A Harsh Period Of Winter Weather Is Becoming Increasingly Likely For The January 5-10 Period
An ALERT For Accumulating Snowfall, Hazardous Travel And Increasingly Bitter Conditions Will Be Likely Issued For The Late Thursday Into Saturday Period ( With Bitter Cold Continuing Into Monday )
*I will issue a new forecast by later Wednesday.
Overnight Into Monday Morning
Cloudy. Scattered showers. Areas of drizzle & fog ( dense along upper elevation mountain ridges ). Mild. SSE-S winds 5 to 15 mph, with some higher gusts, along mountain ridges below 2700 feet. Winds S-SW at 10-20 mph, with higher gusts, along mountain ridges above 2700 feet. Temperatures in the 40s to around 50 degrees.
Cloudy. Periods of showers. Thunder possible. Areas of fog ( dense along upper elevation mountain ridges ). SSE-SSW winds 5-10 mph, with higher gusts, below 2700 feet. Winds S-SW at 5-15 mph, with higher gusts, along mountain ridges above 2700 feet. Temperatures widespread in the 50s.
Monday Night Into Tuesday Morning
Periods of rain & showers. A chance of thunder. Local downpours possible. Areas of fog ( dense fog along upper elevation mountain ridges ). Winds SSE-S at 5-15 mph, with higher gusts, on ridges & plateaus below 2700 feet. Winds S-SW at 10-20 mph, with higher gusts, on mountain ridges above 2700 feet. Temps in the upper 40s to low-mid 50s.
A chance of showers, otherwise, partly-mostly cloudy. Unseasonably mild. SW winds 10-20 mph, with higher gusts. Dense fog continuing along high elevation ridges. Temperatures varying from upper 40s to lower 50s amid upper elevations to upper 50s to low-mid 60s ( warmest in downslope sites around Pound, Clintwood, Haysi, Grundy ).
Tuesday Night Into Mid-Morning Wednesday
Turning colder by morning. Rain showers changing to snow by morning at mid-upper elevations before ending. A light accumulation ( dusting ) possible at highest elevations. SW winds shifting WNW-NW at 10-20 mph, with higher gusts, along middle to upper elevation mountain ridges-plateaus. Temps dropping into the middle-upper 20s to mid-upper 30s by mid-morning ( coldest at the highest elevations ). Wind chills dropping into the 10s and 20s.
*Air will turn bitterly cold by Friday into this upcoming weekend. Snow accumulations look likely for the mountains, but amounts remain in question. If substantial snow accumulates the potential for air temperatures to drop below zero will increase, especially in mountain valleys. Sub-zero wind chill factors will be likely across exposed mountain ridges. Stay tuned for updates as this winter weather episode gets closer.
Weather Discussion ( Mild-Nasty )
Reference My High Country Focus for a brief recap of 2016. Additional details will be added later to this reveiw section.
A mild and generally nasty period of weather is on tap through early week as abundant low-level moisture will support periods of light rain, drizzle, areas of dense fog, and even some downpours ( with possible thunder ).
This current pattern is not new, as wet and mostly gloomy conditions have dominated the mountain landscape for the past 10 days with generally mild temperatures ( for this time of year, outside of the NW flow snowfall period ).
Some orographic enhancement of rain will be possible by Monday Night Into Tuesday, with heaviest amounts associated with strong to severe thunderstorms over the Deep South. Time will tell how that may or may not impact rainfall across the Mountain Empire.
While there will be a chance of thunder, due mainly to elevated instability aloft, the risk for severe thunderstorms is currently expected to remain southwest and south of the mountains.
The air mass begins to change & turn colder by Wednesday into Thursday, with a developing streak of light snow on the NAM Model ( above ) being a subject many are already interested in ( yet it remains too far out in time to know how much snow will fall across the mountains ).
*Note that I outlooked the potential for a HARSH period of winter conditions days ago, not because of any given model but due to the synoptic-scale pattern that is developing. Bitter air will come and if snow accumulates this will make conditions much colder, that is true, but bitter air will make conditions harsh regardless of snow for at least a few days.
With respect to snowfall potential, past climatology of settings like this says that two options are most favored:
A ). The northern stream becomes dominant and forces snow generating energy far to the south, with the only moisture source available being the Great Lakes for upslope snow in locations that can get a fetch from the lakes.
B ). Cold air arrives but does not dominate initially, with energy in the sub-tropical jet tracking far enough north to generate a band of potentially significant snowfall. Upslope NW flow snow could then add to amounts along windward slopes in the mountains.
The next couple of days will help determine which scenario will verify, with the MEAN of the 51-Member European Model Group currently going with a snow band development. It should be noted that if one looks at EACH MEMBER the variation forecast is from less than 1″ up to 6-12″+ . The MEAN, which often is closer to true reality, is between these extremes. So it is too soon for anyone to be making an actual forecast of snow amounts. That will come.
Dual blocks will force cross-polar flow into the USA that will make the DAY 3-7 or DAY 4-8 period ( which ever one you wish to pick out ) very cold, with the local mountains being at the -10 C 850 MB isotherm ( that is a MEAN temp of 14 degrees near the High Knob summit for a 5 day period ). That will be cold, of course, at all elevations.
So even if snow does not accumulate it will get cold. If snow cover develops it will become MUCH colder. Stay tuned for updates on this upcoming wintry period.
*Some moderation is currently being shown by next week, but the pattern is one that looks like it can reload. So time will tell more as the setting across the eastern Pacific will be very complex. The Pacific pattern has been forcing our weather, so with limited data points across this expanse it is not surprising that models will be struggling to pin down details of individual systems until they actually reach the North American continent.
Note I say the Pacific has been forcing our pattern, but that Pacific pattern has also been forced by other factors. A key factor appears to have been a rapid and extensive development of snowpack across Siberia during this past autumn that altered the flow field across the northern Pacific and impacted the Polar Vortex.