ALERT For Dense Fog Formation Along & North Of The High Knob Massif-Tennessee Valley Divide On NNW-N Upslope Flow Late Saturday Into Sunday Morning For Middle-Upper Elevations above 2500-3000 Feet
9:00 PM Update on Saturday – Very Dense fog has developed above 3400 feet, with freezing fog at highest elevations, on northerly upslope flow. Cloud bases and the freezing level will drop into the overnight and reach down to around the 2500-3000 foot elevation zone.
The latest model trends suggest that any snow accumulations will be restricted to highest elevations, above 3300 feet, and be light, with generally 1″ or less. Little to no snow accumulations are now expected for elevations below 3300 feet.
Saturday Morning-Afternoon
Cloudy skies will give way initially to virga as dry low level air will cause evaporation of Doppler detectable echoes over the area into the overnight. Sprinkles will be possible, with a better chance of showers-light rain developing during the sunrise to mid-morning period.
A good chance for light rain-showers will continue into the early afternoon, with a possible break following during the mid-late afternoon.
Temperatures during the day will be chilly and generally range in the 40s, with dropping temperatures amid dense fog at the summit level of the High Knob Massif ( in 30s ) during the mid-late afternoon.
Saturday afternoon temperatures reached the low 50s in Norton-Wise and adjacent middle elevation communities, with 40s above 3000 feet. The presence of significant dry air in lower levels and lack of enough rain to reach saturation delayed the lowering of cloud bases at upper elevations until after cold air transport got underway after 5:00 PM. A rapid drop in cloud bases occurred following sunset, with dense fog being observed by 9:00 PM at elevations above 3400 feet.
Nora 4 SSE – Official NWS Middle Elevation Observation Site
The lower limit of dense fog formation is yet to be determined, but is estimated to reach within the 2500-3000 foot elevation zone for locations along and north of the High Knob Massif and Tennessee Valley Divide overnight into Sunday morning. Freezing fog at the highest elevations will also drop lower with time as the freezing level lowers overnight into Sunday morning. Some freezing drizzle, drizzle and/or very light snow will also be possible.
*The dense fog and freezing fog level may remain above Wise, but this is yet to be determined overnight into Sunday morning ( if not reaching Wise it will not be very far above ). Caution is advised for those planning on traveling overnight into Sunday morning along roadways that reach above 2500-3000 feet for low visibilities.
Black Mountain MesoNet – Temp Drop And Moisture Increase Since 6:40 PM
Saturday Night Into Sunday Morning
A general NE-ENE wind flow will shift northerly during the afternoon and colder air will begin to arrive by the 5:00 PM to 8:00 PM period at elevations of Norton-Wise. Cloud bases will tend to drop from upper into middle elevations as cold air and low-level moisture combine on northerly upslope.
Any light precipitation developing on upslope flow will fall as drizzle or light snow, with any snow that sticks expected to remain at elevations above 3000 to 3500 feet.
*Some light echoes developing on Dual-Pol Doppler as of 9:30 PM Saturday will move south into the area on northerly upslope flow into the overnight as drizzle or very light snow ( mainly for places along & north of the High Knob Massif-Tennessee Valley Divide ).
Sunday Afternoon Into Sunday Night
Latest model trends suggest some drier low-level air may try to work into the area, with low morning cloud bases-dense fog lifting. If breaks in the overcast occur this could allow temperatures to rise into the 40s to low 50s at lower-middle elevations, with 30s across upper elevations above 3300 feet. This may need to be updated later, as if clouds hold temperatures will be colder than this at all elevations along the upslope side of the mountains ( especially, with respect to NW upslope flow ).
Some flow off the Great Lakes will keep a chance for rain showers, or higher elevation snow showers-flurries, as a possibility late Sunday into Sunday Night.
Weekend Bottom Line
The Bottom Line: Palm Sunday Weekend will be colder than average for this time of year, but any snowfall is looking to be light and mainly restricted to highest elevations above 3300 feet ( with respect to sticking ).
Colder air will begin to arrive late Saturday PM into Saturday Night, with potential for cloud bases to drop and obscure middle elevations along and north of the High Knob Massif-Tennessee Valley Divide in dense fog ( this would impact typical locations subject to dense fog on northerly flow from Wise, and higher locations around Norton, to the ridge communities across Wise and Dickenson counties ).
*Freezing fog will be possible at elevations above 2700-3000 feet.
If drier air works into the area Sunday cloud bases will lift and there could even be some breaks. If this occurs then temperatures will warm more than if clouds hold all day long. The potential for flow off the Great Lakes will keep a chance for rain showers and snow showers in the forecast for late Sunday into Sunday Night. Any accumulations again look to be light.
Weather Discussion ( March 18-20 )
A frosty cold start to your TGIF featured temperatures in the 20s in colder mountain valleys across Wise & Dickenson counties ( 29 degrees being the official MIN in Clintwood ).
*Widespread sub-freezing air temperatures were observed and reported in mountain valleys across the area ( nothing atypical for this time of year, but at least notable in wake of recent mildness ).
Yellow Daffodil ( Narcissus spp. ) In Afternoon Sun – March 18, 2016
The day was again beautiful, with 50s to low-middle 60s across much of the area under mostly sunny skies. I have taken many photographs of Yellow Trout Lilies during this month. During Friday afternoon I came across what was probably the most beautiful one I’d seen ( young and fresh in nice light ).
Beautiful Yellow Trout Lily ( Erythronium spp. ) In Woods – March 18, 2016
Some clouds began increasing aloft toward sunset.
High Knob Massif Webcam – University Of Virginia’s College At Wise
While still looking colder than average, this weekend weather picture is not looking as bad today as it did yesterday and the day before.
GFS Model Total Snowfall Forecast To 8 AM Monday – March 21, 2016
With exception of northeastern West Virginia and extreme northwestern & northern Virginia, models have trended a little weaker with this system. There is some uncertainty remaining, especially with respect to wrap-around and Great Lake moisture transport.
NAM 4 KM Model Total Snowfall Forecast To 8 AM Monday – March 21, 2016
Any accumulations across the southern Appalachians are looking to be at highest elevations, and mostly light, but could be a littler heavier for some places if the low-level moisture is better than currently shown.
An aspect of local concern being the potential for cloud bases to drop into middle elevations late Saturday into Sunday morning to generate dense fog as the colder air is transported across the mountains on NNW-N upslope flow. This would impact Wise & adjacent communities along and north of the High Knob Massif-Tennessee Valley Divide with the most dense fog and poor travel conditions.
As of 9:00 PM Saturday dense fog was down to 3400 feet, with a lowering of cloud bases expected overnight into Sunday morning into the 2500-3000 foot elevation zone. This will either reach Wise or be just above that level by overnight into Sunday morning.
*Freezing fog, with riming, at the High Knob Massif summit level at 9:00 PM Saturday will also drop with time as the freezing level lowers toward 2500-3000 feet into Sunday morning. Prolonged and most significant riming will occur at elevations above 3300 feet through Sunday morning ( with lifting cloud bases expected during the day as temperatures warm into the 30s and 40s ).
