110917 Forecast

Mountain Area Forecast ( Nov 9-12 )

Thursday Night Into Friday Morning

Partly to mostly clear, then becoming cloudy ( low, upslope clouds and areas of dense fog ).  Winds NW-N at 5-15 mph, with some higher gusts, on mid-upper elevation mountain ridges & exposed plateaus.  Turning colder.  Temperatures varying from 20 to 25 degrees at highest elevations to the middle 30s.  Wind chills in the 10s & 20s across mid-upper elevation mountain ridges-exposed plateaus ( single digits and 10s along high mountain crest lines ).

Friday Afternoon

Partly to mostly sunny.  Cold.  N-NE winds 5-10 mph, with some higher gusts.  Temperatures varying from the 20s in upper elevations to the middle 30s to around 40 degrees.  Milder south into the Great Valley.

Friday Night Into Saturday Morning

Mostly clear ( high clouds possible ) and unseasonably cold.  Increasingly large vertical temperature spread developing between cold valleys and milder mountain ridges.   Light & variable winds becoming southerly at 5-10 mph along mid-upper elevation mountain ridges.  Temps varying from the upper 10s to mid-upper 20s, except as cold as 10-15 degrees in colder upper elevation valleys versus temps rising to near or above freezing along high mountain crest lines.

Saturday Afternoon

Sunshine & high altitude ice crystal clouds.  Winds SSE-SSW at generally less than 10 mph.  Temperatures varying from the upper 30s to lower 40s in upper elevations to the upper 40s to lower 50s.

Saturday Night Into Sunday Morning

Partly cloudy ( high altitude ice crystal clouds ).  Large vertical temperature spread between cold valleys and milder mountain ridges.  Winds SSW-SW at 5-10 mph, with higher gusts, along mid-upper elevation mountain ridges.  Temperatures varying from upper 10s to lower 20s in the colder valleys to the 30s to around 40 degrees on exposed mid-upper elevation mountain ridges-plateaus.

A changing upper air pattern across North America and the Northern Hemisphere will increase the potential for a shift into wintry conditions by Thanksgiving week.  Stay tuned for updates on this evolving hemispheric pattern.


Weather Discussion ( Arctic Brush )

A brush with true arctic air is featured during this forecast period in wake of some 36+ hours with dense fog at middle to upper elevations along & north of the High Knob Massif and Tennessee Valley Divide.

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

Check out the HUGE difference in conditions experienced from Wednesday at 5:48 PM ( above ) to Thursday at 5:20 PM ( below ).  Another period with development and drop of low cloud bases is expected into Friday morning as an arctic cold front pushes across the mountains.

A few snow flurries will even be possible in favored upslope locations; although, I have left this out of my forecast above since there will be only a brief period where this could occur with bone dry arctic air surging in behind the arctic front.

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

Although the main push of coldest air will remain to the northeast of the southern Appalachians, this area will get into true arctic air with dewpoints by Saturday morning plunging into 10s at the surface, and as low as -10 degrees Fahrenheit at the summit level of the High Knob Massif.

Under ideal conditions the coldest high valleys could drop into single digits; however, conditions may not be quite ideal with potential for high altitude ice crystal clouds aloft and mixing within the PBL being yet to be determined.  Still the possibility exists for some very cold temps in favored frost pockets with readings dropping under 10 degrees.
European 51-Member Ensemble MEAN 500 MB Height Anomalies: Days 1-5

The upper air pattern does not seem compatible with all the coldness expected in coming days; however, this illustrates that not only do we not live at 500 MB ( around 18,000 feet ) but that the arctic is charging up with bitter air.

European 51-Member Ensemble MEAN 850 MB Temp Anomalies: Days 1-5

This is important since upper air blocking will be changing at high latitudes during the next week to 10 days, such that by the weekend before Thanksgiving, and the week of the holiday, the stage will be set for much colder conditions to develop across the eastern USA.

European 51-Member Ensemble MEAN 500 MB Height Anomalies: Days 6-10

If this trend is real, it will become more evident in forecasts at 6-10 day time frames as we progress through next week.

European 51-Member Ensemble MEAN 850 MB Temp Anomalies: Days 6-10

A key feature above being bitterly cold air across western Canada and portions of Alaska.

I do not know what the upcoming winter will bring when all is said and done ( by next April-May ), but do have increasing confidence that the pattern starting to develop now, and within the next 1-2 weeks, could represent a big-time shift into winter for at least the latter portion of November into December.

My initial feeling is that the potential exists for more winter to occur between now and January 1 than was experienced during the anemic 2016-17 season.  This remains, of course, to be seen and will become more clear as the current pattern changes during the next one to two weeks across the eastern USA.