010417 Forecast

Mountain Area Forecast ( January 4-7 )

ALERT For Accumulating Snow & Hazardous Travel Developing Thursday Afternoon Into Friday Morning

Low dewpoint air moving into the Cumbeland Mountains will allow temperatures to drop significantly into Thursday Morning, followed by increasing clouds that keep temperatures cold during Thursday to set the stage for development of a moderate impact snowfall event by late Thursday into Friday.
Widespread hazardous travel conditions are expected to develop during Thursday PM-Evening into Friday Morning.  Bitter temps and wind chills will add to these hazardous conditions.

An ALERT For Accumulating Snow May Be Needed For Late Friday Into Saturday Morning As A Second Wave Impacts The Mountain Region

Overnight Into Thursday Morning

Mostly clear into the overnight then increasing high clouds.  Cold.  W-NW winds 5-15 mph, with higher gusts, becoming light.  Temps in the 10s to low-mid 20s, varying from 10-15 degrees in high valleys of the High Knob Massif to low-mid 20s along exposed middle elevation ridges.

Mid-Morning Thru Thursday Afternoon

Cloudy.  Cold.  Light winds.  Virga developing aloft, then flurries and light snow reaching the surface.  Temperatures generally varying from the 20s to the lower 30s.

Thursday Night Into Friday Morning

Snow.  Turning bitter.  Winds WNW-NNW at 5-15 mph, with higher gusts.  Temperatures dropping into 10s to around 20 degrees ( as cold as 10 degrees at highest elevations ).  Wind chills in the single digits and 10s, except below zero in gusts along upper elevation mountain ridges.  Rime formation in upper elevations.

Friday Afternoon

Morning snow tapering to flurries and snow showers.  Bitter cold.  Winds NW to N at 5-10 mph.  Temps  varying from lower-mid 10s in upper elevations to lower-middle 20s.  Wind chill factors in single digits & 10s ( coldest at highest elevations ).

Snowfall Forecast: Late Thursday to Late Friday

A general 1″ to 4″ of snowfall is expected in counties along the Virginia-Kentucky border, with locally higher amounts possible at upper elevations of the High Knob Massif ( least snowfall amounts are expected across central-western Lee County and portions of the Clinch & Holston river valleys ).

Target Snowfall 3″ In Norton-Wise ( +/- ) 1″ Error Potential.  This suggests a possible range from 2″ to 4″ in Norton-Wise during this period.  Snow Density will be lower than 10:1 in locations along & north to northwest of the High Knob Massif and Tennessee Valley Divide to generate more “fluff factor” than in locations farther to the southeast ( i.e., the snow to water ratio will be locally higher ).

Friday Night Into Saturday Morning

Periods of snow & snow showers.  Heavy at times.  Bitterly cold.  NNW-N winds 5-15 mph, with higher gusts on middle-upper elevation mountain ridges.  Temperatures varying from 0 to 12 degrees.  Wind chills from 5 above to -10 below, except -10 to -20 degrees below zero upper elevation ridges.

A second storm system lifting northeast out of the Gulf of Mexico is now forecast to impact the mountains late Friday into Saturday morning, with an update to the forecast noted above. 
Sunday & Monday morning’s ( January 8-9 ) will both feature bitterly cold temperatures, especially in mountain valleys, with single digits and sub-zero temperatures being possible.  Please stay tuned for later updates.


Weather Discussion ( Harsh Period )

Thursday Afternoon Update

An initial wave of snow dropped 0.5″ to 1″ of accumulation across portions of northern Wise and Dickenson counties into early afternoon Thursday, before waning.

I officially measured 0.5″ of snow in Clintwood, with heavier snow to the north and northeast toward Pine Mountain and Breaks Park.
High Knob Massif Webcam – University Of Virginia’s College At Wise

Although flurries and light snow showers have occurred throughout Wise County, the lower atmosphere south of Pound has not yet been able to saturate with abundant amounts of low-level dry air.

JKL Doppler Radar At 4:22 PM on Thursday – January 5, 2017

A developing area near Middlesboro on Doppler radar is expected to be the beginning of saturation and sticking snow as it lifts northeast across Lee-Wise counties and northern portions of Scott County into this evening.

This system is coming in waves instead of one consolidated area of energy ( at least at this time ), with an initial wave impacting sites to the north while the current developing area of snow denotes a wave that will impact locations farther to the south ( e.g., Wise County which mostly missed sticking early afternoon snow ).
Conditions for snowfall will be improving into Thursday evening as a low-level wind shift to the NW-N increases upslope into the High Knob Massif area and temperatures begin to turn colder.
NAM 4 KM Model Total Snowfall Forecast

Meanwhile, the past several runs of the NAM Model group have become aggressive in spreading the heaviest snow across the Mountain Empire late Friday into Saturday.

The Morristown NWS Forecast Office has issued a Winter Storm Watch for later Friday into Saturday.  I will wait to this initial period passes tonight before updating my snow forecast for this second event.  There remains substantial model disagreement with respect to how much moisture reaches the area.  Stay tuned for later updates.


Previous Discussion

A harsh period of winter conditions will dominate the mountain landscape during upcoming days.  While no big winter storm is expected, the combination of bitter cold air and some snow will create the harsh conditions, especially in a season where this type of weather has been limited.

High Knob Massif Webcam – University Of Virginia’s College At Wise
Rain showers changed to snow showers & flurries into early Wednesday with a little accumulation at high elevations in the High Knob Massif.  The most important aspect; however, was clearing skies with advection of much drier, lower dewpoint air into the mountains.  This will allow for cold conditions into the daylight hours of Thursday, as clouds increase, and set the stage for a Moderate Impact winter event late Thursday into Friday.
European Model 850 MB Temps & Sea Level Pressure At 7 AM Wednesday

A huge mass of bitterly cold air will continue to move south and southeast into the mountains during the next few days. 

NAM 4 KM Model Total Snowfall Forecast To 7:00 AM Friday – January 6, 2017

The NAM Model group has nearly all the snow falling with the first disturbance across the Cumberland Mountains, as the second and much bigger wave spreads snow across parts of the Deep South into the Carolina’s and the TN-NC border this weekend.  The latest European Model run ( 00z ) has cut back amounts across the board, except for the Deep South & Carolina’s ( a bulls-eye of 12″-15″ being centered mainly on the zone that got devastated by Hurricane Matthew flood waters in central-eastern North Carolina on the ECMWF ).

NAM 12 KM Model Total Snowfall Forecast To 7 AM Sunday – January 8, 2016

I always have some Error Potential factored into my snow forecast’s; however, if this reduction trend continues then totals may have to be cut back ( as it stands now, the NAM data would allow it to verify while the new European Run would make it a push to reach the lower end of the range ).

This remains true since models are forecasting at 10:1 density, and with very cold air in the vertical column + a period with moisture intersecting the prime dendritic crystal growth temperature zone the actual snow density will be significantly lower ( snow to water ratios will be higher than 10:1 ).
NAM 4 KM Model MIN Temperature Forecast At 7 AM Saturday – January 7, 2017

Regardless of snowfall amounts, conditions are going to be bitter Friday through this weekend with 0 to 10 degrees by Saturday Morning and the potential for even colder MINS, especially in mountain valleys, on Sunday & Monday AM’s.

Update: 1 AM Thursday NAM Model Run

NAM 4 KM Model Total Snowfall Forecast To 1:00 AM Friday – January 6, 2017

In opposition to the last European Model run, the overnight NAM Model group has come in wetter and also now brings accumulating snow into the mountain area from the next wave tracking across the Deep South.

NAM 4 KM Model Total Snowfall Forecast To 1:00 PM Saturday – January 7, 2016

Clearly, the models are struggling to handle these waves embedded within fast flow aloft tracking across the USA against a huge arctic air mass to the north.

Stay tuned for more updates.