Alert For Slick Road Conditions Developing At Middle To Upper Elevations During The Predawn-Morning Of Thursday ( March 8 ) – Possible Slick Conditions At Lower Elevations Along & North Of The High Knob Massif-Tennessee Valley Divide
A Hit Or Miss Snow Squall ( Burst ) Potential Will Exist During Thursday Afternoon-Early Evening
A vigorous upper air disturbance and pocket of very cold air aloft will begin to generate snow showers during the early to middle overnight period of Wednesday. Bursts of heavy snow are expected by the predawn-morning to impact the morning commute.
A more scattered array of flurries and snow showers, with some mix or rain at lower-middle elevations, will be possible into the afternoon hours of Wednesday.
Additional accumulations will be possible at all elevations, especially along and north of the Cumberland Front, during the overnight-morning hours of Thursday. Bitterly cold wind chills will be a definite factor during this period.
Monday Morning – A large vertical temperature spread will greet the dawn under ideal cooling conditions, with temps varying from frosty 10s to lower 20s in colder mountain valleys to the 30s across exposed mid-upper elevation mountain ridges and plateaus.
5:00 AM Monday – A temp of 23 degrees in Clintwood, with 10s at upper elevation valleys in the High Knob Massif to contrast with middle 30s along highest ridges.
Monday Afternoon – Expect increasing mid-high altitude clouds in advance of the next weather system. Temps are expected to rise into the 50s, with 40s at upper elevations, amid light & variable winds.
Monday Night Into Tuesday Morning
Increasing & lowering clouds. A chance of rain showers by morning. S-SW winds increasing to 5-15 mph, with higher gusts, along mid-upper elevation mountain ridges-plateaus.
Tuesday Afternoon
A chance of rain showers, then becoming partly cloudy by mid-late afternoon. SSW-WSW winds 5-15 mph with higher gusts. Temperatures varying from the 30s to low 40s at the upper elevations to the upper 40s to low 50s.
Tuesday Night Into Wednesday Morning
Increasing clouds with flurries, snow showers, and snow squalls developing. Locally heavy bursts of snow. WSW-WNW winds increasing to 10-20 mph, with higher gusts. Temperatures dropping into the low-mid 20s at highest elevations to the lower 30s.
Wednesday Afternoon
Mostly cloudy. Windy. A chance of flurries & snow showers. WNW winds 10-20 mph, with higher gusts. Temperatures varying from 20s at upper elevations to the 30s at middle to lower elevations. Wind chills in the 10s & 20s.
Wednesday Night Into Thursday Morning
Snow showers & flurries. Local bursts of snow developing overnight into morning. WNW winds 5-15 mph, with higher gusts, at elevations below 2700 feet. Winds WNW-NW 10 to 20 mph, with higher gusts, at elevations above 2700 feet. Temperatures dropping into the 10s at upper elevations and the 20s at lower-middle elevations.
Wind chills varying from -5 below zero to 10 above zero at the upper elevations, above 3000 feet, with 10s to near 20 degrees at lower-middle elevations. Rime formation at highest elevations.
Thursday Morning Through The Afternoon
Abundant clouds and mixed sun with snow showers, flurries and local squalls ( bursts of intense snow ). Windy and unseasonably cold. WNW-NW winds 10-20 mph, with higher gusts. Temps varying from 10s at highest elevations to upper 20s to middle 30s. Wind chills in the 10s & 20s, except single digits above-below zero at high elevations.
The potential for significant snowfall is being monitored for Friday Night into Saturday ( March 9-10 ) and again by late in the weekend-early next week.
The mountain area is stuck in a repetitive, cold pattern with another round of accumulating snow expected to occur into Thursday morning, much like observed into Wednesday AM.
High Knob Massif Webcam – University Of Virginia’s College At Wise
Wednesday morning snow varied from a dusting to around 1″ at upper elevations in the High Knob Massif and on Black Mountain ( along the Wise-Harlan County border ).
High Chaparral of High Knob Massif At 6:13 AM on Wednesday – March 7, 2018
This is what nurse Darlene Fields saw when see looked outside in High Chaparral Wednesday morning ( above ).
A burst of snow that covered roads and left slippery, cold conditions behind as it passed by sunrise ( below ).
Eagle Knob of High Knob Massif – A bitter 19 degrees at 8:40 AM ( March 7 )
This set the stage for a bitterly cold day in the high country, and pretty dang cold in the lowlands as well, with morning 10s that only reached low 20s on Eagle Knob. Wind chills as cold as sub-zero in stronger gusts put winter into the air!
The main difference Thursday ( March 8 ) is that the snow burst potential is going to be greater and not just restricted to the morning, but into the afternoon as the vertical lapse rate really increases with a pocket of -30 to -40 degree F below zero air passing overhead at around 18,000 feet.
While the limiting factor will be moisture, a vertical temp profile like this over mountainous terrain must always be respected with even limited moisture.
Previous Discussion
A wintry pattern is beginning to rule this first month of Meteorological Spring, in wake of the wettest February on record, and will kick into full gear during coming days.
High Knob Massif Webcam – University Of Virginia’s College At Wise
An interesting deck of orographic clouds have been capping the High Knob Massif through Tuesday afternoon, amid the dry slot of a very large mid-latitude cyclonic storm system.
It is like a wall of clouds, with high elevations being engulfed in what many might call dense fog, but this is actually clouds being formed by the process of adiabatic upslope flow as lower-level air is forced to rise, expand ( amid lower air pressure ), cool, and condense out its moisture into visible clouds.
Although the process releases 600 calories per gram of water that is condensed, air temperatures have hovered in the 30s to around 40 degrees with much lower wind chills making it feel like 20s to around 30 degrees ( especially in frequent gusts ).
High Knob Massif Webcam – University Of Virginia’s College At Wise
A Cody Blankenbecler image ( below ) shows what it looks like inside the orographic cloud ( like a dark, dense fog ).
Eagle Knob of High Knob Massif – Inside An Orographic Clouds – March 6, 2018
This occurred despite being within the ”dry slot” of a large middle latitude cyclonic storm, which fills the USA on this GOES-16 Mid-Tropospheric Water Vapor Image ( below ).
Air sinking downward from mid-levels of the troposphere forms a dry slot behind the surface cold front, as seen below with a yellow strip ( denoting dry air ) from West Virginia down along the TN-NC border that is sandwiched in between the frontal cloud band to the east and a large, cyclonic swirl of clouds to the west-northwest that is associated with the upper-level low ( comma-head ).
GOES-16 Mid-Level Water Vapor Image At 6:15 PM – March 6, 2018
This is a very energetic system, and that will become evident into coming days as periods of snow, some with intense, whiteout bursts, develop beneath very cold air aloft that greatly increase environmental lapse rates.
The above translated, means that any parcel or bubble of air rising upward from surfaces will remain warmer than the surrounding air and will continue to rise, accelerate upward. When super-imposed upon orographic lift this can enhance snowfall.
European Model 500 MB Height Anomalies At 7 AM Tuesday – March 6, 2018
While instability will be a most notable factor, intervals of more widespread, heavier snow ( especially along windward slopes of the Cumberland-Allegeheny Front and adjacent Blue Ridge spine ) will be triggered by periodic shortwaves, upper air disturbances, which will be moving through a longwave trough centered over the eastern part of the United States downstream of an upper level ridge centered over the Rockies and adjacent Plains.
Spring snowfall is notoriously hard to measure with best accuracy given sticking, melting, sublimation, settlement and other factors ( like wind ) that become enhanced by the increasing solar angle ( the distance traveled through the atmosphere by sunlight is decreasing as is the area covered by the sunbeam…that is, sunlight is becoming much more concentrated as the sun climbs higher above the horizon ).
A general 6-12″+ of snowfall, forecast between today and next Tuesday by ensemble model means, is looking likely for high elevations of the southern-central Appalachians; although, only the highest peaks will likely ever have that much on the ground at any given time…especially by later this coming weekend-early next week.
GFS Model Ensemble Mean Total Snowfall During The Next Week
At this time of year, especially, snow amounts will be decreasing with decreasing elevation ( but locations along the initial windward lifting zone will tend to have much more than locations along the secondary lifting zone ).
In this type of setting, the Cumberland-Allegheny Front is the primary lift zone with the Blue Ridge being the main secondary lifting zone.
A more concentrated low pressure system, tracking farther south, could alter zones of heaviest snowfall so stay tuned for later updates as this weekend-early next week system becomes more defined by models.
The Spring Equinox position of 0 degrees latitude is now fast approaching. This means that rays of sunlight will be directly overhead at the Equator on March 20-21, and the associated Circle Of Illumination will be tangent to the poles of the planet with all locations on Earth having approximately 12 hours of daylight and 12 hours of darkness ( just like during the Autumn Equinox ).
Longer days + more energy per unit of surface area means that snow is naturally harder to accumulate and maintain at this time of year, with higher, north to northeast facing slopes and hollows of the high country being most favored to accumulate and retain the greatest snow depths.
