ALERT For Dense Fog ( Orographic Clouds ) And Unseasonably Chilly Conditions In The Upslope Favored High Knob Massif And Adjacent Upslope Forced ( On SW Flow ) Sections Of The Tennessee Valley Divide Through Much Of Saturday
As low-level winds continue turning toward the SW cloud bases will be dropping into the U.S. 23 Corridor in the Head of Powell Valley and possibly into portions of Norton-Wise ( which have been protected from low bases due to sinking air off the massif ). This will also aid temperature drops within this upslope zone.
Previous Alerts
The Storm Prediction Center Has Issued A Slight Risk For Severe Thunderstorm Development As Remnants Of Harvey Impact The Southern Appalachians
Storm Prediction Center Risk Regions For Friday – September 1, 2017
The main storm threat will be wind damage, to include an isolated tornado risk due to strong low-level wind shear driven by Harvey’s remnant circulation. A notable & increasing temperature gradient will develop late Friday into Saturday as an increasingly cold core develops with transformation into an extratropical cyclone.
Storm Prediction Center – Tornado Risk For Friday – September 1, 2017
Very chilly conditions are expected to develop over the mountains by Saturday as extratropical Harvey draws unseasonably cool air into the Cumberland & Allegheny mountain ranges, which look to experience the burnt of chilly air Saturday into Saturday Night.
Temperatures Saturday will struggle in the 50s at the elevations of Norton-Wise and may hold in the 40s to near 50 degrees at upper elevations within the High Knob Massif during the day, where conditions will feel even cooler due to wind chills.
Friday Afternoon
Periods of showers & thunderstorms. Some storms may be strong to locally severe. Downpours likely. Humid. Winds SSE to SSW at 15-25 mph, with higher gusts. Temperatures from mid-upper 60s to the middle-upper 70s.
Friday Night Into Saturday Morning
Gusty with rain and showers. Turning much cooler. Winds becoming S-SW at 10-20 mph, with higher gusts, on middle to upper elevation mountain ridges-plateaus. Low clouds with dense fog across the higher elevations. Temperatures falling into the mid-upper 40s at highest elevations to the middle 50s to lower 60s ( mildest at lowest elevations ).
Saturday Morning Through Afternoon
Low clouds with dense fog widespread in upslope locations. Chilly. Rain showers and drizzle. Winds SW-W at 5-15 mph, with higher gusts. Temperatures near steady or slowing falling into the 40s in upper elevations and the 50s at middle elevations. Wind chills in the 30s & 40s ( coldest highest elevations ). Milder south into the Great Valley.
Saturday Night Into Sunday Morning
Low clouds with dense fog widespread at upper elevations into most of the overnight. Chilly. Rain showers and any drizzle gradually ending. Winds SW-WNW at 5-15 mph with higher gusts. Temps in the 40s to low-mid 50s. Wind chills in the 30s & 40s ( coldest at highest elevations ).
A very complicated extended range period is upcoming as a deep, autumnal trough digs into the USA. Meanwhile, a Cape Verde born disturbance will be major Hurricane Irma as it approaches the Leeward Islands and Caribbean into next week.
A major push of autumn air is being watched for the mid-later portions of next week. Temperatures will have the potential to drop into the 30s in colder mountain valleys, with coldest sites within the High Knob Massif-Burkes Garden corridor possibly dropping below freezing ( dependent upon cloudiness ).
A cool and foggy Saturday dominated mid-upper elevations across the High Knob Massif where temperatures held in the upper 40s to low 50s, with lower wind chills.
Conditions were not much milder in Norton-Wise, but wind speeds were generally lower.
High Knob Massif Webcam – University Of Virginia’s College At Wise
Rain showers and drizzle continued with rainfall totals of 1.75″ to 2.50″ being common from the head of Big Cherry Lake Basin into the Bark Camp Lake basin with the passing remnants of Harvey.
Previous Discussion
A continuous fall of rain, with occasional downpours, has produced 1.50″ to 2.00″ amounts within the central-eastern sections of the High Knob Massif with the passing remnants of Harvey ( as of Midnight Friday, amid more rain to come ).
High Knob Massif Webcam – University Of Virginia’s College At Wise
Torrential downpours also hit areas around Norton-Wise, with more than 1.00″ of afternoon rain reported by Philip Shelton at his home in the Bean Gap section of Wise.
High Knob Massif Webcam – University Of Virginia’s College At Wise
As typical in this type of flow pattern for the High Knob Massif area, simply outstanding cloud formations were observed throughout Friday.
High Knob Massif Webcam – University Of Virginia’s College At Wise
It now becomes about the chill, as rain continues, with 1:30 AM temperatures down to 52 degrees on Eagle Knob amid SW winds gusting to 25-30 mph ( making it feel cooler ).
