ALERT For Bitter COLD Temperatures Into Sunday Morning With Hazardous Travel Conditions
Temperatures will plunge overnight if low clouds dissipate, with potential for readings to drop below 0 degrees in places that can clear several hours before sunrise over deep snow. Meanwhile, readings will be “milder” if low clouds hold until sunrise.
Overnight Into Sunday Morning
Light snow & flurries into the overnight with partial clearing or clearing possible by predawn hours. Up to 1″ of new snow possible along windward slopes of the High Knob Massif. WNW-NW winds decreasing to generally 10 mph or less by morning. Temps widespread in the single digits and 10s if low clouds can hold, but becoming bitter if skies clear with 5 above to -10 below zero readings possible amid mountain valleys having a deep snowpack.
Mid-Morning Through This Afternoon
Becoming sunny with only a few high clouds possible. Winds SSW generally less than 10 mph below 2700 feet. SW-W winds 5-15 mph along upper elevation mountain ridges. Temperatures mostly in the 20s to lower 30s.
Tonight Into Monday Morning
Mostly clear through the evening. Some mid-high clouds possible by morning. SSE-SSW winds at generally less than 10 mph below 2500 feet. SW-WSW winds 10-15 mph, with higher gusts, along exposed mid-upper elevation mountain ridges & plateaus. Large vertical temp spread between snow covered mountain valleys with calm winds and exposed mid to upper elevation ridges. Temps varying from single digits and 10s in colder valleys to the mid-upper 20s on exposed mountain ridges ( but wind chills in the 10s ).
Weather Discussion ( January 23-24 )
Tonight presents a more difficult forecast for me than the past winter storm, as temperatures are poised to TANK if low clouds dissipate over a fresh, deep snowpack. With northerly upslope keeping the snow machine going along windward slopes of the High Knob Massif at 11:00 PM it might not seem very likely, but must be covered as past climatology dictates ( especially with clearing now just northwest of the Virginia-Kentucky stateline ).
Light Snow & Wind Blown Snow – Eagle Knob at 11:10 PM on January 23, 2016
Wes Ward measured an additional 1.0″ of new snow at the Norton Water Plant at 9:30 PM Saturday evening to bring the storm snowfall tally to 19.1″ at the base of the massif.
City of Norton Water Plant Elevation 2342 feet
January 22 at 9:00 AM 4.0″
January 22 at 4:00 PM 1.8″
January 22 at 9:45 PM 6.0″
January 23 at 3:40 AM 2.0″
January 23 at 9:00 AM 2.8″
January 23 at 3:00 PM 1.5″
January 23 at 9:30 PM 1.0″
Snowfall Total: 19.1″
The 2-day water equivalent total ending at 9:00 AM Saturday was 2.26″ ( not counting what has fallen since then ). Note that 13.3″ of snow fell between sunset Friday and 9:30 PM Saturday after winds shifted to northerly upslope.
*The only measurement that had to be partially estimated was the first one due to a tremendous amount of SLEET which tended to bounce off of the measuring surface. After each measurement the surface is swept clean and made ready to collect what falls until the next 6-hour measurement.
It is not hard to figure what made snow along windward sides of the great High Knob Massif so deep ( from Bowman Mountain toward Big Cherry Lake ) when noting that 13.3″ of snowfall was measured at the City of Norton Water Plant after 4:00 PM Friday when winds shifted north ( snow was much deeper atop the High Knob Massif by 4 PM Friday than it was down in Norton, where heavy overnight precipitation into Friday AM had been dominated by sleet ).
European Model 850 MB Temps & Surface Analysis at 7 AM Saturday
Observe how black isobars above are close together along the Appalachians, with the coldest air in the entire storm having formed right over the southern Appalachians as orographic forcing and lifting worked to chill the air mass. This combined with abundant moisture to keep the upslope snow machine cranking out the flakes ( especially since low clouds-riming existed within prime temperatures for dendritic crystals ).
Saturday was a raw, cold and snowy day with low-mid 10s and below zero wind chills combining with blowing snow to create the worst conditions of this winter so far atop the High Knob Massif, with not a whole lot of improvement down in Norton-Wise and across the adjacent ridge communities of Wise & Dickenson counties.
Nora 4 SSE on Long Ridge of Sandy Ridge
Tonight presents a real dilemma since moisture has decreased to a thin vertical layer with cloud bases now just below and above the summit level of the High Knob Massif, such that the question becomes one of to clear or NOT!
As the big East Coast storm continues to move away the gradient is weakening and low-level winds are forecast to shift more W-SW in lower levels overnight into Sunday Morning. Given a fresh, deep pack of snow, past climatology clearly shows that any clearing can enhance radiational cooling and inversion formation to quickly decouple boundary layer winds and cause temps to TANK.
NAM Model Cloud Forecast For 4 AM Sunday – January 24, 2016
The NAM Model predicts lee side clearing through the TN Valley and along the eastern side of the Appalachians overnight, but the problem is that MUCH more clearing has already occurred west of the mountains than the model indicates.
So low temperatures into Sunday AM will be dependent upon clouds holding or folding, with a large spread possible across the region should upslope clouds hold & downslope locations clear out. Time will tell what happens, and this is the reason my forecast includes clearing as a possibility.
Looking Ahead Through Jan 25-30
A couple of weather systems are being tracked for the upcoming week. The first system is timed for Tuesday.
NAM 12 KM Model 850 MB Temp & Wind Forecast – 7 AM Tuesday ( Jan 26 )
This system is currently forecast to CRANK SW winds along the Cumberland Mountains. It will not be a simple forecast as the current, widespread snowpack will cause low-level temperatures to be chillier than the model is showing.
In addition, strong SW upslope ( if the above verifies ) will also keep temperatures cooler than predicted from Norton-Wise into Big Stone Gap and portions of Lee County.
European Ensembles 500 MB Height Anomalies Forecast – 7 AM Thursday ( Jan 28 )
The second and potentially stronger and much more important system is another wave that will dig into northern portions of the Gulf of Mexico by Thursday.
European Ensembles 500 MB Height Anomalies Forecast – 7 AM Friday ( Jan 29 )
The European Ensembles show that this will be another system to closely monitor, with some members predicting Miller A cyclogenesis ( which could be another significant snow maker for the southern Appalachians ).
The ultimate track of the low pressure will be critical, with spread among the 51-Member ensemble group too large to have any real confidence in a solution at this point in time. However, given it is ensembles and not a single model showing this, an immediate caution flag is raised.
