Reference Early Spring 2021_High Knob Massif for an update on recent and Winter 2020-21 conditions.
ALERT For Heavy Rain And The Potential For Strong-Severe Thunderstorms During Thursday Into Early Hours Of Friday
Waves of rain, with embedded thunderstorms, will develop from Thursday mid-day into the afternoon. Additional showers and thunderstorms will occur Thursday Night into early Friday.
Update At 3:30 PM on Thursday (25 March 2021)
A general 0.75″ to 1.25″ of rain has fallen with this initial wave on headwater creeks from the High Knob Massif into Black Mountain. Those living and driving along streams will need to remain alert for strong water level rises as rain-thunderstorms redevelop.
Specific Point Measurements to 5 PM include:
Birchleaf 1 SW: 0.38″
Clintwood 1 W: 0.41″
Norton (Downtown): 0.70″
Big Cherry Dam: 0.84″
Black Mountain: 0.87″
Eagle Knob: 0.88″
High Chaparral-Robinson Knob: 1.20″
Breaks in the overcast behind this first wave of rain are beginning to create an unstable atmosphere that will become favorable for severe thunderstorms, with possible tornadoes, by late afternoon into this evening.
The SPC Supercell Potential at the Wise Gridpoint increases to 45% by 8 PM, to 60% between 11 PM and 2 AM Friday, then falls sharply to less than 20% after 4-5 AM Friday.
Rain cooled air north of a warm frontal boundary will help limit severe potential during the day. While rotating storms will be possible along the warm front in converging air streams, the main risk will be in the warm sector (between the warm front and cold front) where shear, lift, and instability will be greatest.
The greatest threat for rotating supercell thunderstorms will exist Thursday evening into the overnight hours of Friday (between sunset and 5 AM Friday).
Parameters for rotating storms and tornadoes look to extend farther north and northeast than last week. The Storm Prediction Center may upgrade the region by tonight or early Thursday.
An Enhanced Risk of Severe Thunderstorms with possible Tornadoes has officially been extended northeast into southwestern Lee County, Va., and Bell County, Ky., however, the entire area will be at risk tonight.
The potential for heavy to locally excessive rainfall amounts also exists, with ponding and flooding of low-lying and poor drainage areas, as well as strong rises on streams.
This marks the beginning of a stormy 5-7 day period that could generate widespread 3.00″ to 5.00″+ rainfall totals across the southern Appalachians.
Please monitor NOAA Weather Radio and your favorite media sources for possible watches and warnings that may be needed.
Previous Discussion
Nice early spring weather conditions are expected in the short-term, and while some showers will be possible Wednesday the next chance for significant rain and thunderstorms will hold off until late week.
The main focus for the second half of this weekend into early next week will be on more significant rainfall, with heavy additional rain amounts.