Frost will be likely in colder mountain valleys into this morning, as well as tomorrow night into Friday AM when a more widespread coverage will be possible in valleys. Exposed mid-elevation sites, in typical thermal belts, are expected to remain frost free.
Overnight Into This Morning
Mostly clear. Cooler. W-NW winds decreasing to mostly less than 10 mph below 2700 feet. WNW winds 10-15 mph, with some higher gusts, on upper elevation ridges. Temps varying from the 30s in colder valleys to the lower-mid 40s. Wind chills in the 30s along upper elevation ridges.
Partly to mostly sunny. W winds 5-15 mph, with higher gusts. Temperatures varying from the upper 40s at the highest elevations to the middle 50s to lower-mid 60s.
Tonight Into Friday Morning
Mostly clear into the overnight. Increasing high clouds toward morning. Frosty in mountain valleys. Light winds generally less than 10 mph below 2700 feet. NW winds at 10-15 mph, with higher gusts, along upper elevation ridges. Temperatures varying from upper 20s to low 30s in colder valleys to the upper 30s to low-mid 40s ( mildest along mid elevation ridges and exposed plateaus ).
A chance for accumulating snow continues to be monitored for the Palm Sunday Weekend ( centered on March 20-21 ). Prolonged sub-freezing temperatures are expected.
Weather Discussion ( March 16-17 )
Another very nice early spring day was observed across the mountain area Wednesday; albeit, gusty with a significant drying of the low-level air via efficient vertical mixing.
The above scene is focused on Golden Ragwort ( Packera spp. ) whose green basal leaves are shown amid mosses, grasses, a few developing Dandelions, American Beech leaves, and other species.
Afternoon temperature got somewhat warmer than I thought, especially at lower-middle elevations thanks to a boost from downsloping S-SW winds, with a large variation from the 50s at highest elevations in the High Knob Massif, 60s in Norton-Wise-Sandy Ridge, to the lower-middle 70s from Pound to Clintwood to Grundy.
The nearly unidirectional flow aloft, which enhanced vertical mixing and dried the air was key to getting air temperatures in downslope locations above 70 degrees.
This made 7 out of the past 9 days in Clintwood to officially rise above 70 degrees. The last day to do this until next week. Only 2 out of the past 9 days, by contrast, have broken 70 degrees within places above 2700 feet in elevation. No days on northern slopes amid upper elevations, above 3300 feet, have broke 70 degrees. The important off-setting factor for mountain valleys at lower-middle elevations being much cooler nights vs. middle elevation mountain ridges-plateaus.
As my climatology & nature journals show well, the above type of temperature distribution is key to the spring green up pattern featuring the fastest emergence of vegetation amid middle elevation thermal belt zones where MEAN air temperatures are warmer than locations above and below them ( the cooler valleys below them being due to colder nights, while the cooler elevations above thermal belts being due to both cooler days ( high ridges & lofty valleys ) and cooler nights ( especially in high valleys ).
*The Wise and Sandy Ridge plateaus being classic examples of middle elevation thermal belt locations in this area, and long favored for orchards and other early-late season crops which depend upon a longer growing season ( i.e., frost sensitive ).
While temperatures will feel notably cooler today, they get much cooler and just down right cold from Saturday into Sunday-Monday ( especially ).
The flow is also northwesterly, such that any precipitation falling will have a chance to be frozen with some possible enhancement along the windward ( upslope ) side of the mountain chain.
*If this forecast verified it would cause temperatures to remain in the 20s during Sunday-Monday at elevations above 3000-3300 ft, with 30s across lower-middle elevations in the Cumberlands and low-mid 40s within locations downslope amid river valleys of the Clinch, Powell, Holston watersheds toward the Tri-Cities.
More should be known by tonight into Friday as models continue to try and figure out this late season winter setting across the eastern USA.
As typical of March, a week from now the pattern flips again with warmer and wetter conditions ( showers and downpours in thunderstorms become possible ) looking likely by mid to late next week. Stay tuned.