Mountain Area Forecast ( Jan 29-31 )

ALERT For The Development Of Accumulating Snow And Hazardous Travel Conditions During Sunday Into Monday Morning ( January 29-30 )

Monday AM Update At 2:45 AM – Another area of heavy snow is beginning to move into Wise County from the west and will overspread the Norton-Wise and U.S. 23 corridor through 3:00 to 3:30 AM.  Blowing snow will add to the reduction in visibility which is expected to be near zero at times.  Another band of snow will be moving into portions of northern Dickenson and Buchanan counties.

*A persistent streak of snow has dropped significant amounts from Black Mountain into portions of the High Knob Massif since Midnight.  Expect difficult travel conditions in upper elevations, with travel not recommended.  Drifting snow is occurring.

A region of very cold air aloft will trigger flurries, snow showers and bursts of heavy snow in squalls and streaks of heavy snowfall during Sunday into Monday morning.  While the greatest amounts of snow are generally expected along the windward ( SW to NW )  sides of the Cumberland and Blue Ridge mountain ranges, locally heavy snow may also occur in portions of the Clinch, Powell, and Holston valleys.  The worst driving conditions are anticipated from late Sunday afternoon into early Monday with widespread hazardous travel developing along the usplope side of the mountains ( where SW to NW air flow rises ).

Expect rapidly changing weather and low visibility, with near whiteout conditions, in the more intense squalls and streaks of snow during Sunday PM into Sunday Night.  Caution is advised.

**An ALERT For ROARING SW Winds Will Likely Be Needed For Monday Night Into Tuesday.

 

Overnight Into Sunday Morning

Periods of flurries & snow showers.  Little accumulation.  Winds SW-WNW at 5-15 mph, with higher gusts.  Temps dropping into the 20s to lower 30s.  Wind chills in the 10s and 20s ( coldest on upper elevation mountain ridges ).

The best coverage of snow showers and heavier squalls is expected to generally be along and southwest of the High Knob Massif and Tennessee Valley Divide during much of Sunday, from the Wise & Sandy Ridge plateaus southwest along the Virginia-Kentucky  stateline on SSW-WSW flow.  Coverage of activity is expected to increase as instability increases into mid-day to early afternoon.

Downsloping and somewhat milder temps is expected to produce less snow accumulation toward Pound, Clintwood, and in adjacent communities across northern Wise and much of Dickenson County prior to a late afternoon wind shift.   

Sunday Afternoon

Snow showers, flurries and snow squalls-streaks of heavy snow.  Heaviest snow amounts along and southwest of the Tennessee Valley Divide and High Knob Massif.  Winds SSW-WSW at 5-15 mph, with higher gusts, shifting W-WNW late.  Temperatures in the 20s to low-mid 30s.  Wind chills in the 10s and 20s.

A wind shift to W-WNW by late Sunday afternoon into Sunday evening is expected to change the focus for heavier snowfall amounts toward locations along and west to northwest of the  High Knob Massif & Tennessee Valley Divide on W-WNW flow.

Due to very cold air aloft, any location will be at risk for a burst of heavy snow; although, best coverage is expected where air flow is forced to rise on SW to NW trajectories. 

Sunday Night Into Monday Morning

Snow showers, flurries, and snow squalls-streaks of heavy snow taping to flurries and localized snow showers toward morning.  Winds W to NW at 10-20 mph, with higher gusts.  Temperatures varying from around 10 degrees at highest elevations to the upper 10s to lower 20s.  Wind chills in the single digits and 10s, except below zero in upper elevations.

Snowfall Forecast – Sunday Into Monday Morning

A general 2″ to 6″ is expected, with a target snowfall of 4″ in the Norton-Wise area ( +/- 2″ error potential ).  Locally higher amounts will be possible at upper elevations in the High Knob Massif.  Snow depths are expected to be less than total snowfall at lower-middle elevations, where some melting will occur during Sunday.  Snow to water ratios are expected to be greater than 10:1 ( snow density low ), especially by later Sunday into Sunday Night due to bitterly cold air aloft and a relatively deep dendritic crystal growth zone within the vertical ( i.e., moisture intersecting bitter cold air ). 

Monday Afternoon

Partly cloudy.  Cold.  WNW-WSW winds 5-10 mph, with higher gusts.  Temperatures varying from the mid-upper 10s to the mid-upper 20s to lower 30s ( coldest in upper elevations ).

Monday Night Into Tuesday Morning

Variable clouds.  Becoming windy, especially at middle to upper elevations.  Temps in the 10s and 20s, then rising into the overnight-morning ( especially on mid-upper elevation mountain ridges ).  SSW-WSW winds increasing to 15-25+ mph, with higher gusts.  Wind chill values in the single digits and 10s, then rising values into morning.

 

Weather Discussion ( Bursts Of Snow )

Widespread snow will be impacting the mountain area on Sunday into early hours of Monday, with worst conditions developing by later Sunday into Sunday Night.

Abundant moisture and rising air during Sunday PM into Sunday Night will combine with cold air aloft to produce widespread snow and bursts of heavy snow.

There is no doubt that snow will be widespread, but amounts will vary significantly due to a combination of factors between the surface and middle troposphere ( i.e., 700-500 MB layer ).

While I expect the worst conditions to develop around and after a wind shift occurs between 1:00 PM and 7:00 PM on Sunday, there will likely be notable differences in weather conditions prior to that time with SSW-WSW flow favoring the heavier snowfall and accumulations to occur in locales where this air flow rises ( from the Sandy Ridge and Wise plateaus southwest to Norton, Powell Valley-Big Stone Gap into portions of Lee County ) versus where it sinks ( from Pound-Clintwood toward Haysi and Grundy ).

*This will be partly due to the cooling that occurs with rising air that will help keep surface temperatures lower within the lifting zone versus where this air flow sinks.  The strongest cooling and best accumulations, of course, being most favored across upper elevations in the High Knob Massif and the Black mountains.

Forecast soundings show a deep saturated layer with a steep temperature decline late Sunday into Sunday Night to support development of widespread snow, abundant bursts of snow and hazardous driving conditions.  So regardless of what happens prior to sunset on Sunday, I expect upslope locations ( with respect to W-WNW air flow ) to have the worst conditions form during this time.

*This is a classic sounding profile that past climatology shows tends to be very productive.  The main missing ingredient to keep this going and enhance it further is a lack of deep connection to the Great Lakes ( a notable missing ingredient so far during the 2016-17 Winter Season across the southern Appalachians…if this was present I would be going significantly higher on my forecast snowfall numbers ).

The Bottom Line

Widespread snow is expected Sunday into Monday AM, with an initial focus of most numerous snow showers, squalls and snowstreaks being biased toward locales where SSW-WSW air flow rises ( e.g., Wise southwest toward Big Stone Gap ) prior to a wind shift timed to occur by late afternoon Sunday.

A wind shift toward W-WNW will tend to shift the focus for most widespread snow showers, squalls and snowstreaks to locations along and west to northwest of the High Knob Massif and Tennessee Valley Divide during Sunday Night into early hours of Monday.

*Max accumulations during this event occurring where these two zones overlap, ideally, across the High Knob Massif and along the Tennessee Valley Divide.  Cold air aloft ( as noted below ) could locally skew this and allow for significant amounts in places outside of this orographic overlap zone via bursts of snow.

Due to very cold air aloft, and relatively deep moisture intersecting a zone prime for dendritic crystal growth, I expect bursts of intense snow to generate whiteout type of conditions ( i.e., low visibility ) at times.  This puts any location at risk for a burst or bursts of snow.

The worst travel conditions are expected to develop on a widespread basis by late Sunday into Sunday night.

I expect widespread school closings and delays for counties within the mountains on Monday.