ALERT For Widespread Freezing Conditions Overnight Into Tuesday Morning With Unseasonably Cold Wind Chills At Mid-Upper Elevations – Another Hard Freeze In Mountain Valleys Tuesday Night-Wednesday AM
*Low relative humidity this afternoon will increase the risk of fires ( although winds will be diminishing ). While it is against the law to burn outdoors until after 4 PM in the state of Virginia, it would be best NOT to burn anything until significant precipitation falls across the region.
A prolonged period of wintry cold, with an accumulating snow potential, is being monitored for late week into this weekend. Significant snow will be possible in upper elevations.
Overnight Into This Morning
Cloudy. Turning unseasonably cold. Chance for a few flurries ( mainly along the upslope side of the mountains ). N winds 5 to 15 mph, with higher gusts, below 2700 feet. Wind N at 10-20 mph, with higher gusts, along mountain ridges above 2700 feet. Temperatures dropping into mid-upper 10s at the highest elevations, with widespread 20s at middle-lower elevations along and north of the High Knob Massif-Tennessee Valley Divide ( milder in lower elevations to the south toward the Tri-Cities ). Winds chills dropping into the single digits and 10s, with sub-zero chill factors in gusts on highest ridges.
This Afternoon
Sunny. Deep blue skies & unseasonably cold. N-NE winds diminishing to 10 mph or less. Temperatures varying from the 30s in upper elevations to the 40s in low-mid elevations ( mid-upper 40s in Norton-Wise ) along & north of the High Knob Massif-Tennessee Valley Divide ( milder 50s south & southwest amid lower elevations of the Powell, Clinch, Holston river valleys toward the Tri-Cities ).
Tonight Into Wednesday Morning
Unseasonably cold. A large vertical temperature spread developing between frosty valleys and milder but windy middle-upper elevation mountain ridges. ESE-SSE winds increasing into the overnight-morning to 5-15 mph, with higher gusts, on middle elevation ridges-plateaus below 2700 feet. Winds S-SW at 10-20 mph, with higher gusts, along upper elevation mountain ridges. Temperatures in the 30s, or rising into the 30s following any evening drops, along exposed middle-upper elevation mountain ridges and plateaus. Temps falling through the 20s within mountain valleys. Wind chills in the 20s on upper elevation ridges.
Weather Discussion ( April 2-5 )
A very active, but continued drier than normal, weather pattern will be turning increasingly wintry heading into late week and the upcoming weekend.
Wind gusts during the early weekend reached 40-50+ mph with up to 17% of Wise County ( on the AEP Network ) out of electricity at one point due to damaging gusts. A continuation of a very windy pattern from March, but now with an increasingly cold turn.
Rough Generalization Of April 1987 Snowfall – Courtesy Of JKL NWSFO
The above graphic is a rough generalization of snow that fell during the great April 2-5 snowstorm in 1987. Snow depths reached 22″ to 24″ in Clintwood ( 33.8″ of total fall measured at Clintwood 1 W ), with 36″ in the City of Norton at the Norton Water Plant ( measured by Gary Hampton ).
A mean snow depth of 4 feet was reported by electrical engineer Carl Henderson, at the WSBN-TV PBS transmitter station atop the Eagle Knob of the High Knob Massif ( Blue Ridge Public Television ). Snow drifts of 5-10 feet occurred in exposed locations. Total snow fall was more than 3-4 feet in the Norton to High Knob Massif area since significant settlement and some sub-snow surface melting occurred during this prolonged upslope event.
Anyone remembering the 1987 snow event, or many other April falls of snow, will not doubt that snow can fall amid the mountains during this time of year.
With 28 years of records, in fact, the mean April snowfall atop the High Knob Massif has been around 7″ with only 4 out of 28 April’s not having measurable snow ( meaning it is more common to have than not to have snow accumulate during April atop the massif ).
European Ensembles MEAN 500 MB Height Anomalies Forecast – DAYS 3-7
The MEAN of the 51-Member European Ensembles are showing that the DAY 3-7 forecast period, from Thursday through this weekend, is looking particularly cold with true winter conditions developing beneath an anomalously deep eastern USA upper air trough ( late season winter cold ).
European Ensembles MEAN 850 MB TEMPS-Anomaly Forecast – DAYS 3-7
The MEAN 850 MB temperature during the DAY 3-7 period has the 0 degrees Celsius ( 32 F ) line south across the Great Smokies in the southern Appalachians, with around -2 C or upper 20s ( Fahrenheit ) air over the High Knob Massif area ( that is the MEAN for the DAY 3-7 period ). In other words, this is air that would be more typical of mean temperatures observed during the winter ( December-February ).
Higher sun angles at this time of year will tend to generate higher day-time temperatures, of course, with an air mass like this verses the low sun angle winter months; however, the fact remains that this will be MUCH below average for April and be cold enough to easily support snow at higher elevations.
GFS Model Total Snowfall Forecast Next 5 DAYS
It is too soon to yet determine actual snowfall totals, but the European Model has consistently been heavier across the southern Appalachians than the GFS Model ( above ).
Meanwhile, the focus is on unseasonably cold air and the need for you to protect any tender young plants that you may have already put out ( hopefully none to few ). Most native plants, such as our ephemeral wildflowers, will be able to with-stand the cold as MANY past events like the April 1987 period have been factored into their DNA.
Pennywort ( Obolaria virginica ) In The Cumberland Mountains
An unseasonably cold Tuesday ( today ) will naturally lead into another hard freeze in mountain valleys tonight, with temperatures falling through the 20s ( coldest valleys could dip into the 10s if mixing from increasing winds above does not disrupt nocturnal temperature inversion formation ).
Meanwhile, following any evening drop, temperatures will tend to rise into the overnight-morning of Wednesday as winds veer ESE-SW and increase in speed along middle to upper elevation mountain ridges ( enhancing a vertical temperature spread between valleys and ridges ).
Showers, with a chance for thunderstorms, develop late Wednesday into Thursday in advance of the big chill down that begins late Thursday into Friday AM.
NAM 12 KM Model Total Precipitation Forecast To 8 AM Friday ( April 8 )
Rainfall remains needed, following a much drier than normal pattern during the past 5 weeks. Surges of low dewpoint air, such as observed today ( Tuesday ), tend to enhance the danger of fires. So please do not burn.
