Mountain Area Forecast ( March 29-30 )

Although The Threat Of Widespread High Water Has Decreased, Downpours Later Thursday Into Friday Should Still Be Monitored For The Possibility Of Localized Water Level Rises & Ponding

Overnight Into Thursday Morning

Mostly cloudy.  Mild.  S to SW winds 5-15 mph with higher gusts along mid-upper elevation mountain ridges-plateaus.  Temperatures in the 50s to near 60 degrees.

Thursday Afternoon

Mostly cloudy and unseasonably warm.  Chance of a shower or thunderstorm.  S-SW winds 10-20 mph with higher gusts. Temperatures varying from the low-mid 60s to the low-mid 70s ( coolest in upper elevations ).

Thursday Night Into Friday Morning

Showers & thunderstorms developing.  Downpours likely.  Gusty SW winds shifting NW-NNW at 5-15 mph, with higher gusts.  Turning colder overnight into morning with temps dropping into the 30s to mid-upper 40s ( coldest at upper elevations ).  Wind chills dropping into the 30s to low 40s, with 20s at highest elevations.

Friday Morning Through The Afternoon

Mostly cloudy, damp, and chilly with a chance of showers and drizzle.  Mixed precipitation or snowflakes possible at highest elevations.  Widespread low clouds-fog at the upper elevations.  Temps holding near steady or falling in the 40s at low-mid elevations, and the 30s at upper elevations, in locations along and north of the High Knob Massif and Tennessee Valley Divide.  Wind chills in the 20s & 30s.

An unsettled weather pattern is expected to continue into April with more significant precipitation likely amid the return of cooler than average conditions.

Weather Discussion ( Close Call )

Although some light showers have occurred during the past 24-hours, high pressure off the southeastern USA coast has been just strong enough to hold training batches of heavier rainfall west of the mountains in the Kentucky foothills.

One aspect not being under-estimated has been wind, with gusts topping 30-40 mph ( especially across upper elevations ) during the past several days & nights.  This has kept the atmosphere well mixed and relatively mild for late March.

Rather extensive snow continued to cover upper elevations in the high country, especially northern slopes, throughout March 27.

Downpours are still expected as the front approaches the mountains by Thursday Night into early hours of Friday, but duration of heavy rain should be limited within the maritime tropical air mass ahead of the cold front.

Given recent snow melt and wet conditions strong rises may still occur on streams, so please remain alert.

A modified cP ( continental Polar ) air mass will be pouring into the mountains Friday, and if low clouds hold tough the conditions will become extremely chilly with 30s and 40s in locations along and west-northwest of the Cumberland and Allegheny Front ( with colder wind chills ).

Mountain Area Forecast ( March 26-28 )

ALERT For Strong SSW To WSW Winds At Mid-Upper Elevations From Tuesday Through Wednesday

 A strengthening pressure gradient will support strong and gusty SW winds into the Cumberland Mountains, especially at higher elevations, from Tuesday through Wednesday.

Downpours In Showers And Possible Thunderstorms Will Become Likely Wednesday Through Thursday, In A Pattern Conducive To Training And The Orographic Enhancement Of Rainfall Along And Westward From The Cumberland Mountains

Those living and driving along creeks and in low-lying, flood prone locations will need to be alert for the potential of strong water level rises, especially in locations along and west of the Cumberland Front where orographic rainfall enhancement will be favored over already wet ground.

*Thursday ( March 29 ) is looking like the day with best support for heavy rainfall.  If rainfall amounts remain limited and west of the  mountains into Thursday it will help but not eliminate the threat.  Models currently disagree on how much rain will fall with this system, despite climatologically favored air flow trajectories.  

Overnight Into Monday Morning

Mostly cloudy.  Windy across mid-upper elevation ridges and exposed plateaus.  SE winds 10-25 mph, with higher gusts.  Temperatures varying from the upper 20s to the mid-upper 30s.  Winds chill factors in the 20s to low 30s, except 10s in gusts at highest elevations.

Monday Afternoon

Mostly cloudy.  Gusty.  Winds SE-S at 5-15 mph with higher gusts.  Temperatures varying from the mid 40s to the mid-upper 50s ( coolest upper elevations and warmest within downslope locations along & northwest-north of the High Knob Massif and Tennessee Valley Divide ).  Wind chills in the 30s at the highest elevations.

Monday Night Into Tuesday Morning

Mostly cloudy.  Chance of rain showers.  Windy.  SE-S winds at 10-20 mph, with higher gusts, along mountain ridges and plateaus below 2700 feet.  SSE-SW winds 15-30 mph, with higher gusts, on mountain ridges above 2700 feet.  Temps varying from the mid-upper 30s to mid-upper 40s.  Wind chills in the 20s and 30s ( coldest at highest elevations ).

Tuesday Afternoon

Mostly cloudy.  Chance of rain showers.  Windy.  S-SW winds 10 to 25 mph with higher gusts.  Temperatures varying from the upper 40s to lower 50s in upper elevations to the upper 50s to lower-middle 60s ( warmest in downslope locations of northern Wise and Dickenson-Buchanan counties ).

Tuesday Night Into Wednesday Morning

Mostly cloudy.  Rain showers becoming likely.  Windy.  SSW-SW winds 10-25 mph, with higher gusts, on mountain ridges and plateaus below 2700 feet.  SW-WSW winds 20-30 mph with higher gusts on mountain ridges above 2700 feet.  Temperatures in the 40s to lower 50s.

Wednesday Morning Through The Afternoon

Showers with a chance of thunderstorms.  Downpours possible.  SW winds 5-15 mph with higher gusts.  Temps widespread in the 50s to lower 60s.

A colder than average pattern is being monitored for the first week of April, with the potential for more significant precipitation as winter-spring air masses continue to clash.

Weather Discussion ( Lion In & Out )

Monday Night Update

A flow pattern conducive to significant rainfall amounts is being highlighted during mid-late week.  The good news is that the system will be progressive, the bad news being this type of flow is climatologically favored to generate rainfall amounts which are moderate-heavy over very wet ground.

Creeks are running strong and some snow is yet to melt at highest elevations, but mostly the February-March period has been very wet with locally more than 20.00″ of total precipitation.

The forecast low-level streamline pattern fits annual climatology = inflow into the Cumberland Mountains from the Gulf of Mexico with orographically enhanced rainfall amounts on rising air flow trajectories.  Here is where the pattern is forecast, not any given model prediction of rain amounts.  Past climatology, a powerful tool, of similar type settings signals that significant rainfall amounts will be possible to likely from Wednesday through Thursday.

Upper air dynamics add to low-level orographics by Thursday to continue and enhance the threat for heavy rain with showers and moisture lifting northeast from storms to the southwest ( the local setting does not look favorable for strong-severe thunderstorms which is also good ).  If it were not for so much antecedent precipitation during the past 8 weeks this system would not be as much of a concern.

*Although FFG ( Flash Flood Guidance ) is a useful tool, it must be recognized that input precipitation values are typically under-estimated for orographic locations; therefore, high water issues often arise quicker during such wet antecedent conditions than FFG values indicate.  The terrain is three-dimensional, complex and is not fully resolved by models, which is where the human factor must come in to improve these model short-comings.

This is not a prolonged flood threat, with the system now expected to clear the area Friday into Saturday, but is one that should not be taken for granted with orographics to be given their proper respect.

Meanwhile, winds are already ROARING at elevations around and above 2800 feet, so caution is advised tonight through Wednesday as tree or tree limb damage may occur due to recent wetness and winter storms.

Previous Discussion

Although weather conditions may improve by the final hours of March 2018, a setting favorable for more heavy precipitation could push monthly totals into ( or very close to ) double digits for the second consecutive month at the upper elevations in the High Knob Massif.

March 2018 precipitation totals of 6.00″ to 7.00″ have been observed at upper elevations in the High Knob high country in wake of this latest winter storm event that left significant ice accumulations and snow ( 3-5″ of new snow above 3000 feet ).

Snow depths decreased substantially in the high country into the morning hours of Sunday with freezing rain-rain, dropping from max depths ( including old snow ) that reached 3″ to 12″++ prior to the precipitation type change on Saturday afternoon.

Deepest depths of new snow occurred in the early afternoon of Saturday ( March 24 ) when a transition to rain & freezing rain occurred.  A general 3″ to 5″ was widespread along and north of the High Knob Massif and Tennessee Valley Divide, with locally less ( to none ) where E-SE air flow downsloped off the high country into the Powell Valley-Big Stone Gap corridor of Wise County.

Snow was so heavy that sticking began in Clintwood with air temperatures above freezing, as snow fell faster than it could melt ( with large flakes ).  Roadways became covered at elevations below 1500 feet to the north of the Tennessee Valley Divide versus rain at similar elevations to the south.

Sunday morning GOES-16 imagery showed both the narrow nature of the system snow band, as well as a striking local contrast between sunshine atop the High Knob Massif and a deck of low clouds banked up along and north of the massif.

The focus now shifts to a pattern favorable for heavy to excessive rainfall, especially in locations along and west of the Cumberland-Allegheny Front and Cumberland Plateau during the March 29-31 period with a tropical fetch of deep moisture from the Pacific Ocean and Gulf of Mexico ( along and in advance of a strong cold front ).

A return to a colder flow may arise by this weekend and the first week of April, following significant rains and possible thunderstorms.

Since this is an evolving and changing pattern, stay tuned for updates as models better resolve the potential wetness of the atmospheric river of moist air expected to impact the region from the Appalachians to Mississippi River Valley.

250 MB Jet Stream Flow Field

Observe the long flow field across the Pacific Ocean into the United States, which is already beginning to be joined by a 850 MB flow from the Gulf of Mexico along the Mississippi River Valley.

850 MB ( Around 5000 feet ) Flow Field

Mountain Area Forecast ( March 23-25 )

Updated: 7:50 PM on March 24

ALERT Continues For Icing With Freezing Rain At High Elevations In The High Knob Massif – Mixed With Snow – With An Ice Storm In Progress

Note: High traffic volume is making the website slow today, so be patient.

*A notable increase in ice accumulation is occurring.

An all out ice storm is in progress in the high country with the potential that the freezing level will drop as 925-875 MB winds back more E-ENE during the evening to also impact communities near and above the level of Flat Gap.

Trees & power lines have started to droop under increasing weight of ice forming at upper elevations in the High Knob Massif, with worst icing above 3300 feet ( note ice & icicles on chain link fence on Eagle Knob ).  Snow continues to be mixed during periods of heavier precip ( bright banding on Doppler often indicates this ).

Travel along State Route 619 and Routes 237, 238 and others at the upper elevations is discouraged.  Travel along Route 237 has been nearly impossible and restricted to high profile 4×4 vehicles.

At middle to lower elevations along and north of the High Knob Massif temperatures are marginal in colder locations, with 32.7 degrees officially in Clintwood as of 8:00 PM.

ALERT For Areas Of Very Dense FOG Through Saturday Evening Into Early Hours Of Sunday ( March 25 )

Although clouds ( dense fog ) have been widespread at upper elevations throughout Saturday, an increasing concern through Saturday Night will be reduced visibility within areas of very dense fog at middle-lower elevations.  Locations with snow cover will have some of the worst fog.

ALERT For A Slower Than Expected Change From Snow To Rain In Wise & Dickenson Counites – Power Outage Potential Increasing

As of early Saturday PM a general 3″ to 5″ of wet snow had accumulated across much of Wise and Dickenson counties, with a slower than expected change.  Despite temperatures within the lower 30s snowfall  has been heavy enough to accumulate.  Mixed sleet has also occurred.  Should this continue it will greatly increase risk of power outages.

*Due to sinking air off the High Knob high country on SE flow the amount of snow drastically decreases to the southwest toward Powell Valley and Big Stone Gap.

The atmosphere has become nearly isothermal through a deep layer.  It is hoped that afternoon rises will help deter this increasing threat and that these counties will not have to be added into the region facing a crippling fall of snow.

The Heaviest Precipitation Is Yet To Come Into Late Saturday and Saturday Evening and the form it takes will determine how critical this situation becomes.  A change to rain is still being predicted by models even though it has been very slow to occur. 

ALERT For The Potential Of A Crippling Fall Of Wet Snow Across Eastern Portions Of Southwest Virginia Within A Corridor Between Marion And Martinsville, Centered Upon The Greenbrier And New River Basins

Travel into eastern portions of southwestern Virginia is expected to become hazardous during Saturday, with the potential for a crippling fall of wet snow.  Travelers who plan on attending the NASCAR races in Martinsville should be aware that travel along I-81 and Route 58 could become impossible during the climax of this event.

Overnight Into Friday Morning

Partly-mostly clear.  Cold.  WNW-NW winds 5-15 mph with some higher gusts along middle-upper elevation mountain ridges.  Temperatures dropping into the 20s, with 10s to low 20s in coldest upper elevations sites.  Wind chill factors in the 10s & 20s, except single digits along highest mountain ridges at upper elevations.

Friday Afternoon

Mostly sunny, with increasing high clouds by mid-late afternoon.  Seasonally cold.  NW winds 5-15 mph, with higher gusts.  Temperatures varying from 30s at upper elevations to the mid 40s to lower 50s.

Friday Night Into Saturday Morning

Increasing clouds.  Snow developing during the predawn hours, possibly beginning as a mix or rain, especially to the southwest and south of the High Knob Massif.  Variable winds generally less than 10 mph.  Temperatures falling into the upper 20s to lower 30s.

Saturday Morning Through The Afternoon

Morning snow or mixed precipitation giving way to rain.  Rain may be heavy at times.  Cold & nasty.  Freezing rain with significant icing possible in the High Knob Massif.  Winds SE-SSE at 5-15 mph, with higher gusts, at elevations below 2700 feet.  SSE-SSW winds 10-20 mph, with higher gusts, on mountain ridges above 2700 feet.  Temperatures hovering into the 30s to around 40 degrees ( 30-33 degrees in the High Knob Massif ).  Areas of dense fog, widespread at the upper elevations.

Saturday Night Into Sunday Morning

Evening rain giving way to overnight showers-drizzle.  Freezing rain at upper elevations in the High Knob Massif with a chance of freezing rain at colder mid-low elevation sites.  SE-SSE winds shifting ESE-ENE at 5-15 mph with higher gusts.  Temps in the 30s.  Areas of dense fog.

A setting favorable for heavy to excessive precipitation continues to be monitored for next week.  Please stay tuned for later updates on a stormy pattern to close March 2018.

Weather Discussion ( Nasty Pattern )

Saturday Afternoon Update

What is arguably the most sloppy ( NASTY ) system of the entire 2017-18 Winter Season has produced essentially all precipitation types across the mountain area today, with a significant amount of snow and icing.

850 MB Streamlines Showing Air Mass Clash ( March 24 )

A clash between air masses with mT ( maritime-tropical ) and cP ( continental polar ) characteristics is creating havoc across the region today as seen on current GOES-16 images.

A looming and potentially MAJOR weather maker is also already clearly visible on this image, a large river of atmospheric moisture streaming across the Pacific Ocean into the western-southern USA.  This will set the stage for what could be a heavy to excessive precipitation event next week.

250 MB Jet Stream Flow Across Pacific Into USA

Given significant snow depths-water content at upper elevations now, and observed water flow during Friday, this needs to melt and flush out of drainage basins of the Clinch, Powell, and adjacent Cumberland before any such system develops.

Late Friday Evening Update

Portions of Route 237 ( between High Knob and Big Cherry Lake ) continued to be covered by snow-ice late on Friday, March 23, with large snow drifts remaining along high crest lines. 

A significant weather event is expected to develop across southwestern Virginia during Saturday, with a nasty array of weather conditions.

While temperatures aloft will dictate major precipitation types, low-level temperatures will also be locally critical.

Adiabatic upslope cooling into the high country along the Wise-Scott-Lee County border may require an ICE Storm Warning ( the Wise-Harlan County border may also be impacted, but with less severe conditions ).

Following morning snow or mixed precipitation most of the area is currently expected to change over to a cold rain, but temperatures will remain unseasonably cold and it could be a close call for many locations.  Stay tuned for updates that may be needed as this system develops.

Previous Discussion

Sunshine during a TGIF should be savored as a truly nasty setting develops into this weekend as another significant precipitation event unfolds.

March 22 began with stacked lenticular clouds above the rime capped crest zone of the High Knob Massif.

Snowfall Totals & Ground Depths
( As of Morning of March 22 )

Clintwood 1 W: 1.3″
1″ ground depth
( 0.84″ event total )

Nora 4 SSE: 2.6″
1″ ground depth
( 0.97″ event total )

City of Norton Water Plant: 3.0″
2″ ground depth
( 1.28″ event total )

High Chaparral: 3.5″
( 2-3″ ground depth )

High Knob-Eagle Knob: 7.0″
( Variable depths with 1-2+ feet drifts )

This event continued to accentuate the wetness of 2018 with more than 2.00″ of total water equivalent precipitation falling during the March 16-22 period at Big Cherry Lake Dam ( 4.86″+ in March and 24.71″+ since January 1 ).

Snowfall and snow depths generally came in on the lower end of my forecast spread with this most recent event.  The exception being at upper elevations in the High Knob Massif between Bowman Mountain and the Thunderstruck Knob of Powell Mountain, where up to 7″ or more of snow fell.

Although a mixture of clouds and snow were present, there was no mistaking the outline of the High Knob Massif as it stood above the horizon of far southwestern Virginia on morning GOES-16 satellite imagery ( above ).

A thin layer of orographic clouds were forming along the summit of the massif at the time of the GOES-16 image, as viewed from the UVA-Wise Webcam above, and with motion were observed to be part of standing waves through which the air passed as it flowed southeastward toward the TRI.

The main focus now shifts to the next system which will be a wet one, with generally good model agreement on a well defined corridor of moisture; although, total amounts of precipitation remained varied.

Thursday evening ( 00 UTC ) runs of both the NAM and GFS models shifted more toward the ensembles of the GFS and European Model with respect to placement of the main axis of this precipitation corridor.

Models remain in considerable disagreement as to how much cold air deep enough to support snow will remain in place; therefore, they diverge on potential amounts.

The axis of the snowband is similar on both models during this run, but amounts for locations outside the axis varies.

At the Wise gridpoint, for example, model forecast snow amounts range from 1″ on the high-resolution NAM 3 KM Model to 5″ on the GFS Model ( the 12z run of the European Model was a compromise with 3″ predicted ).

If the precipitation band shifts southwest or northeast these amounts will change, and potentially in a big way.

Past climatology with warm fronts suggests that the area to the north and east of the Cumberland Mountains, focused upon the New River and Greenbrier valleys, will be most favored for a significant amount of wet snow.  That is the model consensus.

If movement of the actual low center ( the storm track ) shifts more south, then that would keep this area within snowfall for a longer period of time versus if the the storm track shifts north.  There remains some wiggle room.

Stay tuned for an update by Friday night.

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.

Mountain Area Forecast ( March 14-17 )

The Storm Prediction Center Has Issued A Marginal Risk For Possible Severe Thunderstorm Development On Saturday ( March 17 )

Former Alerts

ALERT For Strong SW-W Winds Developing Tonight At Upper Elevations…Then Mixing Downward Across The Area During Thursday

Strong upper elevation SW-W winds will develop tonight, with blowing-drifting snow possible in open areas & along high crest lines.  This could increase travel problems along State Route 619, State Route 706, Routes 238, 237, and State Route 160, to note a few, impacted by 6″ to 12″ of snowfall.

Strong SW-W winds will mix downward to middle elevation mountain ridges & exposed plateaus at some point between tonight and Thursday morning, then downward into lower terrain ( below 2000 feet ) during the day Thursday.

Wednesday Night Into Thursday Morning

Partly cloudy evening skies will give way to mostly cloudy conditions.  Becoming windy.  Blowing-drifting snow at the high elevations.  SW-W winds increasing to 10-20 mph, with higher gusts, on mountain ridges-exposed plateaus below 2700 feet.  WSW to W winds increasing to 20-30 mph, with higher gusts, on mountain ridges above 2700 feet.  Temps dropping into the 10s and 20s, then rising through the 20s at upper elevations overnight into morning ( nearly steady or rising above 30 degrees on exposed middle elevation mountain ridges & plateaus ).  Wind chills rising from the single digits below & above 0 degrees at highest elevations into the 10s toward morning.  Wind chills in the 10s and 20s along middle elevation ridges-exposed plateaus.

Thursday Afternoon

Partly to mostly cloudy ( mid-level clouds ).  Windy.  SW-W winds 10-25 mph, with higher gusts.  Temperatures varying from 30s to low 40s at upper elevations to the upper 40s to lower 50s ( milder in downslope locations with no snow ).

Thursday Night Into Friday Morning

Mostly cloudy.  Small chance of rain showers or a mix of snow showers possible at mid-upper elevations.  Winds shifting WNW-NW at 5 to 15 mph, with higher gusts.  Temps varying from 20s at upper elevations to the low-middle 30s ( milder in downslope locations, especially to the south and southwest of High Knob Massif-Tennessee Valley Divide ).

Friday Afternoon

Mostly sunny.  Some increase in high clouds.  Light NW-N winds, except breezy to gusty along high mountain ridges.  Temperatures varying from 30s to lower 40s at highest elevations over lingering snow cover to upper 40s to low  50s ( warmer south to southwest of the High Knob Massif and Tennessee Valley Divide ).  Wind chills in the 20s to lower 30s at upper elevations.

The potential for another major winter storm is being monitored for next week.  Stay tuned for later details.

25th Anniversary Of The March 1993 Superstorm

Reference the above link for a review of one of the greatest winter storms ever documented in this region ( scroll down to the section about the then 20th Anniversary of this Monster Storm ).

Recap Of Snow Squalls ( March 13-14 )

Reference my 031118 Forecast for information on the complete storm event including forecast details.

To understand how this was an easy forecast to predict days in advance, consider the following:

The temperature in downtown Norton is 60 to 70 degrees, while at the same time the temperature in downtown Wise is 0 degrees.  What would you think about that?

Now, invert that temperature difference into the vertical and you have the setting which developed  late on March 13 into morning hours of March 14.

When orographic lift is applied, it becomes chaos with widespread significant snowfall.  No places missed out in the upslope zone, even though amounts varied.

  In downslope locations, such an extreme vertical temp profile acted to overcome the typical inverse forcing with orographics ( often called downsloping ) and generated localized streaks of heavy snow.  Some to numerous places missed out.

The most intense snow squalls of the 2017-18 winter season created widespread, significant accumulations across the mountain area with Winter Storm Warning criteria easily exceeded within upslope locations of Wise County.

Snow squalls & local snowstreaks ( training squalls ) created whiteout conditions into morning hours of March 14, with new snowfall accumulations ( since sunset March 13 ) in the upslope zone varying from 2-3″ on the low end of the stick to 10″+ at upper elevations in the High Knob high country.

As little as 1″, by contrast, was reported in downslope sites such as in the Town of Big Stone Gap ( 1.4″ reported at the official recording site in the Tri-Cities ).

Snowfall & Snow Depth Reports
( March 13-14, 2018 )

Big Stone Gap
1.0″ ground depth
( Paxton Allgyer )

Clintwood 1 W NWS: 2.7″
2-3″ ground
( Wayne Browning )

Town of Wise
4″ ground depth
( Roddy Addington )

Pole Bridge Road – Wise
4″ ground depth
( Layton Gardner )

Ramsey
4″ ground depth
( Kyle Hill )

Pine Creek
5″ ground depth
( Kyle Hill )

Downtown Norton
6″ snow depth
( Jimmy Fawbush )

*City of Norton WP
6″-7″ ground depth
( Andrew Greear & Joe Carter )

*Parsons Gap – Wise
6.5″ ground depth
( Wally Smith )

*Depth included some old snow.

Joe & Darlene Fields measured a total of 10.0″ of new snow in the High Chaparral community of the High Knob Massif, with 8″ accumulating between 7 PM March 13 and 9:52 AM March 14, followed by an additional 2″ by the conclusion of this portion of the event ( 12.5″ total during March 12-14 ).

High Chaparral Community
10″ of total snow depth
March 12-14: 12.5″ Total
( Joe & Darlene Fields )

Snowstreaks developed into March 14 to produce prolonged periods of whiteout conditions along trajectories in which they formed.

Although several people reported hearing thunder, amid or immediately prior to onset of very heavy snow, including myself, the closest lightning strikes detected were very near the Virginia-Kentucky border in Pike County, Ky.; however, that does not mean that they did not occur on this side of the state line.

While the lightning detection system is very good and likely picks up most strikes, a few likely escape in such settings with CSI and a slantwise cloud over mountainous terrain.  There is no doubt that local snow was convective, with wind and intense snow so heavy that visibility was reduced to 100 meters or less amid climaxes.

Focus now shifts to an increasing pressure gradient as a frontal boundary approaches and stalls over the area, with wobbles back and forth to determine local temps as a rather significant NW-NE to SE-SW gradient develops across the boundary into this weekend.

Mountain Area Forecast ( March 11-14 )

ALERT For A Prolonged Period Of Wintry Conditions From Monday-Wednesday ( March 12-14 ).  The Worst Conditions Will Develop During Three Periods: 

Predawn to Mid-Morning of Monday ( March 12 )
*General 1″ to 4″ along-north of High Knob Massif

Updated: Monday At 4 PM
Monday Night-Tuesday Morning
NW Upslope Flow Snow Showers
( 1″ to 2″ with locally higher amounts )

Snow showers will redevelop in NW upslope flow during Monday Night into Tuesday Morning.  A general 1″ to 2″ of snow is expected along and west of the Cumberland Front, with locally higher amounts in the High Knob Massif. 

***NOTE: Whiteouts Are Coming***

Updated: Evening March 13
Late Tuesday PM-Wednesday AM
NW Upslope Flow Snow Squalls
( 3″ to 5″ with locally higher amounts )

Snow showers, intense snow squalls and possible snow-streaks are expected to develop in NW upslope flow during late Tuesday into Wednesday Morning.  Whiteout bursts of intense snow are expected to greatly reduce visibility and to generate widespread hazardous travel conditions, amid bitter air, along the upslope side of the mountains.

The main snow band is initially forecast by models to develop north of the Cumberland Mountains from the central portions of Kentucky into southern West Virginia, followed by a prolonged period of NW Upslope Flow with a Great Lake moisture connection as a strong mid-latitude cyclone intensifies over the western Atlantic Ocean.

Sunday Night Into Monday Morning

Rain developing.  Rain mixing with and changing to snow from top to bottom during the overnight-morning hours of Monday.  E-SE winds backing NE-N at 5-15 mph with higher gusts.  Turning colder with temperatures dropping into the low to mid 20s ( highest elevations ) to the low 30s ( Powell Valley and other low elevation sites ).  Wind chills falling into the 10s and 20s along mid-upper elevation mountain ridges.  Rime formation at highest elevations.

Monday Afternoon

Mostly cloudy.  Cold & windy.  A chance of snow showers & flurries.  NW winds 10-20 mph, with higher gusts.  Temps varying from 20s in upper elevations to the 30s at middle and lower elevations.  Wind chills in the 10s & 20s ( coldest in upper elevations ).

Monday Night Into Tuesday Morning

Snow showers & flurries redeveloping.  Localized snow squalls ( bursts of heavy snow ). Cold.  NW winds at 10-20 mph, with higher gusts.  Temperatures varying from middle 10s at the highest elevations to the mid-upper 20s.  Wind chills in the single digits & 10s, except dropping below zero in stronger gusts at highest elevations.

A setting favorable for intense snow squalls, with whiteout conditions, is currently shown by models to develop by late Tuesday into Tuesday Night.  This could be the worst period of this event given a combination of unseasonably cold air and bitter wind chills.

Tuesday Afternoon

Snow showers & flurries, with snow squalls becoming likely along with possible snowstreaks ( training squalls ).  WNW-NW winds 10 to 20 mph, with higher gusts.  Temperatures varying from 20s in upper elevations to the 30s at middle to lower elevations.  Wind chills in the 10s and 20s ( coldest in upper elevations ).

Tuesday Night Into Wednesday Morning

Snow showers & squalls ( possible snowstreaks ).  Cold.  Winds WNW-NW at 10-20 mph with higher gusts.  Temps dropping into 10s to around 20 degrees, except single digits to around 10 degrees at highest elevations.  Wind chills in the single digits and 10s, except below zero at highest elevations.  Rime formation at high elevations.

25th Anniversary Of The March 1993 Superstorm

Reference the above link for a review of one of the greatest winter storms ever documented in this region ( scroll down to the section about the then 20th Anniversary of this Monster Storm ).

Weather Discussion ( Models Struggle )

Tuesday Afternoon Update

While only light snow showers & flurries have occurred so far during Tuesday, DO NOT THINK that is going to remain the case.

While worst conditions will develop between midnight and sunrise Wednesday, impact snow squalls will start to develop during the sunset-midnight period ( if not locally before ).  I expect intense squalls with a very potent upper air setting that will combine with low-level orographics.  Be Prepared!

Monday Evening Update

I updated to introduce snow squalls earlier than in my initial forecast, with 0.5″ of new snow accumulating within only around 10 minutes in Clintwood prior to midnight.  I have also added the possibility of snowstreak formation during Tuesday afternoon and Tuesday Night with a very unstable atmosphere developing on forecast soundings.

*Local thundersnow or CSI slantwise convection will be possible.

Monday Afternoon Update

A cold, damp atmosphere is lingering in wake of the first round of snowfall with cloud bases trying to lift and break as of late afternoon ( a battle between NW usplope flow and a temporary surge of drier air ).

UVA-Wise graduate Layton Gardner just measured 2″ of mean snow depth on the ground at his home in Wise.

A total of 1.4″ of snow fell in Clintwood ( 1″ on the ground ) versus a general 2-4″ of ground depth from northern slopes at the City of Norton Water Plant ( 2″ ) to upper elevations in the High Knob Massif ( High Chaparral to Eagle Knob ).

The focus now turns to unseasonably cold air and the re-development of flurries, snow showers, and eventually squalls in a Great Lake connected NW upslope flow.

While low density snow will drop a new 1″ or 2″ on the upslope side of the Cumberland Front by Tuesday AM, the worst period upcoming will likely develop by late Tuesday into Wednesday when a setting favorable for intense snow squalls and possible snowstreaks ( which are training squalls ) will develop.

Both Lake Superior & Lake Michigan, from which streamline flow will originate, are wide open for business, so it will be GAME ON as this interacts with the high terrain along and just west of the Cumberland-Allegheny Front.

Previous Discussion

Forecast models continue to struggle with a system that has been seen to be problematic now for days.  The development of a heavy, but narrow band of snow is again being shown, surrounded by lighter snowfall, with exact placement of  this band and timing of a change from rain to snow being the core problems ( giving forecaster’s heartburn and a decreasing amount of follicular hair!!! ).

Differences in models are displayed in their snowfall forecasts for the next 24-hours, with little to none being shown by the operational GFS ( above ) to heavy snow on  the high resolution NAM ( below ) for upslope locations within far southwestern Virginia.

The European Model and its 51-Member Ensemble MEAN, which I am not allowed to show, is currently a compromise between these solutions with a forecast of 3″ in Wise and a general 1-3″ across the area during the next 24-hours.

But the European struggles to resolve local terrain features, such that if a easterly flow continues into early Monday no snow will be able to stick in Powell Valley vs. heavy snow at elevations over 3000 feet just above within the High Knob Massif ( especially if a rain-snow melting zone develops along Powell Valley as documented in past events* ).

*That would be a TIM Circulation ( a Thermally Indirect Mesoscale circulation that I have documented in research during past decades ).  Uncertainty associated with how long such a flow will be sustained is the main reason I am not highlighting this currently, but it could be a notable player in this system and I may update later if it forms.

Ironically, the easiest part of this forecast is currently out in the 48-72 Hour range when moderate-strong NW upslope flow will combine with bitterly cold air aloft to generate a setting favorable for whiteout snow squalls…especially in locations along & west of the Cumberland-Allegheny Front.

Atmospheric parameters currently being forecast are prime for intense snow squalls, with whiteout conditions and the potential for significant accumulations of low density snow such that this must be closely monitored and updated as cyclogenesis occurs over the western Atlantic Ocean.

Mountain Area Forecast ( March 8-10 )

An Alert For Local Snow Accumulation Continues Into Saturday Morning; However, Amounts Will Likely Be Much Less Than Earlier Indicated.  Many Places May Have Little To No Accumulation.

A northward shift in the main snow band has developed on evening model runs, with a narrow area of heaviest impact stretching from portions of central Kentucky into southern sections of West Virginia ( along a LEX to BKW line ).

Locally, a dusting up to 2″ is now forecast with locally more at upper elevations within the high country of the High Knob Massif only if a predawn-morning corridor of moisture can develop as suggested by some short-range guidance ( otherwise, even at the highest elevations amounts will be 2″ or LESS ).

Updated Snowfall Forecast
Friday Night-Saturday Morning

A dusting up to 2″ along and north of a Harlan, Ky., to Marion, Va., line with little to none to the south and a narrow band of heavy snow to the north across parts of eastern Kentucky into western West Virginia.

Target Snowfall of 1.0″ in Norton-Wise ( +/-) 1″ error potential, suggesting a dusting to 2″ will be possible with locally higher snow amounts within the High Knob Massif and only at highest portions of the Tennessee Valley Divide into Saturday ( March 10 ).

*A transition to rain may first occur north of the High Knob Massif and Tennessee Valley Divide where SSW-WSW winds downslope into northern Wise, Dickenson, and Buchanan counties, with the longest period of snow likely at upper elevations in the High Knob Massif and along portions of the Tennessee Valley Divide where SSW-WSW winds upslope ( the bulk of this initial event will be snow in the High Knob high country ).

European Model and GFS Model Ensemble Means suggest another period with possible significant snow will occur Sunday into Monday ( March 11-12 ).  Stay tuned.

Thursday Night Into Friday Morning

Mostly cloudy with snow showers, flurries, and local squalls ending into morning.  W- NW winds 5-15 mph, with higher gusts, on mountain ridges and plateaus below 2700 feet.  WNW-NW winds 10-20 mph with higher gusts on mountain ridges above 2700 feet.  Temperatures widespread in the 10s ( upper elevations ) and 20s ( low-middle elevations ).  Wind chill factors in the 10s to around 20 degrees, except in single digits above and below zero on highest peaks.

Friday Morning Through The Afternoon

Thickening and lowering clouds ( from mid-high clouds in mid-day to low clouds by end of day ).  Virga developing by late.  WSW winds 5 to 15 mph, with higher gusts.  Temps varying from 20s at upper elevations to the middle 30s to lower 40s.  Wind chills mainly in the 10s & 20s along mid-upper elevation mountain ridges & exposed plateaus, coldest at highest elevations.

Friday Night Into Saturday Morning

Light snow & flurries.  A period of heavier snow possible by the predawn-morning hours.  Winds SW-WSW at 10 to 20 mph, with higher gusts, on upper elevation mountain ridges.  Temps in the 20s to lower 30s, tending to rise toward morning.  Wind chills in the 10s and 20s along higher mountain ridges.

Weather Discussion ( Active Pattern )

Friday Night Update

Although a dusting of new snow has occurred in upper elevations of the High Knob Massif Friday evening, the latest forecast model trends are for a much more narrow, mesoscale band of heavy snow to develop farther north than indicated by many previous runs.

*The 7:00 AM Friday run of the high-resolution WRF model was showing enough moisture for 5-6″ of snow at upper elevations of the High Knob Massif, versus the 7:00 PM run which predicts only around 0.5″ or less.  Reality may rest in between, but time will tell.

Even better than Doppler, at this point, the low-level water vapor imagery from GOES-16 shows the mesoscale banding nature across Kentucky that is creating havoc with models forecasting this event ( scroll to the USA for a view ).

LIVE Streamline View At 250 MB Level

A fast and nearly zonal flow across the region is making it more difficult for models to resolve the impacts of a wave embedded within the flow ( shortwave seen at 700-500 MB ) near the Mississippi River as of 11:00 PM Friday.

A batch of moisture over far southeastern Missouri and western Kentucky looks to ultimately be the area to watch into the predawn to mid-morning of Saturday for a possible period of moderate-heavy snow that may form southward of the main mesoscale ( narrow ) band…especially at the middle-upper elevations ( some short-range guidance is forecasting this to also miss the area ).

It is always frustrating when model guidance makes an abrupt change during the onset of an event, but it happens and the ultimate result will not be known until another 12-hours have passed.  This illustrates that Mother Nature is in control and that settings like this will likely continue to be problematic to even the best models and forecasters.

Previous Discussion

A combination of bitterly cold air aloft and terrain generated a classic snow squall day in the mountains during Thursday.

*UVA-Wise graduate student Layton Gardner measured 1″ on the ground during the morning at his home on the Wise Plateau.

Vertical cloud development in wake of overnight squalls was a signal of more to come during the day, with locally intense, hit or miss snow squalls.

Melting and sublimation in between squalls = a very tough day to obtain an accurate measurement unless you were a dedicated and/or veteran snow observer.

Clintwood 1 W NWS
Snowfall Observations
( Elevation 1560 feet )

7:00 AM
0.2″ / Trace on ground

10:30 AM
1.1″ new snow / 1″ on ground

11:30 AM
0.6″ new snow / 1″ ground

12:15 PM
1.0″ new snow / 2″ ground

Total: 2.9″ ( up to 12:15 PM )

Melting and sublimation in between the squalls held the ground accumulation well under the total snowfall.

The more intense snow squalls were convective and typically signaled by darkening skies and a gush of wind, with fine graupel snow that gave way to larger, often huge, flakes unless wind and downdraft motion was so strong as to break up the big flakes into fragments.  Visibility typically dropped to well under 0.25 mile.

Conditions were similar in Wise with huge snowflakes, like in Clintwood, at times, and melting in between with sinking air around these intense squalls ( air converges and rises in the squall and sinks around its periphery to generate cloud breaks ).  This pattern, and a clear indication of bitterly cold air aloft, was documented well by GOES-16 visible imagery.

The array of cloud “blobs” visible on this image are the many snow squalls and heavier snow showers that were developing beneath very cold air aloft.  Terrain helped to focus the most intense action along and west of the Cumberland-Allegheny Front.

Snow accumulations with warm air transport systems can be problematic, such that positioning of the main band and amounts will be tricky.  Evaporative cooling + upslope flow into the High Knob Massif and Tennessee Valley Divide will favor some of the heavier amounts.

An area of enhancement on the windward side of major terrain features, and lesser amounts on the down-wind side, is trying to be picked up by models to fit observed climatology of such events.

At least, through Friday morning, models are coming toward my forecast and not away from it so time will tell.  Certainly some slick conditions are looking likely regardless of exact snowfall amounts into Saturday.

Mountain Area Forecast ( March 5-8 )

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.

Reference February 2018 – The Wettest On Record In Virginia for a recap of this past month of record setting precipitation.

Weather Discussion ( Wintry Pattern )

Evening Update On March 7

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.

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 ).

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 ).

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.

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 ).

A Cody Blankenbecler image ( below ) shows what it looks like inside the orographic cloud ( like a dark, dense fog ).

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 ).

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.

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.

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.