010717 Forecast

Mountain Area Forecast ( January 7-10 )

An Alert For ROARING SW Winds In Effect From The Overnight-Predawn Hours Of Tuesday Into Thursday, With Strongest Winds Expected At Middle To Upper Elevations During Much Of This Period.

**Blowing snow from the ground will be a factor overnight into Tuesday, especially at highest elevations.  Some roads will be covered in places which had previously been plowed.
A prolonged period of very windy conditions, with high wind gusts, will be impacting the Cumberland Mountains during the Tuesday to Thursday period ( January 10-12 ).  Despite milder air working into the area, these strong winds will continue to make conditions feel cold Tuesday & chilly through Wednesday.  The strongest winds are expected to come in waves, centered on the daylight and evening hours of Tuesday as well as the Wednesday afternoon into Thursday time period.  Stay tuned for updates.
Dense fog development, with wind driven rains, will also occur Tuesday Night into Wednesday, especially in locations along and southwest of the High Knob Massif & Tennessee Valley Divide.  Rain amounts of 0.50″ to 1.00″+ are expected in the SW upslope flow corridor of the High Knob Landform through Wednesday afternoon ( with added run-off from melting snow ).

*Due to frozen ground and melting snow fog development could become very dense in places and more widespread in coverage than just the upslope flow corridor ( i.e., the Sandy Ridge, Norton-Wise, High Knob Massif & Lee County zone ) as moisture increases by late Tuesday into Wednesday.

ALERT For Bitter Cold Air And Wind Chills Continues Into Sunday – Bitter Air Persisting Into Monday AM – Along With Hazardous Secondary Roads.

Bitter cold will grip the mountain landscape into Sunday.  Wind chills will continue to make bitter temperatures dangerously cold along middle to upper elevation mountain ridges, with 0 to -20+ degree below zero chill factors ( coldest along highest ridges ).
Sunday Night Into Monday Morning will offer the best conditions for extreme temperatures in mountain valleys, with diminishing evening winds.  Temperatures may again plunge to below zero in the colder mountain valleys.  I expect a large vertical temperature spread to develop into the overnight-Monday Morning as SSW-SW winds begin increasing again along higher mountain ridges ( with 20-30+ degree temperature differences between valleys and ridges becoming possible ).  The factor that may limit temperature falls being an increase in mid-high altitude clouds which may help off-set some of the radiational cooling & cold air drainage effects.

Updated: Overnight Into Sunday Morning

Increasing clouds.  Flurries and snow showers developing,  especially along and north to northwest of the High Knob Massif-Tennessee Valley Divide ( on the upslope side of the mountains ).  New snow accumulations of a dusting up to locally 0.5″ to 1.5″ .  Bitter Cold.  NW-N winds 5-15 mph, with higher gusts, on middle to upper elevation mountain ridges.  Temps varying from 5 degrees above zero to -5 below zero, except colder in any snow covered valleys that can develop calm winds.  Wind chill factors of 0 to -10 degrees below zero on middle elevation ridges, with -10 to -25 degree below zero wind chills upper elevation ridges.

Sunday Afternoon

Mostly sunny.  Some increasing high clouds possible late.  Bitter cold.  Light WNW-NW winds.  Temperatures varying from around 10 degrees at highest elevations to the upper 10s to around 20 degrees.  Wind chills below zero in gusts at the highest elevations.

Sunday Night Into Monday Morning

A rapid evening temperature drop, especially in mountain valleys.  Bitter.  Increasing high altitude clouds.  SSW-SW winds developing at 5-15 mph, with higher gusts, during the overnight-morning along higher mountain ridges. A large vertical temperature spread developing with variations from below zero in the colder mountain valleys to readings rising through the 10s into the lower 20s along exposed mountain ridges.

Monday Afternoon

Mid-high altitude clouds.  Becoming windy.  SSW-SW winds 10-20 mph, with higher gusts, below 2700 feet.  Winds SW-WSW 15-25 mph, with higher gusts, along mountain ridges above 2700 feet.  Temperatures in the 20s to lower 30s, mildest in downslope locations from Pound to Grundy.

Monday Night Into Tuesday Morning

Mostly cloudy.  Windy.  SSW-SW winds 10-25 mph, with higher gusts, on mountain ridges-plateaus below 2700 feet.  Winds SW 20-30 mph, with higher gusts, along mountain ridges above 2700 feet.  Temperatures varying from near 20 degrees to lower 30s.  Wind chills in the 10s to lower 20s, except single digits along high mountain ridges.

ROARING SW winds will continue and increase Tuesday, with a chance for rain showers developing.  Wind gusts of 30-50+ mph are expected in the Cumberland Mountains.
A wet and generally mild pattern, with a heavy rainfall potential, is being monitored for later next week into next weekend during the January 12-17 period.  Stay tuned for updates. 


Weather Discussion ( Bitter Cold )

Early Monday Update

Following a new dusting of snow ( up to 0.5″ on High Knob ) into early Sunday the second half of this weekend turned mostly sunny but remained very cold ( as expected ).

Sunday afternoon temperatures struggled toward 10 degrees atop the High Knob Massif and finally reached 19 degrees in Clintwood.  Better than Saturday MAXS, with Joe Carter of the City of Norton Water Plant recording a Saturday HIGH temp of just 14 degrees.  Maximums remained in single digits, of course, atop the massif.
High Knob Massif Webcam – University Of Virginia’s College At Wise

High clouds late Sunday held off long enough to allow colder mountain valleys to plunge below 0 degrees into Sunday evening ( well below zero in high valleys ), with a “balmy” 1.7 degrees being the MIN at lower elevations in Clintwood prior to some rise with increasing clouds.

Winds will be increasing into Monday morning at high elevations, then mixing downward over time into middle and lower elevations.  By Monday Night, and especially Tuesday-Wednesday, SSW-SW winds are going to ROAR.  This will keep conditions feeling cold through Tuesday.


Previous Discussion

*Note: Due to current satellite trends and the latest model trajectories I have added redevelopment of clouds with a chance for flurries and snow showers into the overnight and Sunday morning.  New snow accumulations from a dusting up to locally 0.5″ to 1″ of fluffy snow will also be possible along the upslope side of the mountains, mainly over and north to northwest of the High Knob Massif and Tennessee Valley Divide.

Reference My 010617 Forecast for previous forecast details.
Reference My High Country Focus for information on 2016.
Reference The High Knob Landform for recent work & photos.

Bitterly cold conditions are the now the main weather factor, along with hazardous secondary roads, in wake of the first widespread winter storm impact of the season.

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

Storm Event Snowfall Reports For Jan 6-7
( Snow Depths On Morning of January 7 )

Clintwood NWS Station
4.6″ of Total Snowfall
( 4″ ground depth )

UVA-Wise NWS Station
4.7″ Of Total Snowfall
( 5″ ground depth )

City of Norton Water Plant
5.0″ of Total Snowfall
( 4-5″ ground depth )

Nora 4 SSE on Long Ridge
5.3″ of Total Snowfall
( 5″ ground depth )

High Chaparral of High Knob Massif
5.5″ of Total Snowfall
( 3″ to 6″+ depths )

Eagle Knob of High Knob Massif
6.5″ of Total Snowfall
( 4″ to 8″+ depths )

Wind did not become a factor in this event until the overnight-morning hours of Saturday, when increasingly gusty N winds developed across middle to upper elevations.  This helped reduce differences in total snow amounts between low-high elevations.
Eagle Knob of High Knob Massif At 3:35 PM on January 7, 2017

Temperatures tonight into Sunday Morning are very, very problematic, not due to the cold, but from a forecasting perspective since they are primed and ready to TANK.

Anyone watching me do this forecast live, during the past 1-2 hours can gather that this ( to me ) is the most difficult forecast setting there is ( outside of precip in marginal vertical columns ).  Enough high resolution data has now been collected during the High Knob Massif project at UVA-Wise, in combination with my decades of previous research in these mountains, to understand fully how delicate this setting is with UP and DOWN fluctuations in valley temperatures being typical as winds begin decoupling, then recouple and decouple, etc…it is amazing at times to both experience in person and to also follow with collected data.

*NOTE – Since I originally wrote this the forecast has been simplified by a trajectory from the Great Lakes which will allow for upslope clouds and flurries-snow showers to form into the overnight-Sunday Morning ( January 8 ).  Prior to this the trajectories were shown to just miss the area.  The best valley temp drops are now expected Sunday evening.

Black Mountain Mesonet
*With temperatures at 7:30 PM Saturday hovering around 0 degrees along high mountain ridges it does not take a rocket scientist to figure out that adjacent high valleys could tank if their winds diminish.  Especially given incoming dry air associated with High Pressure.  The key factor will be if the pressure gradient between High and Low pressure can relax by the predawn and morning hours of Sunday ( MINS could occur after sunrise  into mid-morning should that happen ).
Under these type of conditions it only takes a few hours for the literal bottom to drop out of temperatures, so I initially opened up the temperature range in my forecast to account for this.  Then I decided to just note it here, since so many factors are working against complete PBL decoupling in even deep valleys.
NAM 12 KM Model 850 MB Temp-Wind Field Forecast At 7 AM Sunday – Jan 8

A check of the latest NAM Model shows that the local mountains will be close to Great Lake moisture advection  by overnight into Sunday AM, enough to reform upslope clouds, flurries and some snow showers along windward slopes.  So for these reasons, in combo with the pressure gradient, I have decided to hold temps in the 5 above to -5 below range  ( the potential for -10 to -15 below in mountain valleys is certainly there, but likely not to be realized on this night…another shot for it comes Sunday Night ).

NAM 12 KM Model 850 MB Temp-Wind Field Forecast At 1 AM Monday – January 9

While the wind field becomes very favorable for valleys to decouple by Sunday Night, an increase in mid-high clouds may then be the factor to keep the full cooling potential from being realized.  Stay tuned for later updates.