Mountain Area Forecast ( Oct 15-18 )

Widespread Frost And Freezing Conditions Are Expected Tuesday And Wednesday Mornings In Mountain Valleys And Other Typical Cold Pockets Upon The Wise & Sandy Ridge Plateaus

Widespread frost, as well as areas of below freezing conditions, are expected Tuesday and Wednesday mornings across Dickenson, Wise, and adjoining counties toward Tazewell.  Major river valleys prone to fog, and a few mid-elevation thermal belt sites, may be able to remain above freezing but precautions should still be made to protect any cold-sensitive late season plants.

Hard freezes are expected in typically cold mountain valleys on multiple nights throughout this week, with coldest valleys from the High Knob Massif to Burkes Garden dropping into the 20 to 25 degree range on colder nights.  Tuesday Night into Wednesday AM is looking to have the best cooling conditions in high valleys.  The growing season ended in these locations during early October.

*October 17 NOTE – Let me make it crystal clear about the extent of frost which was WIDESPREAD and NOT patchy in mountain valleys on the morning of October 17.

Route 83 – Morning frost was continuously visible from Clintwood into Pound, except for the rise through Red Onion Mountain Gap. 

Frost was visible from Pound to the foot of Wise Mountain, along U.S. 23, then absent from the mountain.  Frost was visible in Wise, except for exposed portions like Lonesome Pine Airport.  Frost was then continuous from Norton to Coeburn along Alt. 58.

When you can drive for MILES and see frost that = widespread in valleys.  When you see frost in a valley, then have to drive for a mile, or miles, before seeing anymore then that = patchy.

AM Mins on October 17 were in the upper 20s to lower 30s in most valleys, except even colder in favored high valleys of the High Knob Massif.  More of the same will be seen into morning hours of October 18, with even drier air in the vertical profile ( some high clouds will decorate skies overnight into Wednesday AM ).

Overnight Into Sunday Morning

Mostly clear to partly cloudy, except low clouds with dense fog ( orographic clouds ) at upper elevations within the high country of the High Knob Massif and along high elevations in the Black mountains.  Winds S to SSW at 5-15 mph, with higher gusts, along mountain ridges-plateaus below 2700 feet.  Winds SSW-SW at 10-20 mph, with higher gusts, on middle-upper elevation mountain ridges above 2700 feet.  Temperatures varying from upper 40s to low 50s in valleys protected from winds, to the lower 60s.

Sunday Afternoon

Low clouds in upslope areas ( becoming cloudy in downslope locations ).  Windy in higher elevations.  Showers becoming likely by late, with a chance of thunder.  Temperatures from 60s in upslope locations ( Norton-Wise ) to the lower-middle 70s in downslope sites ( Pound-Clintwood-Haysi ).

Sunday Night Into Monday Morning

Evening rain likely, with a chance of thunder.  Downpours.  Rain diminishing to drizzle overnight.  Turning much colder with dropping cloud bases on NNW-N winds ( bases possibly dropping to elevations of the Wise & Sandy Ridge plateaus ).  Temperatures dropping into the 40s, except 30s in upper elevations ( to around freezing on highest peaks ).  Wind chills dropping into 20s to low 30s at highest elevations.

Monday Afternoon

Becoming partly to mostly sunny.  Chilly.  N winds 5-15 mph with some higher gusts.  Temperatures varying from low-mid 40s in upper elevations to the low-middle 50s ( milder south into the Great Valley ).

Monday Night Into Tuesday Morning

Mostly clear.  Cold.  NE-ENE winds 5-10 mph, with some higher gusts, along mid-upper elevation mountain ridges.  Temperatures varying from 20s in colder valleys at upper elevations to the low-middle 30s.

Tuesday Afternoon

Mostly sunny.  Deep blue skies.  Light NNE-E winds.  Temps varying from low-mid 50s in upper elevations to the lower to middle 60s.

Tuesday Night Into Wednesday Morning

Mostly clear ( some high clouds overnight ).  Cold.  Light winds.  Frosty cold in mountain valleys with a large vertical temperature spread between valleys and ridges.  Temps varying from upper 20s to lower 30s in valleys, except 20 to 25 degrees in coldest valleys of the High Knob high country and Burkes Garden, to upper 30s-middle 40s along exposed mid-upper elevation mountains ridges and plateaus.

Reference My History Of Autumn Color 2017 for an update on color changes & recorded temperatures in the High Knob high country.

 

Weather Discussion ( Colder Air )

Sunday Afternoon Update

It has been an interesting Sunday along the Cumberland Mountains, as often is the case in this type of setting.

Low clouds and dense fog ( orographic cap clouds ) obscured high elevations in the High Knob Massif overnight into Sunday.  Note clear skies, by contrast, in the downslope sector across northern Wise County and most of Dickenson-Buchanan counties where SSW air flow was sinking ( above view ).

This was a windy, chilly feeling air flow atop the high country versus calm winds down in lower elevations ( where the AM MIN reached 50.7 degrees at Clintwood 1 W amid calm conditions ).

Low clouds banked up along the High Knob Massif – Black Mountain corridor held temperatures in the 50s atop the high country of the massif until early afternoon, while abundant sunshine to the north allowed readings to rise upward into the 70s in Clintwood.

As rising air with convergence along a strong front to the west propagated closer to the mountains, enough sinking air finally helped to dissipate clouds along all but the high crest lines into late afternoon.

Sunday afternoon MAX temps varied from low 60s atop the High Knob Massif to 78 degrees in Clintwood ( following the morning low of 50.7 degrees ).  Temps also rose into the 70s in Norton-Wise with increasing sunshine by 2:00 PM.

 

Previous Discussion

The coldest air mass of the autumn season, to date, will be pushing into the mountains by Monday.  Showers, with a chance of thunder, will become likely by late Sunday into Sunday evening.  Locally heavy rain, with orographic cap clouds, will be possible in favored upslope locations.

Although not resolved exactly as it should be, a signal for locally heavy rain is being picked up on by terrain models ( below ).  This has added support by the early formation of orographic cap clouds in upper elevations of the High Knob high country.  Rainfall totals may reach 1.00″ in favored upslope zones, with lesser amounts in other locations ( the western side of the Appalachians being most favored for heavier rain amounts in this type of setting ).  Any thunderstorms that form could skew the rainfall pattern.

Orographic clouds, with dense fog at highest elevations, began developing with upslope SW flow into the High Knob Massif and Black mountains by late Saturday Night into the early overnight of Sunday.

This is well in advance of a strong front that will be reaching the Cumberland Mountains by late Sunday.

Convergence along the cold front, which is shown vividly below, will be just west of the mountains by 8 PM Sunday if the NAM Model timing is correct.  Regardless, convergence is the important feature that will combine with relatively narrow but rich moisture to develop downpours as the boundary pushes into the mountains.  Any storms that develop could skew the rainfall pattern, as noted above.

A shift to northerly upslope flow, combined with a band of lingering moisture behind the frontal boundary, will likely drop cloud bases lower ( into the middle elevations ) by late Sunday Night into overnight-predawn hours of Monday amid significant cold air transport.

The focus then shifts to building High Pressure and very dry air that will set the stage for widespread frost and freezing conditions across the mountains into Tuesday morning.