ALERT For Slick Road Conditions Across Portions Of Dickenson & Wise Counties This Evening
*A band of steady snow has been impacting the Pound to Clintwood corridor, and some other sections, with snow accumulations of 0.5″ or more as of 6:30 PM.
ALERT For Dense Fog Changing To Freezing Fog At Upper Elevations Overnight Into Saturday. A Strong Inversion Will Continue To Trap Low Clouds Across The Area Today. Cloud Bases Will Drop To Near or Below Elevations of The Wise & Sandy Ridge Plateaus Into This Evening ( With Freezing Fog In Locations Where This Occurs ).
The freezing level will drop to around 3500 feet by 5 AM and to 3000 feet by 7 AM, then to around 2000 feet by 10 AM amid better cold air transport into the area at low-levels on WNW-NW winds.
Overnight Into Mid-Morning
Turning colder overnight with rain showers and drizzle changing to snow showers at mid-upper elevations. Light snow accumulation at the highest elevations. S-SW winds shifting W-WNW overnight at 5-15 mph, with higher gusts, below 2700 feet. Winds becoming W-WNW at 10-20 mph, with higher gusts, above 2700 feet. Temperatures dropping into the 20s to low-mid 30s by mid-morning ( upper 10s to around 20 degrees at the High Knob Lookout ).
Wind chills dropping into 10s & 20s, with some single digits at highest elevations after sunrise.
Mid-Morning Through This Afternoon
Cloudy & cold. Chance of snizzle ( drizzle-like snow ) and light snow showers-flurries. Temperatures steady or slowly falling from the 20s to lower 30s ( only small rises possible in downslope locations having any cloud breaks ). WNW-NW winds 5-10 mph, with some higher gusts across upper elevations. Wind chills in the 10s & 20s, with some single digits at highest elevations in gusts.
Tonight Into Sunday Morning
Low clouds. Cold. Areas of light snow & flurries during the evening ( a dusting up to 1″ ), then widespread light snow developing by morning. Temperatures varying from upper 10s to upper 20s ( highest elevations coldest ). Light NNW-WNW winds at generally less than 10 mph. Wind chills in the 10s & 20s, with some single digits at highest elevations.
*Light snow accumulations will occur across portions of Dickenson and Wise counties into this evening, with more widespread light snow developing across the entire area into Sunday.
**The coldest air mass of the 2015-16 Winter Season To Date will push into the mountains late Sunday Night into Monday with air temperatures dropping into the single digits and 10s. A burst of snow will be possible along an Arctic Front into early Monday. Temperatures will likely remain in the 10s from Norton-Wise upward in elevation through the day Monday.
My Weather Discussion ( January 15-16 )
Only a minor update for this afternoon to include a chance for snizzle-like flurries and a few localized and light snow showers amid and beneath the low cloud deck.
Cloud bases are low with dense fog and riming ongoing above 3300 feet in the High Knob Massif.
The only good news, winds are mostly under 20 mph in gusts. Wind chills remain, of course, a factor for anyone out across exposed middle-upper elevation mountain ridges-plateaus.
Temperatures have been steady or slowly falling this afternoon, following a sunrise to mid-morning drop that took the freezing level down to around 2500-2700 feet by 9:00 to 10:00 AM.
As of 2:00 PM the freezing level is down to around 1800 feet for locations along and north to northwest of the High Knob Massif and Tennessee Valley Divide.
Some fine snizzle ( or drizzle-like snow ) and bigger flurries have been falling at times beneath the low, inversion trapped cloud deck in locations along and N-NW of the High Knob Massif and Tennessee Valley Divide into early afternoon.
Light snow, with bigger flakes amid narrow bands, developed during mid-late afternoon and has been sticking some across portions of Dickenson and Wise counties. A dusting up to 1″ of snow will be possible into this evening with upslope activity.
A few roads in upper elevations of the High Knob Massif had become lightly covered by snow as of 5:00 PM. The Pound Gap section of Pine Mountain, on U.S. 23, is another place to also use caution with a more significant band of light snow in that area which is also impacting the Pound to Clintwood corridor.
Temperatures were around 10 degrees colder on the upslope side of the mountains ( e.g., 30 degrees in Norton-Wise verses around 40 degrees in the TRI to Abingdon corridor ) as of 1:30 PM this afternoon ( a few cloud breaks to the lee side and clearing along eastern slopes of the Appalachians in North Carolina ).
It should go without saying, with moisture and temps going below freezing, along with some light snow-flurries, that everyone should be cautious of some slick patches both under-foot and under-wheel this afternoon into tonight.
My Overnight Weather Discussion
The formation of a strong low-level temperature inversion was the big story on January 15. The inversion was created by evaporative cooling as precipitation aloft fell through dry low-level air and effectively cut off milder air aloft.
Rain developed in the Norton-Wise area by around Noon, as expected and forecast, with temperatures in the low 40s at Lonesome Pine Airport dropping into upper 30s.
The same trend was recorded at the official NWS weather station site of Nora 4 SSE, by Wayne & Genevie Riner, with temperatures holding in the upper 30s into evening.
Temperatures along high crest lines of the High Knob Massif and Black Mountain fell from upper 30s down to near and just above freezing with evaporative cooling.
Bright-banding was prevalent on Doppler as snowflakes and sleet mixed with rain as precipitation moved across the massif area.
The only problems reported developed in valleys where a combination of frozen ground, from recent bitter nights, and air temperatures that wet-bulbed ( due to evaporative cooling ) to near freezing created icy patches on ground surfaces in some places amid northern slopes and valleys from Dickenson County into Wise-Scott-Lee counties.
An inversion develops when warm air rests over colder air, and in this case cold air was already present in mountain valleys ( as had been forecast ) by a rather significant nocturnal temperature inversion which formed through evening hours of January 14 into overnight hours of January 15 ( e.g., calm valley conditions that contrasted with gusty ridges ).
In this case the pressure gradient was not strong enough to disrupt the nocturnal inversion before precipitation developed, which initiated cooling via evaporation in relatively dry low-level air to simply reinforce and expand the inversion already present.
Many valleys did not rise out of mid-upper 30s, in wake of the passing rain shield, by contrast with upper 30s to lower 40s on middle-upper elevation mountain ridges & plateaus.
Another important factor, of course, was that the ECMWF ( European ) Model ended up beating all other major models, including both the high-resolution NAM group the GFS Model & GEM, with the main rain shield extending west to along the Virginia-Kentucky border ( e.g., around 0.70″ of rain fell at Big Cherry Lake Dam in the High Knob Massif during the day ).
The inversion is forecast to hold strong today, with warmer air above the level of the High Knob Massif verses colder air from the high crestlines downward in the atmosphere. With a WNW-NW upslope flow this will lock clouds into upslope locations along the Cumberland Mountains and, if sinking in mountain waves is not strong enough then it will likely hold clouds in also to the lee amid river valleys of the Clinch, Powell, and Holston.
*WNW-NW flow today will be weaker than during previous days as the area is in between weather systems. This will make mountain waves less likely to mix out the inversion ( if the model forecast of it’s strength is accurate ) amid downslope flow locations.
Focus now shifts to a wave developing over the northern Gulf of Mexico late today into Sunday. This is the type of setting which snow lovers dream about; however, in this case it does not look to be a big snow maker. There is still time, of course, for lovers of the white to hope!
The latest European Model is a little farther north with the wave than the NAM, and would generate some light snow across the southern Appalachians into Sunday morning.
This is a Miller A “wanna-be” that likely will not track far enough north nor deepen ( intensify ) or phase fast enough for any major snowfall impacts. It does, as always, bear close watching on new runs through today. Stay tuned.
*A system moving through the southern stream that does have potential to become the first winter storm of this season will also bear close watching for the middle to latter parts of next week, centered upon the January 20-23 period.