Unseasonably cold weather, for May, will continue into Friday. Any snow accumulations are expected to be above 4000 to 4500 feet and mainly restricted to highest peaks from the Smokies to Mount Rogers.
*Colder mountain valleys could drop into the 30s the next few nights, with frost possible if skies can become partly to mostly clear and winds light ( Friday AM and/or Saturday AM having better chances for partial clearing than Thursday AM ).
Overnight Into Thursday Morning
Colder. Chance of drizzle or light rain showers ( mixed at highest elevations ). Dense fog becoming freezing fog at highest elevations. WNW-NW winds 5-15 mph, with higher gusts, on mid-upper elevation mountain ridges-plateaus. Temperatures varying from upper 20s to lower 30s at the highest elevations in the High Knob Massif to the upper 30s to lower 40s. Wind chills in the 20s and 30s along mountain ridges, with 10s in gusts on the highest peaks ( some rime formation possible along the highest ridges-peaks ).
Thursday Afternoon
Mostly cloudy. Chance of rain showers, especially by late, mixed with snow at highest elevations. Local sleet or small hail possible at lower-middle elevations. Chilly for May. WNW to NW winds at 5 to 15 mph, with higher gusts. Temps varying from 30s across upper elevations to the 40s to around 50 degrees ( milder south toward the Tri-Cities ). Wind chills in the 20s and 30s.
Thursday Night Into Friday Morning
Chance of rain showers in the evening ( possibly mixed with snow on highest peaks ). Partly to mostly cloudy overnight with chance of a shower. WNW-NW winds 5-15 mph, with higher gusts, below 2700 feet. NW to N winds 10-20 mph, with higher gusts, along mountain ridges above 2700 feet. Temperatures varying from low-mid 30s to the low-middle 40s. Wind chills in the 20s and 30s, except 10s in gusts along highest ridges.
Friday Afternoon
Mostly cloudy. Continued chilly. Chance of rain showers. Winds NW-NNW at 10-20 mph, with higher gusts, along middle-upper elevation ridges & plateaus. Temperatures varying from the 40s to mid-upper 50s. Wind chills in the 30s and 40s ( coldest at the highest elevations ). Warmer south toward the Tri-Cities.
Friday Night Into Saturday
Mostly cloudy during the evening. Chance of a showers. Then becoming partly cloudy overnight. WNW-NW winds 5-10 mph, with higher gusts, along mountain ridges and plateaus below 2700 feet. Winds WNW-NW 10-15 mph, with higher gusts, along mountain ridges above 2700 ft. Temperatures in the 40s to around 50 degrees, except dropping into the 30s in colder mountain valleys if skies become partly cloudy.
Showers & thunderstorms will become possible as warmer air returns this weekend, displacing the cold, Canadian air mass moving into the region Thursday.
Weather Discussion ( May 4-7 )
Rain became mixed with wet snow at highest elevations in the High Knob Massif during Wednesday Night, with big flakes falling but not sticking ( temp in mid 30s ).
Black Mountain MesoNET During The 4-5 AM Period On Thursday ( May 5 )
Temperatures as of 5:00 AM on Thursday ( May 5 ) have fallen to around freezing atop the High Knob Massif and Black Mountain, with much colder wind chill factors ( in the 10s to lower 20s amid northerly wind gusts in cap clouds…DENSE FOG ).
While it is too early for Blackberries to bloom, Dewberries are in bloom…so maybe this is Dewberry Winter!
Dewberry Bloom ( Rubus spp. ) – May 4, 2016
Due to very cold air aloft, clouds will be abundant by day into Friday with chances for showers ( mixed with snow within highest elevations above 3500-4000 feet and all snow above 5000-5500 feet ). Small hail or sleet will continue to be possible with some of the showers.
High Knob Massif Webcam – University Of Virginia’s College At Wise
Note the puffy, vertically stacked clouds, with cold air aloft. Any sunshine during Thursday and Friday will tend to develop clouds, due to rapid drops in temperature with increasing elevation. At night; however, there will be a chance for clouds to break. If clearing should occur it would allow temps to become colder in mountain valleys with readings dropping into the 30s. Currently, the best chances for this would be Friday AM and/or Saturday AM as the Upper Low moves farther east. A frost or local freeze risk could arise in colder valleys if skies clear for a prolonged period.
NAM 12 KM Model Total Precipitation Forecast Next 48-Hours
Precipitation beneath upper lows can be tricky, with the latest NAM 12 KM Model run forecasting heaviest amounts to remain east of the Cumberland Mountains and southern Appalachians ( in general ) today into Friday ( above ).
Rainfall increases with warm air advection showers and thunderstorm development into this weekend along and west of the Appalachians ( below ).
NAM 12 KM Model Total Precipitation Forecast Next 84-Hours
Very cold air aloft will support the development of numerous showers & thunderstorms, especially from late Tuesday into Thursday. Many will be capable of producing hail. As cold air deepens some snow and sleet will become possible by Wednesday Night into Thursday, especially across upper elevations.
*Some accumulation of snow-sleet will be possible above 3500 feet into Thursday Morning as unseasonably cold air, and wind chills, impacts the mountain region. Some mix of wintry precipitation will be possible at lower-middle elevations.
Overnight Into Tuesday Morning
A chance of rain showers. Areas of dense fog at highest elevations and in places that had heavy Monday rainfall. Winds shifting WNW-NW at 5-15 mph along middle-upper elevation mountain ridges into morning. Temperatures dropping into the 40s to middle-upper 50s ( coolest along highest mountain ridges ).
Tuesday Afternoon
Mostly cloudy. Cooler. A chance of showers. Local thunder possible. WNW-NW winds at 5-10 mph, with higher gusts. Temps varying from upper 40s to lower 50s at highest elevations to the middle to upper 60s.
Tuesday Night Into Wednesday Morning
Mostly cloudy. Chilly. A chance of showers. Local thunder & small hail possible. W-NW winds generally less than 10 mph below 2700 feet. W-NW winds 5-15 mph, with higher gusts, on mountain ridges above 2700 feet. Temperatures varying from upper 30s to lower 40s at highest elevations to the mid 40s to around 50 degrees.
Wednesday Afternoon
Partly to mostly cloudy. A chance of showers and hail producing thunderstorms. SW-W winds at 5-15 mph, with higher gusts. Temperatures varying from the 40s to lower 50s at highest elevations to the middle-upper 60s ( warmest at lower elevations and south toward the Tri-Cities ).
Wednesday Night Into Thursday Morning
A chance of showers and hail producing thunderstorms during the evening. Rain showers becoming mixed with and changing to snow-sleet overnight into morning in the upper elevations ( mixed precipitation possible in middle to lower elevations ). WNW-NW winds 5-15 mph, with higher gusts, on mid-upper elevation mountain ridges-plateaus. Temperatures varying from upper 20s to lower 30s at the highest elevations in the High Knob Massif to the upper 30s to lower 40s. Wind chills in the 20s and 30s along mountain ridges, with 10s in gusts on the highest peaks ( some rime formation possible along the highest ridges-peaks ).
Weather Discussion ( May 2-5 )
The stormy weather pattern that has opened May will be continuing through coming days, with forces driving this storminess shifting toward instability based cold air aloft.
High Knob Massif Webcam – University Of Virginia’s College At Wise
Increasingly cold air aloft will begin to deepen in the vertical during coming days, with a large lapse rate or difference between surface layers and altitudes above 15,000 feet within the atmosphere, where air temps will plunge to -10 to -20 degrees ( Fahrenheit ) below zero.
European Model 500 MB Height Anomaly Forecast – 8 AM Wednesday ( May 4 )
This pattern is simply straight out of winter, with only modification by the time of year ( e.g., high May sun angles, longer days, warmer ground temperatures and low-level moisture via evaporation and transpiration ) working to ease some of the pain of a late season cold blast.
European Model 500 MB Height Anomaly Forecast – 8 AM Thursday ( May 5 )
During May a setting analogous to the heart of winter creates other complicating factors, namely it enhances instability driven by increasingly cold air aloft and lapse rates ( differences in temperature between surface layers and altitudes above 10,000 to 20,000 feet in the free air ).
Numerous showers and thunderstorms will become possible as this instability increases, with many being capable of producing hail as the freezing level aloft drops. Past settings like this have occasionally generated copious amounts of small to medium size hail. A spring example being April 15 in 1998 when VDOT snow plows had to be called out for 3-4″ hail depths on routes such as U.S. 23 and State Route 80.
At a time of year when gorgeous spring ephemeral wildflowers are part of the main show, such a late season blast of cold air might seem unheard of; however, it is actually rather common ( and over the long-term locally gave rise to a May 10 spring planting rule…not to plant tender vegetation prior to this time due to cold air ).
At times the cold air blasts can be substantial enough to support snow, with May falls of snow recently being documented during May 1989 ( 2-4″+ ) and May 1992 ( 2″ up to 2-3 feet ). May snow flakes being most recently observed during May 2005.
It is too early to know what night or nights will be most favorable for valley frost, but an early estimate would be following the break-down of the northerly-northwest low-level flow into the upslope side of the mountains by late Thursday into Friday morning. Stay tuned for updates.
