts of this are the zonal mean zonal wind changes through the atmosphere.
Observe the lack of easterly flow above the North Pole and the mean Polar Frontal Zone JET Position ( above ) analyzed at 7 AM on February 19 ( around 38 degrees N latitude ).
While this may or may not again meet currently accepted technical criteria for a Major Sudden Stratospheric Warming Event ( i.e., reversal of winds at 60 N and 10 MB ), the impacts combine with the previous episode to continue Polar Vortex disturbance and suggests via past climatology that prolonged negative trends in the Arctic Oscillation can be expected for a period of approximately 4-6 weeks. This alone suggests that March will tend to be colder than average in the eastern USA.
In 10 days winds above the North Pole reverse to easterly in direction and the mean Polar Front JET Position has dipped southward to around 30 degrees North Latitude.
Although not a huge force this winter, it should be noted that the Madden-Julian Oscillation is also forecast to move into Phase 8 through the first week of March, which is a cold signal for the eastern USA.
The Madden-Julian Oscillation ( MJO ) is a synoptic-scale linkage between the atmosphere and tropical deep convection that unlike the standing wave pattern represented by ENSO takes the form of a traveling wave which propagates through equatorial regions on a 30-90 day period, forming intraseasonal variability with impacts beyond the immediate forcing region of the tropics.
Yet another signal for cold to dominate into early March.
The Bottom Line
A trend toward colder than average conditions is expected to redevelop this week with redevelopment of a strong western USA ridge and eastern USA trough couplet. A longer term negative trend in the Arctic Oscillation, in wake of continued disturbance of the Polar Vortex, suggests that colder than average weather conditions will likely dominate March.
More arctic outbreaks and snow is likely in coming weeks, set against rising sun angles and longer days, to extend Winter 2015-16 ( sorry Mr. Groundhog )!