Mountain Area Forecast ( Feb 5-8 )
ALERT For Slick Patches Developing On Roadways With Dropping Temperatures Wednesday Evening
Caution is advised for those planning to travel through Wednesday Night with a combination of dropping temps and upslope snow showers and flurries.
ALERT For High Water Levels Along Creeks Draining The High Knob Massif Into Thursday Morning ( Feb 8 )
The combination of significant rain and melting snow has pushed stream levels above flood stage in local areas, with ROARING whitewater along creeks draining the High Knob high country along both sides of the Wise-Scott border.
The Big Stony Creek stream gauge in northern Scott County crested 0.7 feet above flood stage, the highest level observed in 2018, and is expected to begin declining Wednesday evening as below freezing air increases and the freezing level drops.
Although snow cover continues to be solid across northern slopes at upper elevations, and patchy on south slopes, and air temperatures have now dropped below freezing again at upper elevations, run-off will maintain high but declining levels on creeks through Wednesday night.
Strong Rises On Creeks, Especially Those Draining The Snow Covered High Knob Massif, Will Become Possible By Wednesday Afternoon
A live view from Eagle Knob of the High Knob Massif shows that clouds are engulfing upper elevations. Air temperatures have been below freezing all day until recently, with a climb to around and just above 32 degrees.
Substantial snow covering upper elevations across Black Mountain and the High Knob Massif will be melting with significant rain and dense fog into Wednesday.
People living along creeks draining the high country will need to remain ALERT for strong water level rises during Wednesday before colder air returns to diminish run-off.
Alert For Strong SSE-SW Winds Developing During Tuesday Night Into Wednesday Morning
A tightening pressure gradient in advance of significant rains will generate strong winds at mid-upper elevations, beginning first in upper elevations and working downward through middle into the lower elevations ( especially locally where mountain waves form ) during Tuesday night into Wednesday morning.
Overnight Into Tuesday Morning
Increasing and lowering clouds overnight into morning with a small chance of light snow or mixed precipitation. Windy across higher mountain ridges. Winds S-SW at 5-15 mph with higher gusts on mountain ridges-plateaus below 2700 feet. Winds SW-WSW 15-25 mph, with higher gusts, on mountain ridges above 2700 feet. Temps varying from 20 to 25 degrees to around 30 degrees, tending to rise overnight into morning. Wind chills in the 10s and 20s, except single digits along highest mountain ridges.
Mostly cloudy. Chilly. Generally light & variable winds. Temperatures in the 30s to lower 40s ( struggling toward freezing at highest elevations ). Wind chills in the 10s to lower 20s at highest elevations.
Tuesday Night Into Wednesday Morning
Rain developing. Becoming windy. Rain may be heavy at times overnight into morning. A chance of thunder. SSE to S winds 10-20 mph, with higher gusts, on mountain ridges-plateaus below 2700 feet. Winds S-SSW 20-30 mph, with higher gusts, on mountain ridges above 2700 feet. Temps near steady or slowly rising from the 30s to low-mid 40s. Areas of dense fog, especially at upper elevations. Wind chills in the 20s and 30s. Nasty!
Wednesday Morning Through The Afternoon
Rain, heavy at times, tapering to showers and drizzle. Turning colder. Rain changing to snow showers or to freezing drizzle at by late afternoon. Widespread dense fog at higher elevations. SW winds shifting NW at 5 to 15 mph with higher gusts. Temperatures falling back through the 30s ( into 20s at upper elevations by mid-late afternoon ). Wind chill factors dropping into 10s & 20s ( coldest at highest elevations ).
Wednesday Night Into Thursday Morning
Low clouds. Turning colder with snow showers & flurries. Snow accumulations mainly less than 1″, with some locally higher amounts possible. Winds WNW to NW at 5-15 mph, with higher gusts. Temps dropping into the low-mid 10s to low-mid 20s ( coldest at highest elevations ). Low clouds with rime formation at upper elevations. Wind chills dropping into the 10s to lower 20s, with single digits at upper elevations.
Hydrologic Outlook – A Heavy To Excessive Rainfall Pattern Will Be Developing From This Weekend Into Next Week. Please Stay Tuned For Later Updates.
A Watch For A Major Arctic Outbreak Impacting The USA May Be Needed Within The Next Week To 10 Days ( refer to my weather discussion section for more details ).
Weather Discussion ( Volatile Pattern )
Wednesday Afternoon Update
Falling temperatures ( 20s as of 5 PM at upper elevations in the High Knob Massif ) is causing a relatively rapid drop in freezing levels. This is good to help reduce run-off where creeks draining the High Knob Massif are simply ROARING. On the other hand, this is bad news since it will generate slick patches on area roadways.
Main concerns through Wednesday evening center around the possibility of slick conditions developing with freezing of moisture on roadways ( State Route 619 is already getting slick at highest elevations ), so caution is advised for those traveling, as well as for those who may live or be around the high water levels on creeks draining the massif along both sides of the Wise County-Scott County border.
The most exciting period of Winter 2017-18 is upcoming, with a highly volatile pattern taking shape across the Northern Hemisphere through the next few weeks.
Really the excitement has already been observed, with up to 5″ of new snow falling at the summit level of the High Knob Massif during the predawn-morning hours of Sunday.
Conditions were wicked, with air temps in the low-mid 20s and strong S-SW wind gusts over 30 miles per hour. Snow continued into mid-morning before changing to freezing rain and then rain.
Layton Gardner reported around 1″ of snow at his station near Lonesome Pine Airport, while I measured only 0.5″ in Clintwood as snow became mixed with sleet and freezing rain before changing to rain.
Heaviest snow in valleys actually fell along the windward side of the High Knob Massif with respect to S winds, with a corridor from the Duffield Valley to Fort Blackmore picking up significant snow as air was being forced to rise upward over not only the massif but an orographic standing wave which developed along the high country.
Although temperatures aloft were going above freezing to cause snow to transition to sleet, freezing rain, and rain in all locations surrounding the High Knob Massif in far southwestern Virginia, the formation of an orographic wave over & along the windward side of the massif forced air upward and over the wave, with this rising generating enough cooling to overcome the transport of warming air at and above the 875-825 MB layer.
Like water rolling off a breaking ocean wave approaching the beach, air was sinking upon crossing the wave crest and high country to generate a change into mixed precipitation toward Wise and Clintwood ( which received significantly less snow than Duffield and places on the Clinch River, in northern Scott County, which tend to be robbed of snowfall when air is flowing out of WNW to NE directions ( and sinking down off the high country ).
A majestic sun dog, formed by the refraction & scattering of light through high altitude ice crystal clouds, produced a rainbow of beautiful color above UVA-Wise Monday afternoon.
The second part of this system, which appeared to be the easiest to forecast, actually ended up producing much less NW flow snow than predicted. Joe Fields measured 0.5″ of new snow in the High Chaparral community, with around or just over 1″ on Eagle Knob, while much of the area had only a dusting. Roads were still slick with freezing from lingering moisture and what little snow that did fall.
Deposition of cloud vapor ( below ) added to moisture in the high country where riming, as so often occurs, developed once again in sub-freezing air. Deposition releases 680 calories of heat energy per gram into the atmosphere, so despite such cold conditions the process of rime formation is actually exothermic in nature and releases heat into the air ( perhaps a warming thought to keep in mind the next time you are up there and think “something” is just going to drop off your body in this dang cold air!!! ).
Now attention turns toward another nasty looking system which will spread significant rain across the mountain area Tuesday Night into Wednesday as a band of heavy snow sets up along and north of the Ohio River.
A local concern is a significant amount of snow ( as noted above ) on the ground across the high country, with depths generally varying from 2″ to 3″ on southern slopes at the 3000 to 3300 foot level to 4″-8″+ above 3300 feet on north slopes and at highest elevations ( all slopes ). The water content of this snowpack has had time to build, with the bottom oldest snow layer having been deposited during January 29-30 ( so rime + rain has been added over time ).
Snow is deep enough to absorb quite a bit of rain and the melt period will be somewhat less than 24-hours before temperatures drop below freezing again. Dense fog vapor, within orographic clouds; however, is always a concern.
*Latent heat of condensation can be a powerful agent applied to melting, so this situation will bear close watching with respect to run-off on Wednesday.
Latent heat of condensation releases 600 calories of heat energy per gram of water to the atmosphere. In this case a combination of orographically forced rising of air and the movement of milder air across the cold, snow will generate latent heat release via condensation in the air and at the surface of the snowpack. Rapid snow melt can occur in such cases.
Some energy; however, is absorbed at the same time, around 80 calories per gram, in the melting process to offset a little of the latent heat that is released with condensation at the snow surface.
Total precipitation in this area has been significantly above locations toward the south in the Tri-Cities, with January 1 to February 5 totals of 5.35″ at the City of Norton WP and between 6.00″ to 7.00″ across the High Knob high country versus 2.57″ measured officially at TRI ( Tri-City Airport ).
This gorgeous photograph by my friend Wayne Riner shows as much snow on the ground across the Apple Orchard as the TRI officially has measured so far during the 2017-18 winter.
Snowfall atop the High Knob Massif has been 10 times greater than down in the TRI just since January 1 ( 30″ versus 3″ ).
Another system with potential to tap into a stronger feed of Gulf Moisture is expected by this weekend so elevated water level concerns may increase in the mountains. It is all part of what is shaping up to be a volatile weather pattern.