020218 Forecast

Mountain Area Forecast ( Feb 2-4 )

ALERT For Hazardous Conditions Developing Overnight Into The Predawn-Morning Hours Of Sunday ( February 4 )

ALERT For Strong SSE-SSW Winds Developing Along Mid-Upper Elevation Mountain Ridges Into Sunday

Another fast moving weather system will begin impacting the mountain region Saturday Night into Sunday Morning, with development of strong winds at mid-upper elevations and lowering cloud bases that will give way initially to snow.
Snow may become heavy before a transition to sleet and freezing rain and rain occurs during Sunday.  A change back to snow, with additional accumulation, is expected Sunday Night into Monday morning as air once again turns bitterly cold.  Numerous school schedule changes are expected to become necessary for Monday.

Friday Night Into Saturday Morning

Partly-mostly clear through the evening, then increasing high clouds overnight into morning.  Bitterly cold.  Light winds, becoming WSW-W at 5-10 mph, with higher gusts, along high mountain ridges.  Temperatures in the single digits to low 10s, except below zero in colder mountain valleys at upper elevations of the High Knob Massif to Burkes Garden corridor.  Sub-zero wind chills on high mountain ridges.  Temps tending to rise along upper elevation mountain ridges overnight.

Saturday Afternoon

Mostly cloudy ( mid-high clouds ).  SSE-SSW winds 5-10 mph, with higher gusts, below 2700 feet.  Winds SSW-SW at 5-15 mph, with higher gusts, above 2700 feet.  Temps varying from the 20s to near 30 degrees in upper elevations to the mid-upper 30s.  Wind chills in the 10s & 20s along higher mountain ridges.

Snowfall Forecast – Two Different Periods

 I ). Predawn-Morning Hours Of Sunday

A general 1″-2″ with locally higher amounts possible

This is the most difficult period to forecast since it has HUGE BUST potential, let that be stated CLEARLY with either little to no snow accumulation if warm air advection is fast enough to overcome evaporative cooling and other factors, or with significantly more snow should column cooling trend toward an isothermal vertical profile during the period of heaviest precipitation.  I have gone in between these two scenarios, with 1″ to 2″ prior to a transition.

The High Knob Massif and Norton-Wise to Sandy Ridge area is of most concern with a potential to over-achieve, while lower elevations in Powell Valley and farther north into portions of northern Wise-Dickenson-Buchanan counties have the highest potential to under-achieve ( with little to no snow ), especially if winds can penetrate through a low-level inversion which will be trying to develop above the cold, still snow covered ( in many places ) ground. 

II ). Sunday Night Into Monday Morning

A general 1″-2″ along the Upslope Side of the mountains with respect to NW flow ( i.e., along and west-northwest of the Cumberland-Allegheny Front ).

This is the easy period of the forecast with upslope snow showers developing as bitter cold air pours back into the mountains during Sunday Night into Monday.  This will generate low density, fluffy snow with high snow to water ratios.

Saturday Night Into Sunday Morning

Lowering cloud bases.  Becoming windy.  Snow developing overnight into the morning, becoming mixed with sleet or changing to rain at lower elevations.  Snow may be heavy.  SSE-S winds 10-20 mph, with higher gusts, below 2700 feet.  S-SW winds 20 to 30+ mph, with higher gusts, on mountain ridges above 2700 ft.  Temperatures in the 20s to lower 30s.  Wind chills in the 10s and 20s, except single digits possible at highest elevations.

Sunday Afternoon

Any snow or mixed precipitation changing to rain.  Low clouds and areas of widespread dense fog.  Nasty.  Winds SSE-SW and shifting to W by late at 5-15 mph with higher gusts.  Temperatures mainly in the 30s ( rising into the lower 40s in downslope locations if winds are able to penetrate a low-level inversion.  Wind chill factors in the 20s to lower 30s.

Sunday Night Into Monday Morning

Turning bitter cold with rain changing to snow showers.  Wind shifting NW at 10-20 mph, with higher gusts.  Temps dropping into the 10s to around 20 degrees at low-middle elevations and into single digits at the highest elevations.  Dense fog ( clouds ) with riming at upper elevations around and above 3300 feet.  Wind chills plunging into the single digits above and below zero, except to colder than -10 F below zero at highest elevations.


February 1-2 Winter Storm Recap

High Knob Massif Webcam – University Of Virginia’s College At Wise ( Heavy Snow )

Although a SW upslope flow snow did not develop, a rain-snow mix occurred Thursday afternoon at the summit level of the High Knob Massif prior to a change to heavy snowfall between 6 to 7 PM.  A while later heavy snow also developed at UVA-Wise ( above ).

*Reference later notes on why a SW upslope flow snow did not realize its potential, and it was predicted to only be a potential.
High Knob Massif Webcam – University Of Virginia’s College At Wise

This webcam at UVA-Wise is named the High Knob Massif cam since it looks at part of the lofty crest line which rises just south of Wise; however, at this time the massif was still standing amid clouds producing rime and snow.

Ground Depths
(Snowfall Totals )

Clintwood: 2″ to 3″
( 2.3″ at Clintwood 1 W )

Norton-Wise: 2″ to 4″+
( 3.6″ measured by Layton Gardner )

High Chaparral: 3″ to 5″+
( 4.5″ measured by Joe & Darlene Fields )

*High Knob-Eagle Knob: 3″ to 12″+
( 6.0″ of snowfall )

*Note the large snow depth variations at high elevations in the High Knob Massif, with wind driven horizontal snowfall.  The actual fall could have been higher than the total estimated.
Eagle Knob of High Knob Massif At 7:44 AM Friday ( 8 degrees – Gusty N winds )

Can you detect a trend in this data, certainly, a notable increase in snow amounts with increasing elevation.

While that might often be the case, in this event it was especially true due to faster changes to snow at middle to upper elevations versus lower elevations ( below 2K feet ).

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

A gorgeous conclusion to a bitterly cold winter day featured orographic standing wave clouds illuminated by the setting sun, with flakes of snow still falling in flurry form.

Eagle Knob of High Knob Massif At 5:50 PM ( Feb 2 ) – Elevation 4196 Feet

A beautiful array of mountain wave and instability clouds were captured by the daily MODIS pass of the Terra satellite.

MODIS Terra Satellite Image on February 2, 2018

My snowfall forecast verified because the system was intense, with good orographic forcing despite its rapid movement.

NAM Model Forecast Sounding For February 1 at 4:00 PM

A couple factors prevented the SW upslope from producing snow.  A slow but steady increase in moisture allowed the atmosphere to saturate from the top downward in advance of precipitation to help minimize evaporative cooling + the advection or transport of warm air around and just above 850 MB was just a little stronger than initially forecast; therefore, I only predicted this as being a potential.

Actual Initialized Atmospheric Sounding At 1:00 PM on February 1, 2018

It was a very close setting, with snow mixed with rain at the summit level of the High Knob Massif Thursday afternoon prior to an early evening change.  Temps at high elevations fell quickly to freezing given they did not have far to drop.

Past climatology shows there is a somewhat higher probability of having SW upslope flow snow events during La Nina winters.