123116 Forecast

Mountain Area Forecast ( Dec 31-Jan 2 )

ALERT For Strong SSW-SW Winds For New Year Eve’s Day ( Saturday ) Is Now In Effect.  ROARING SW Winds Will Develop At Upper Elevations First And Mix Down Into Middle & Lower Elevations Of The Cumberland Mountains During The Day Saturday.

*Following a decrease in winds Friday evening, the gradient tightens again by Saturday morning with another period of ROARING winds ( SW in direction this time ) throughout the daylight hours of New Year Eve’s Day.
A developing temperature inversion late Saturday into Sunday morning, with evaporative cooling, will then restrict strongest winds to highest elevations along top of the planetary boundary layer ( i.e., evaporative cooling will force decoupling as lower levels in the atmosphere cool relative to milder air aloft ).

*The Potential For Snow Or Frozen Precipitation Forms Needs To Be Monitored For New Year Eve’s Afternoon & Evening – Especially In The Southwest Upslope Flow Zone Of Wise, Scott, Lee Counties Along And SW Of The High Knob Massif – Tennessee Valley Divide.

Overnight Into Saturday Morning

Mostly clear.  Cold.  Winds becoming SSW-SW at 10-25 mph, with higher gusts, along middle-upper elevation mountain ridges.  Light valley winds.  Temperatures in the 10s & 20s, varying from single digits to around 10 degrees in sheltered upper elevation valleys to readings rising overnight into morning along mountain ridges ( to low-mid 30s on ridges within the 2000-3000 foot elevation zone ).  Wind chills from single digits & 10s on upper elevation ridges to the teens to lower 20s.

Mid-Morning Through Saturday Afternoon

Increasing clouds with lowering cloud bases over time.  Virga forming aloft with a chance for flurries to light snow developing, especially along and southwest from the High Knob Massif & Tennessee Valley Divide.  Windy & cold.  SSW-SW winds 15-25 mph, with higher gusts, at elevations below 2700 feet.  SW winds 20-30 mph, with higher gusts, along mountain ridges above 2700 feet.  Temperatures varying from upper 20s-low 30s at highest elevations to upper 30s to middle 40s, dropping with the onset of precipitation.  Wind chills in the 10s and 20s.  Dense fog developing at highest elevations.

Saturday Evening Into Sunday Morning

Chance of evening snow ( especially along-southwest of the High Knob Massif-Tennessee Valley Divide ) or mix giving way to rain.  Frozen forms possible in the SW upslope zone.  SSW-WSW winds 10-20 mph, with higher gusts on middle-upper elevation ridges, decreasing into morning.  Temps mainly from the lower 30s to around 40 degrees.  Areas of dense fog.

Sunday Afternoon

Mostly cloudy.  Chance of light showers or drizzle.  Milder.  Winds SSE to SSW at 5-15 mph.  Temperatures in the 40s to around 50 degrees.  Areas of fog, especially at highest elevations along mountain ridges.

Sunday Night Into Monday Morning

Mostly cloudy.  Chance for a light shower or drizzle.  Mild.  Winds SSE-SSW 5-15 mph along mountain ridges-plateaus below 2700 feet.  Winds SSW-SW 10-20 mph, with higher gusts, along upper elevation mountain ridges.  Widespread temperatures in the 40s to around 50 degrees.  Dense fog at highest elevations.

**The potential for a prolonged, harsh period of winter conditions is being monitored for the January 4-6 period, and beyond in time, with formation of high latitude blocking and a cross-polar flow from Siberia into North America.  Stay tuned for updates on this major shift into significant winter conditions in January 2017.


Weather Discussion ( More Nasty )

Reference My High Country Focus for a brief recap of 2016.

Saturday Afternoon Update

Flurries and light snow showers have occurred throughout the afternoon of New Year’s Eve Day across the High Knob Massif area of Norton-Wise ( even at low elevations in the downslope zone to Clintwood ).

High Knob Massif Webcam – University Of Virginia’s College At Wise
Conditions have varied from beautiful mountain waves being visible to a reduction in visibility in light snow-flurries ( below ).
High Knob Massif Webcam – University Of Virginia’s College At Wise

The atmosphere has been saturating from the top down, with the summit levels of the High Knob Massif now being obscured in freezing fog ( clouds ) amid flurries-light snow. A small accumulation has recovered roads.  Travel should be avoided on State Route 619, Routes 237, 238, and others in the upper elevations into this evening as frozen precip will continue at times ( fog will become persistent and lower in elevation to below the main crest lines by late evening ).

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

Winds are simply wicked in upper elevations, with gusts of 40-50+ mph being common.  The 5:15 PM temperature is 29 degrees on Eagle Knob of the High Knob Massif, with 30 at a little lower elevation on adjacent Black Mountain.

Black Mountain Mesonet Up To 5:15 PM – December 31, 2016

Wind have also, of course, been strong in Wise with Lonesome Pine Airport displaying its typical temp bias:

Lonesome Pine Airport At 2684 Feet

versus adjacent stations at the same elevation:

Long Ridge of Sandy Ridge at 2650 Feet

Surface temperatures from just below to just above freezing will continue into this evening within the upslope flow zone of the High Knob Massif area.

At all locations outside the highest elevations there remains a small temperature-dewpoint depression for evaporative cooling.  Temperatures aloft, above the high summits, should continue to warm to strengthen a low-level temperature inversion.  Strong wind gusts at locations below the elevation of Wise should begin decreasing, while gusty to ROARING winds will continue through the night in upper elevations.  Have a Safe & Happy New Year. 


Previous Discussion

Reference my 123016 Forecast page for details on recent snow.
Reference The High Knob Landform for views of December 2016.

Given wind and chilly conditions with developing virga to surface precipitation through New Year’s Eve and Morning, I have updated my forecast page to clean it up for these next upcoming weather conditions.

Black Mountain Mesonet At 4031 Feet – Up To 2:35 AM Saturday ( December 31 )

Winds are beginning to increase again at upper elevations, and this will continue into Saturday with mixing of higher speeds downward into middle and lower elevations with time ( at least until evaporative cooling begins ).

European Model 850 MB Wind Field At 7 PM Friday – December 30, 2016

My main concern for the short-term will be the potential for some snow and frozen precipitation to develop Saturday PM & Saturday Evening, especially in the High Knob Landform corridor where SW air flow rises 1000 to 3000 vertical feet as it streams northeast from Tennessee.  The wind max that is shown above, over the Nation’s Heartland, will be along the Appalachians by New Year Eve Afternoon-Evening.

The High Knob Landform Corridor – Natural Alignment Toward The Southwest
*Low-level cooling will be greater than models suggest into Saturday Evening, even as temperatures continue to warm aloft, so this threat must be monitored until wind direction’s change.
NAM 12 KM Model Forecast Sounding At 7 PM Saturday – December 31, 2016
It is easy to see from this sounding forecast ( above ), that if the surface temperature & dewpoint are just a little closer together at levels downward from the summit of the High Knob Massif ( where orographic lifting occurs ) that the column will be saturated and sub-freezing through a relatively deep layer.  So my concern is a no brainer unless the model is completely out of whack, which is not as likely given current low dewpoint air ( to support cooling ).

Mild air for this time of year will then rule the mountain region from Sunday into Tuesday, with periods of rain, before conditions turn cold once again.

As always, please stay tuned for updates and have a Safe and Happy New Year.