022916 Forecast

My Forecast For Today ( February 29 )

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.

High Knob Massif Webcam
High Knob Massif Webcam – University Of Virginia’s College At Wise

Afternoon temperatures varying from chilly 40s atop the High Knob Massif to the mid-upper 50s in Norton-Wise and adjacent plateau-ridge communities.

Nora 4 SSE
Nora 4 SSE – National Weather Service Site In Middle Elevations

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.

Updated Storm Prediction Center Risk Region
Updated Storm Prediction Center Risk – 7 AM Tuesday to 7 AM Wednesday
Storm Prediction Center Discussion
Storm Prediction Center Discussion

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. 
NAM 4 KM Model
NAM 4 KM Model Total Precipitation Forecast Next 60-Hours

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.


My Overnight Discussion

Reference February 2016 Majesty In High Knob Massif for a set of photographs and information detailing this recent winter storm.
Rime Capped Beauty of High Knob Massif
Rime Capped Beauty of High Knob Massif – February 27, 2016

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.

Lonesome Pine Airport In Wise
Lonesome Pine Airport In Wise

SW wind gusts of 30 to 50 mph have been common across the area this evening into the overnight.  ROARING winds.

Black Mountain MesoNET Wind Graph
Black Mountain MesoNET Wind Graph

Wind speeds began increasing at upper elevations during early afternoon, with downward mixing and lowering of strong and gusty winds into the evening.

Flatwoods Mountain MesoNET Wind Graph
Flatwoods Mountain MesoNET Wind Graph

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.
Nora 4 SSE
Nora 4 SSE – Site Of Official NWS Station In Middle Elevations

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.

NASA Infrared Satellite Image
NASA Infrared Satellite Image At 12:30 AM on February 29, 2016
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.
NASA IR Image With Approximate
NASA IR Image With Approximate Stationary Wave Axis At 1:30 PM – Feb 29
*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.

NAM 12 KM Model 300 MB Forecast
NAM 12 KM Model 300 MB Forecast At 1:00 AM Wednesday – March 2, 2016
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.
NAM 12 KM Model 925 MB Forecast
NAM 12 KM Model 925 MB Forecast At 1:00 AM Wednesday – March 2, 2016

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.

NAM 12 KM Model 500 MB Vorticity Forecast
NAM 12 KM Model 500 MB Vorticity Forecast At 1:00 AM – March 2, 2016
Storm Prediction Center Severe Risk
Storm Prediction Center Severe Risk From 7 AM Tuesday to 7 AM Wednesday

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.

Storm Prediction Center Day 2 Discussion
Storm Prediction Center Day 2 Discussion

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.

Have a great Monday.