Mountain Area Forecast ( March 19-21 )

ALERT For A Significant Winter Storm Event For Late Tuesday Night Through Wednesday Night – Especially At Middle To Upper Elevations 

Deep moisture associated with a developing upper level low will redevelop precipitation through Tuesday evening with a transition to snow from top to bottom beginning during the 8-11 PM time period Tuesday.  Snow levels will drop in elevation to Norton-Wise during the overnight and reach valley floors below 2000 feet, along and north of the High Knob Massif-Tennessee Valley Divide, by Wednesday AM.

A deformation snowband and comma-head swirl will keep snow over the area through Wednesday evening into early hours of Thursday, with a possible mix during the day at lower elevations below 1500-2000 feet.

Total Snowfall Forecast
Tuesday Night-Thursday AM

*Lower Elevations – Below 2000 Feet
1″ to 3″

Middle Elevations – 2000 to 3000 Feet
2″ to 6″

Upper Elevations – Above 3000 Feet
4″ to 8″ with locally higher amounts – especially within the High Knob Massif and along the much more narrow crest lines of Black Mountain

Many valleys within the High Knob high country are higher than Pine Mountain, such as within the High Knob Lake and Big Cherry Lake basins where valley floors are higher than the highest peak on Pine Mountain in Dickenson County ( 3149 feet at Birch Knob of Pine Mountain ).  Therefore, I mainly group Pine Mountain in with the Middle Elevation Zone given only a few small peaks rising above 3000 feet along its 120 air mile extent.

The Pine Mountain crest actually becomes lower than the Wise Courthouse southwest of Harlan County in southeastern Kentucky.  Pound Gap of Pine Mountain, at 2372 feet, is about the same as the City of Norton Water Plant and is also lower in elevation than the Wise Courthouse ( 2454 feet ).

Target Snowfall 4.0″ in Norton-Wise ( +/- ) 2″ error potential.  This implies potential for 2″ to 6″ of snowfall during the period.  MAX snow depths on the ground will likely be near to LESS than total snowfall amounts in most locations.

*Snow accumulations of 1″ or less are generally expected at elevations below 1500 feet, except within upslope locations along and north of the High Knob Massif and Tennessee Valley Divide where air will be rising and cooling.

While Power Outages will be a MAJOR Threat in central and northern Virginia into West Virginia, the local risk will be more limited but not non-existent.  Lower density snow at upper elevations, in colder air, will help to lower the risk where heaviest snow falls above 3000 feet.  The middle elevation zone, between 2000 and 3000 feet, will possess the highest local risk of power outages.  Ultimately, this will be determined by how much snow accumulates.

Reference my Mesoscale Discussion below and stay tuned for updates which may need to be issued once the banding features develop.  Deep moisture will generate widespread snow ( not a snow shower type of setting ) and areas that generate low-level convergence will help form mesoscale bands of heavy snow embedded within the larger snowfall field.  That is the proper way to approach a system like this.

*A snow shower-flurry setting develops only toward the end of this system as the vertical moisture profile becomes less and the snowfall producing moisture become relegated to lowest levels.  So this should be forecast as snow, with locally heavy bands.

Although beneath a developing upper-level low, temperatures aloft over the mountains will be 20-30 degrees Fahrenheit higher than last week’s intense snow squall setting.  So this will not be a setting favorable for snow bursts, instead any heavy snow of that nature will more likely be associated with a mesoscale band outside of orographic lifting zones.  

Overnight Into Monday Morning

Increasing clouds.  Winds SSW-SW at 5-15 mph with higher gusts along mid to upper elevation mountain ridges.  Temps varying from 30s in mountain valleys to the 40s on exposed ridges and plateaus.

Monday Afternoon

Mostly cloudy.  A chance of showers, thunder possible, toward sunset. Winds becoming SE to SSE at 5-15 mph with higher gusts.  Temperatures varying from low-mid 50s at upper elevations to the 60s ( warmest downslope sites of northern Wise and Dickenson-Buchanan counties with upper 60s to around 70 degrees. ).

Monday Night Into Tuesday Morning

Rain with a chance of thunder.  Local downpours.  Winds SE to SSE at 5-15 mph, with higher gusts, below 2700 feet.  SSE to SSW winds 10-20 mph, with higher gusts, on mountain ridges above 2700 feet.  Temperatures in the 40s to around 50 degrees.  Areas of fog, widespread and dense at upper elevations in upslope locations of the High Knob Massif.

Tuesday Afternoon

Rain with a chance of thunder.  Local downpours.  SSE winds at 5-15 mph, with higher gusts, shifting to SW by late.  SSE-SW winds 10 to 20 mph, with higher gusts, along mountain ridges above 2700 feet.  Areas of fog, dense and widespread at upper elevations ( orographic cap clouds ).  Temps in the 40s upper elevations and in the 50s at low-mid elevations, dropping by late afternoon.

Tuesday Night Into Wednesday Morning

Rain changing to snow from top to bottom.  Snow may be heavy at times.  Winds SW-W at 10 to 20 mph with higher gusts.  Temps falling into the 20s to lower 30s ( around 20 degrees on highest peaks ).  Low cloud bases with rime formation at upper elevations.  Wind chills dropping into 10s and 20s, except single digits at highest elevations.

Wednesday Morning Through The Afternoon

Snow.  Snow will be heavy at times.  Snow may mix with rain at lower elevations, especially below 1500 feet and to the south and southwest of the High Knob Massif and the Tennessee Valley Divide.  WNW-NW winds 10-20 mph with higher gusts.  Temperatures varying from 20s in the upper elevations to the mid 30s.  Wind chills in the 10s and 20s, except locally colder in gusts at highest elevations.  Rime formation at highest elevations.

Wednesday Evening Into Thursday Morning

Snow.  Snow may be heavy at times during the evening before tapering off to snow showers and flurries into the overnight.  Winds WNW-NNW at 5-15 mph, with higher gusts.  Temperatures varying from the upper 10s to the upper 20s ( coldest at highest elevations ).  Wind chills in the 10s & 20s, except 0 to 10 degrees highest elevations.

A very stormy pattern is looking to dominate the next 1-2 weeks, with potential for heavy to excessive precipitation currently being monitored into next week.

Reference Wintry Transition In March 2018 for a recap of changing conditions during the first half of this month.

 

Weather Discussion ( More Winter )

Mesoscale Discussion

( Tuesday Afternoon Update )

A complex system will be developing right over top of the mountain area in mid-upper upper levels in coming hours, with an influx of colder air aloft helping to change rain into snow from top to bottom over time ( changing first at the summit levels of the High Knob Massif & Black Mountain ).

Being beneath an upper level low can always offer several complications, and this setting will likely be no different as pieces of energy swirl around the low to help develop areas of enhanced ( mesoscale ) snowfall.

Models are initially wanting to develop the heaviest snow along a low-level convergence field where westerly and easterly air flow trajectories will be coming together.

Convergence initially in the High Knob Massif area shifts to the northeast and east.  Note easterly 850 MB streamlines to the northeast into southern West Virginia and central parts of Virginia ( below ) at 11:00 PM Tuesday evening.  Easterly flow across central-northern Virginia is coming off the western Atlantic Ocean to advect or transport the best moisture for heaviest snowfall development.

By Wednesday morning ( below ) the convergence line is still forecast to be across central Virginia & West Virginia, and the heaviest snow should occur from that area north-northeast into Pennsylvania.  Other areas with moderate to heavy snow, of lesser extent, will be along the windward slopes of the Cumberland Mountains & Blue Ridge in the southern Appalachians ( where air possessing a westerly component will be lifted ).

The setting for heavier snow actually improves locally during Wednesday afternoon into Wednesday evening as the deformation band shifts southeast and the low-level flow becomes more WNW-NNW ( NW ) and orographic forcing increases into the Cumberland Mountains.

Deep moisture + significant orographic forcing will produce moderate to heavy snowfall, with worst conditions likely to develop in this area during late Wednesday afternoon into the evening hours ( especially around and after sunset ).

The coldest air will be developing along the western side of the 850-700 MB lows, which will help lower snow density at upper elevations ( this will also add some fluff factor such that this could help increase snow amounts and is a wild card factor in this system ).

 

Previous Discussion

Following the first strong to locally severe thunderstorms of Meteorological Spring the pattern will be transitioning back into a wintry mode in coming days as part of what is looking like an increasingly stormy early spring regime.

Although thunderstorms will become possible later Monday into Tuesday, the severe risk is currently forecast to remain southwest of the mountain area as another Miller Type B cyclone develops across the region.

Central-southern Tennessee will be under the gun for a possible outbreak of severe thunderstorms.  This will need to be closely watched into Tuesday.

Colder air will begin to flood into the area Tuesday night into Wednesday morning, with a change to snow from the highest elevations downward over time.  Trajectories of air flow will be important to initial accumulations before a change into NW flow occurs, so stay tuned for updates.