ALERT For Ice Storm Conditions At Upper Elevations In The High Knob Massif Through Thursday Morning

Caution is advised for those living and traveling across the High Knob Massif, especially at upper elevations above 3000 feet on State Route 619, 706, Routes 237, 238, 704 & others in the high country.  Breaking tree limbs and locally downed trees will be a threat.

Major ice storm conditions are revealed in wake of overnight freezing rain, with a mid-morning change to snow on the 4196 foot summit of Eagle Knob of the High Knob Massif.  Note bent and drooping trees.

ALERT For Strong Rises On Streams Into Thursday PM

While freezing rain and icing is holding back some water, a strong rise is expected on creeks draining the border area of Wise-Scott-Lee counties and adjacent counties along the Cumberland Mountains.  Caution is advised.

*A pocket of cold air aloft will move across the mountains late Thursday into Friday morning to change all lingering precipitation into snow and slowing down run-off.

Expect light accumulations of snow, with a dusting up to 2″ by Friday morning (generally heaviest at upper elevations).

 

Former Alerts

ALERT For DENSE Fog Formation With Dropping Cloud Bases Tuesday Into Tuesday Night For Locations Along And North Of The High Knob Massif-Tennessee Valley Divide On Northerly Upslope Flow.  Caution is advised.

Cloud bases will likely drop as low as the Town of Wise, on northerly upslope flow, with levels as low as 2000 to 2500 feet being possible.  As typical, temperatures will remain milder well below cloud bases in downslope locations of the Clinch, Powell & Holston valleys southeast into the TRI area ( Great Valley and Tri-Cities ).

ALERT For Freezing Fog Beginning At Elevations Above 3500 Feet By 10 AM Tuesday — With Dropping Freezing Levels To 2500 Feet By 7-10 PM Tuesday

Dropping temperatures Tuesday will allow the freezing level to slowly decline from upper into middle elevations during the mid-morning to mid-evening period.  Riming is only expected to be significant at upper elevations.

 

Weather Headlines ( November 11-15 )

*Another significant weather system will begin impacting the mountain area by Monday afternoon into Monday night, with widespread rain.

*Strong rises on creeks draining the High Knob Massif will be possible into Tuesday, where recent rainfall has been significant during November.

*Expect falling temperatures Tuesday as winds shift NW-N with readings dropping into the 20s to lower-middle 30s during mid-late afternoon.  Cloud bases will obscure elevations above 2500 to 3000 feet. 

*A new upper wave renews rainfall by the overnight-to-predawn hours of Thursday, with significant rain amounts.  In addition, icing with freezing rain will also be possible in upslope zones along the High Knob Massif and windward slopes of the Tennessee Valley Divide prior to changing into rain Thursday AM.

Strong rises on streams are expected with saturated conditions already existing, raising the potential of localized flooding.  Creeks draining the High Knob Massif are expected to ROAR into the afternoon.

*A pocket of cold air aloft could support a change to snow by later Thursday into Friday morning with the first widespread, light snow accumulations.

 

Mountain Area Forecast ( Nov 13-15 )

Overnight Into Tuesday Morning

Low clouds, with areas of fog.  Rain redeveloping overnight into the morning.  Winds becoming WNW-NNW at generally less than 10 mph.  Temperatures holding near steady in the 40 to 45 degree range.  Wind chills in the 30s to lower 40s.

Mid-Morning Tuesday Through The Afternoon

Turning colder.  Lowering cloud bases with dense fog at mid-upper elevations ( generally above 2000-3000 feet ).  Freezing fog developing at high elevations, with dropping freezing levels through the afternoon.  Nasty and cold with a chance of light showers-drizzle or mixed precipitation. Winds NW-N at 5-15 mph with higher gusts, especially at higher elevations.  Air temperatures falling through the  30s ( into 20s at high elevations by mid-late afternoon ) in locations along & north of the High Knob Massif-Tennessee Valley Divide.  Wind chills falling into the 20s, with 10s at highest elevations, during mid-late afternoon.

Tuesday Night Into Mid-Morning Wednesday

Low clouds-dense fog and freezing fog.  Chance of flurries or drizzle-freezing drizzle.  Cloud bases will try to lift and break during the overnight to mid-morning period.  Winds NNW-NNE at 5-15 mph.  Cold with temperatures varying from upper 10s to upper 20s ( coldest at upper elevations ). Wind chills in the 10s to lower 20s on exposed mountain ridges and plateaus ( single digits possible in gusts on highest peaks ).

Wednesday Afternoon

Partly-mostly cloudy (mid-high clouds).  Unseasonably cold.  NE-E winds at 5-15 mph, with some higher gusts.  Temperatures in the 30s to near 40 degrees.  Wind chills in the 20s to lower 30s ( coldest at highest elevations ).

Wednesday Night Into Thursday Morning

Rain developing, with freezing rain possible ( most widespread at upper elevations in the High Knob Massif ).  Low cloud bases with dense fog at upper elevations.  Winds ESE to SSE at 10-20 mph with higher gusts along mountain ridges.  Cold with temps in the 30s, except around freezing in colder locations.  The temperature will tend to rise into  the overnight to mid-morning in locations receiving an increase in downslope flow on ESE-SSE winds.

 

Weather Discussion ( NASTY )

A simply nasty weather pattern is gripping the mountain region.  Precipitation began in frozen forms, with freezing temps, at highest elevations within the Cumberland Mountains on Monday (*).

*Especially atop the High Knob Massif and on the peak of Black Mountain, with mixed precipitation amid evaporative cooling.

Initial column cooling was supported by evaporation to drop air temperatures to around freezing during the first hour or two of precipitation, with Doppler radar bright banding also indicating this period aloft.

Tuesday is going to be an even nastier day in terms of dropping temperatures and a damp, bone-chilling feel to the air.  Low-level moisture convergence and a drop in cloud bases along and north of the lifting zone of the High Knob Massif-Tennessee Valley Divide will support the worst, most nasty conditions.

A rather classic orographic upslope flow-adiabatic cooling setting is being forecast Tuesday on weak cold air advection into slopes facing inflowing air along the Cumberland-Allegheny Front.

A prolonged period of riming will occur at high elevations as air temps drop to freezing by mid-morning Tuesday at elevations above 3500 feet.  The freezing level will then decline through the afternoon, eventually dropping to around or below 2500 feet during Tuesday evening.

The next main weather problem develops late Wednesday into Thursday morning, with a strong low-level inversion supporting cold air below 5000 feet.  With ESE to SSE flow this type of atmospheric sounding often supports icing in upslope locations of the High Knob Massif, and along the eastern slopes of the Blue Ridge.

The remainder of the area will have temperatures at or above freezing, with a rising tendency as winds downslope more strongly into Thursday morning.

The icing threat will then diminish in the High Knob Massif and along the Blue Ridge as Thursday progresses and winds change direction in advance of a strong upper-level wave ( below ).

A pocket of cold air aloft associated with an upper-level low and strong PVA ( positive vorticity advection ) will support the potential of the first widespread snow accumulation during Thursday evening into early Friday.

Amounts of 1″ to 3″ will be possible, but stay tuned for later updates on this first widespread sticking of the season.

 

How To Nail Down A Temp Forecast

Reference 110918 Forecast for my actual prediction.

The coldest temperatures of this young 2018-19 cold weather season were observed into Saturday morning, November 10 at high elevations, and Sunday morning within mountain valleys.  Although skies cleared after some flurries and snow showers, conditions continued changing and interacting with complex terrain.

MIN temperatures fell into the 10s at high elevations in the High Knob Massif into Saturday morning, with 0 degree or lower wind chills in gusts on highest peaks.

The atmospheric setting began changing late Saturday into Sunday morning, with dry air & warm air advection at high elevations supporting cold air drainage and a temperature plunge into mountain valleys.

Temperatures actually rose Saturday night into Sunday AM at high elevations, with 30 degrees reported by the mesonet site on Black Mountain at 6:55 AM Sunday (above).  This was down from 32 degrees just over an hour earlier.  MAX temps during Saturday, by contrast, held in the 20s all day at high elevations in the High Knob Massif and Black Mountain.

At the same time, 6:55 AM Sunday, a temperature of 17 degrees was reported by the Weatherbug site at Norton Elementary School; however, it should be noted that the actual air temperature at 5 feet above ground level was in the 14 to 15 degree F range ( the Norton ES sensor is 15-20 feet above ground level next to the school roof and above large asphalt areas instead of natural surfaces ).

Minimum temperatures fell into upper single digits to lower 10s in colder mountain valleys from the High Knob Massif to Burkes Garden, at elevations above 2700-3000 feet, with 11 degrees officially in Burkes Garden.

That is the way to nail down a temperature forecast within complex terrain ( a couple days ahead of time )!