011216 Forecast

My Forecast For Today ( January 12 )

*ALERT For Accumulating Snow Today With Potential For Near Zero-Visibility And Rapid Development Of Hazardous Driving-Walking Conditions Amid A Fast Hitting Cold Front ( Between Noon to 4:00 PM ).

*Locations Along and northwest to north of the High Knob Massif – Tennessee Valley Divide and Clinch Mountain Will Be Favored For The Worst Conditions & Highest Impacts

Generalized Map For Hazardous Snow Burst Impact
Generalized Map For Hazardous Snow Burst Impact

Overnight Into Sunrise

Increasing clouds.  Windy across mid-upper elevation mountain ridges and plateaus.  SSW-SW winds 10-20 mph, with higher gusts below 2700 feet, verses near calm winds in sheltered mountain valleys.  SW-WSW winds of 20 to 30 mph, with gusts to 40+ mph, along mountain ridges above 2700 feet.  MIN temps from 10s in colder mountains valleys, and at highest elevations early, to the 20s.  Wind chills from 10s to lower 20s on lower-middle elevation plateaus-ridges to as cold as 0 to -5 degrees below at the High Knob Lookout.

Sunrise Through Mid-Morning

Mostly cloudy & windy.  Chance of flurries.  Becoming gusty in mountain valleys ( where overnight winds were calm ).  SW-WSW winds 10-20 mph, with gusts to 30+ mph at high elevations.  Temperatures rising into the 20s to lower 30s.  Wind chills in the 10s and 20s, except some single digits at highest elevations in the High Knob Massif.

Mid-Morning Through This Afternoon

Flurries, snow showers and local snow squalls developing.  A burst of intense snow becoming possible from northwest to southeast during the Noon to 4 PM period ( i.e., near zero visibility and rapid development of hazardous conditions ).  SW-WSW winds shifting WNW at 10-20 mph, with gusts to 30+ mph.  Temperatures dropping into the 20s, with upper 10s at highest elevations.  Wind chill factors in the 10s at lower to middle elevations ( 0 to 10 at upper elevations ).

*Localized lightning-thunder is possible amid the cold frontal snow band as it drops southeast through Kentucky into the Cumberland Mountains.  The best chances of this being across northern Kentucky into Ohio and parts of West Virginia.

Tonight Into Wednesday Morning

Chance of flurries & snow showers into the evening.  Becoming bitter with decreasing clouds overnight into the predawn-morning.  W to WNW winds of 10-20 mph, with higher gusts, decreasing across lower-middle elevations overnight.  Temperatures falling into the single digits to lower 10s.  Wind chill factors in the single digits to lower 10s, except 0 to -15 below in gusts on middle-upper elevation mountain ridges & plateaus.

Snowfall Forecast Today Into Tonight

As during the previous event, which I well highlighted, moisture will again be limited with a westerly ( not a NW Upslope Flow ) stream of air from mid-continent into the mountains.  The period for accumulating snowfall will therefore be limited, with most occurring rapidly in association with the cold front and wind shift.

A general 1″ to 1.5″ along upslope side of mountains

Generally less than 1″ on downslope side of mountains

Target snowfall of 1.2″ at 2500 feet ( +/- ) 1″ error potential. This implies that snowfall of .2″ to 2.2″ is possible in Norton-Wise and adjacent communities of similar elevation along the upslope side of the High Knob Massif & Tennessee Valley Divide.  Extremes of a dusting up to 2-3″ are possible.
Snow totals of 1″ or less are expected in downslope locations amid river valleys of the Clinch, Powell, and Holston into the Tri-Cities.


My Forecast Discussion ( January 11-12 )

A bitter start to January 11 featured morning low temps in the single digits to lower 10s, with coldest conditions amid the High Knob Massif where wind chills during the predawn dropped to around 10 degrees below zero over a light snow cover ( generally 1″ or less of depth ).

Eagle Knob of High Knob Massif - January 11, 2016
Wind Blown Eagle Knob of High Knob Massif – January 11, 2016

Afternoon hours of January 11 were chilly with some very nice lenticular wave clouds developing over the High Knob Massif, as featured by the web cam at UVA-Wise.

High Knob Massif Webcam
High Knob Massif Webcam – University of Virginia’s College At Wise
Beautiful waves caught enough moisture to form lenticular clouds above the High Knob Massif, illuminated by the late afternoon sun, as temps reached lower 20s on High Knob and 30 to 35 degrees in lower-middle elevations of the area.
High Knob Massif Webcam
High Knob Massif Webcam – University of Virginia’s College At Wise

It has all been about gusty winds and bitter wind chills during evening hours of January 11 into the overnight of January 12, especially at middle to upper elevations.

Gusty SSW-SW winds have been making it feel like 10 to 15 degrees in Norton-Wise, with even colder conditions along mountain ridges above 2700 feet.

Black Mountain MesoNET
Black Mountain MesoNET ( 10:45 to 11:45 PM on January 11, 2016 )
Wind chills have consistently been in single digits above and below zero along high mountain crestlines, with anyone brave enough to have ventured to the High Knob Lookout experiencing even colder conditions than highlighted above by the somewhat lower elevation mesonet station on nearby Black Mountain.

Focus now shifts to a reinforcing blast of arctic air that will begin pouring into the mountains behind the passage of a cold front during the afternoon-evening of Tuesday.

250 MB Jet Stream Forecast
250 MB Jet Stream Forecast – Left Front Exit Region of 120+ Knot Streak
The area will be in a very favorable position with divergence and rising air amid the left front exit region of a powerful 120+ knot jetstreak in the Polar Stream but, as with the last event, moisture will be a limiting factor and the best overall moisture + lift will remain north of the southern Appalachians.
As the NAM Model forecast sounding below illustrates, the air saturates aloft before it does in low-levels where very dry air is present initially.
NAM Model Forecast Sounding Above Wise
NAM Model Forecast Sounding Above Wise At 1 PM Tuesday
Lapse rates become moderately steep and a little CAPE is present during the favorable early-mid afternoon time period, such that convergence along the front is likely to aid in generation of some convective elements ( graupel snow is often an indicator of strong upward vertical motion associated with convective activity which can occur without actually generating lightning and thunder ).
HRRR Model Forecast Doppler
HRRR Model Forecast Doppler At 1:00 PM Tuesday
The midnight run of the HRRR Model is forecasting a band of snow to be crossing the Virginia-Kentucky border by 1:00 PM, above, and to have some convective type squalls-streaks forming behind it at around 3:00 PM ( below ).
HRRR Model Future Doppler
HRRR Model Future Doppler At 3:00 PM Tuesday

The bulk of snowfall today is likely between Noon and 4 PM, with flurries and snow showers possible before and after this main time period that is targeted for the heaviest frontal and post-frontal activity.

The Bottom Line…Flurries and snow showers will develop today with potential for an intense snow band and/or squalls to form along a cold front during early-mid afternoon ( with brief visibility to near zero and strong, gusty winds ).  For this reason an ALERT has been issued for the possibility of rapid deterioration in driving-walking conditions.

Given recent cold nights it will take only a little snow to cause hazardous travel conditions.
*Winter Weather Advisories have been issued for Dickenson, Buchanan counties in southwestern Virginia and for most of eastern Kentucky and West Virginia.

Make it a safe Tuesday.