Mountain Area Forecast ( Dec 31-Jan 3 )

ALERT For Bitterly Cold Air To Continue Through New Year’s Day Into Tuesday

Air temperatures will remain below 20 degrees at middle-lower elevations, and below 10 degrees at upper elevations, along and north of the High Knob Massif-Tennessee Valley Divide, into Tuesday.  Wind chills will make conditions feel much colder at times, especially at middle-upper elevations.

While New Year’s morning ( Monday ) will tend to be coldest at highest elevations, on peaks, both Tuesday & Wednesday mornings will tend to be coldest in mountain valleys.

Extreme Caution Is Advised To Protect Against Frostbite & Hypothermia For All Warm-Blooded Creatures Which Have To Balance A Heat Budget

New Year Eve Into New Year Morning

Partly to mostly cloudy.  A chance of flurries and snow showers overnight into morning.  Bitter.  NNW-NNE winds 5-10 mph with higher gusts along middle-upper elevation mountain ridges-exposed plateaus.  Temperatures varying from -5 below zero to 8 degrees.  Wind chills 5 above to -10 below zero at elevations below 2700 feet, with chill factors of -5 to -15 below zero at elevations above 2700 feet ( as cold as -20 to -25 degrees below zero on highest peaks ).  Rime formation possible again at highest elevations.

Afternoon Of New Year’s Day

Mostly cloudy with flurries and snow showers continuing.  Bitter.  NW winds 5 to 10 mph with higher gusts.  Temps varying from single digits in upper elevations to 10s at middle-lower elevations in locations along-north of the High Knob Massif and Tennessee Valley Divide ( a little “warmer” south into river valleys of the Clinch, Powell, Holston ).  Wind chills in single digits above & below zero, except -10+ below zero in gusts highest elevations.

Monday Night Into Tuesday Morning

Becoming mostly clear.  Chance of evening flurries.  Bitter.  NW-NNW winds 5-10 mph, with higher gusts, mid-upper elevation mountain ridges.  Light valley winds.  Temps varying from  5 above zero -5 below zero, except locally as cold as -10 F below in upper elevation mountain valleys.  Wind chills between 0 degrees and -25 below zero along exposed mountain ridges ( coldest at upper elevations ).

Tuesday Afternoon

Mostly sunny.  Bitter.  Light NW winds.  Temperatures varying from the 10s to lower 20s ( mid 20s possible in exposed middle elevation locations with a low-level inversion being possible to keep some valleys colder ).

Tuesday Night Into Wednesday Morning

Clear through the evening.  Increasing high clouds overnight into morning.  Light winds becoming SW along mid-upper elevation mountain ridges.  Rapid evening temp drop in mountain valleys.  Temperatures varying from 10s along mountain ridges to single digits in valleys, except below zero in colder valleys at upper elevations.

The chance for more significant snowfall is being monitored with development of NW upslope flow behind major cyclogenesis in the western Atlantic by January 4-5 in combination with a reinforcing surge of bitterly cold air.  Stay tuned for updates.

 

Weather Discussion ( Bitter Cold )

New Year Day Update

My update is to continue mostly cloudy skies with flurries and snow showers this afternoon as low-level moisture has been greater than models resolved amid this bitter air.

Flurries and snow showers redeveloped in the overnight and morning hours of New Year’s Day, as I had forecast, and are continuing at upper elevations in the lifting zone of the High Knob Massif and across upslope locales this afternoon.

The air temperature was just 2 degrees, with well below zero wind chills, on Eagle Knob at the time of the above view when a peep of sunshine helped to illuminate the flakes.

Temperatures had warmed to a relatively “balmy”, by comparison, 15 degrees in Clintwood at 3:30 PM, with readings having climbed to about 10 degrees at Nora 4 SSE ( below ).

An interesting local feature that I picked out was a plume generated by cold air flowing down South Holston Lake on NNE flow during the morning.

This NASA pre-sunrise image, which is essentially infrared, was able to detect ( as it often does ) the warmer surfaces of the largest TVA Lakes in northeastern Tennessee which show up as a darker hue amid more light colors.  Upslope clouds, the edge of which I denoted by a red line, could also be seen distinctly.

In this case the air flow trajectory was just right to align with the long-fetch of South Holston from the stateline south to south-southwest.

The image below is without any labels and shows the plume well as of 9:00 AM on New Year’s Day, with upslope clouds banked against the High Knob Massif-Tennessee Valley Divide & Clinch Mountain toward the north.

Many interesting features could be seen on the daily Modis Terra Satellite pass, but the South Holston Lake cloud plume was not distinct or had dissipated with a change in the wind trajectory that helped form it this morning.

One reason this has been the coldest New Year’s Day on record ( 19 degrees in 1977 was the former record in Wise; although, to be accurate that was likely due to a carry-over from the 5:00 PM observation time on December 31 and will need to be checked given the former 5 PM daily obs time ) is that snow cover is now widespread between the Ohio River and Canada to allow bitter air to flood south unmodified.

 

Previous Discussion

A light coating of snow, thin glaze of ice, and riming on trees at upper elevations, greeted the final day of 2017.

A general 0.2″ to 0.8″ of accumulation occurred across the area with the freezing drizzle-frozen cloud droplets changing over to all snowflakes overnight into Sunday morning.  The messy mix being regenerated far to the south with a minor shortwave into Sunday afternoon, between the Tri-Cities & Asheville, which have been south of the most bitter air ( note the very tight temperature gradient observed at 7 AM Sunday morning below ).

Sunday afternoon temperatures reflected this pattern, with variations from single digits in the High Knob Massif to the 20s in the Great Valley ( Abingdon through the Tri-Cities ).

With a southern Appalachian snow drought again running this winter, bitter COLD was the dominant feature despite some roads being slick.  Once NW flow cloud bases finally lifted a winter wonderland of beauty was displayed for miles and miles across the high country of the massif.

The main problem being it was just about too cold to enjoy it with air temperatures in the single digits and wind chills below zero throughout the day.  A simple break-down or problem could be extremely dangerous in such conditions, as residents living at elevations above 3000 feet know very well.

Another increase in low-level moisture with arrival of the 850 MB thermal min will help regenerate snow showers and flurries into New Year’s morning, especially along the upslope side of the mountains on northerly air flow.

Although orographic forcing has been weak, and moisture very limited, if nothing else is learned about true arctic air it is that little is required to generate snowflakes-precipitation.  Any low level cloud crossing the High Knob Massif in such bitter air can generate flakes of snow, especially if there is a connection to the Great Lakes.  Upper elevations in the massif have not averaged 75″ to 100″+ of snow per winter season, during recent decades, without this being part of the snowfall regime.

Locations south of 38 degrees North latitude have been in a snow drought along the Appalachian chain due in part to a notable lack of Great Lake moisture transport, especially in favored lifting zones along the western side of the range.

Formation of deep low pressure in the western Atlantic will therefore be important to monitor, since it offers a chance to draw Great Lake moisture south with enough gradient present to produce a mountain torque = upslope snow.

*A much more efficient result would be if the storm were farther west than shown above, to generate better forcing on a cyclonic flow field; however, for snow lovers in a drought any hope for snowfall is better than none.