textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

A Tornado Watch has been issued for northeast Georgia and the western portions of Upstate South Carolina through 2 AM EDT Thursday.

Updated the aviation discussion for the 00Z TAF issuance.

KEY MESSAGES

1. A cold front will bring the potential for strong to severe storms through this evening with the main hazard being damaging wind gusts and a low end tornado threat. A Tornado Watch has been issued for northeast Georgia and the western South Carolina Upstate through 2 AM EDT. Multiple waves of heavy rain through the overnight hours could produce a localized nuisance flood threat as well. 2. Drier conditions Friday and Saturday before rain chances increase Sunday and into Monday. Dry Tuesday and Wednesday.

DISCUSSION

Key message 1: A cold front will bring the potential for strong to severe storms through this evening with the main hazard being damaging wind gusts and a low end tornado threat. A Tornado Watch has been issued for northeast Georgia and the western South Carolina Upstate through 2 AM EDT. Multiple waves of heavy rain through the overnight hours could produce a localized nuisance flood threat as well.

The next round of convection is currently moving across the area as the environmental parameters are favorable for a low-end severe threat. Current mesoscale analysis plots 50-60 kts of effective bulk shear, roughly 250-750 J/kg of SBCAPE, and modest mid-level lapse rates across the CWFA, suggesting organized convection will take part across the area. Low-level shear of 15-25 kts and 100-150 m2/s2 effective SRH will help aid in the very low-end tornado threat with a weak, brief tornado being possible in the Tornado Watch area where tornadogenesis is most favorable. The kinematics will wane over the next few hours, which will lower the overall severe threat. However, modest low-level lapse rates and organized bowing segments should develop isolated instances of strong to severe wind gusts in the strongest storms.

Stout moisture across the area and the expected multiple waves of convection between this evening through the overnight hours could produce a very localized hydro threat. Given the antecedent dry soils and extreme drought conditions, confidence for flooding concerns remains very low. CAMs have a few stripes of 2-4", mainly over the Upper Savannah Valley and southwest mountains of North Carolina where the best chance for training convection is likely through the overnight period. PWAT values over 1.50" in this region will support a good soaking with any storm that moves across this region. The rainfall will be beneficial across the CWFA, with most locations receiving 1-2" of storm total rainfall before the convection moves out of the area by late Thursday morning as the cold front enters the CWFA from the northwest.

The cold front will move across the CWFA during the day Thursday and takes it's time in doing so. Drier air will filter in behind the front, but due to it's slow progression, enough moisture and lift is likely to produce the last round of scattered convection, mainly east of the I-26 and especially over the CLT metro/I-77 corridor Thursday afternoon. Profiles don't support a severe threat, but enough instability will be available for thunderstorms to develop. Afternoon highs will be near-normal outside of the mountains and slightly below normal across the mountains as the CAA works into this region during the daytime hours. Overnight lows will be 4-8 degrees below normal across the CWFA as the cold air settles in following a full fropa. Can't rule out isolated instances of patchy frost in the North Carolina mountains, mainly in the sheltered valleys where boundary layers should fully decouple and temperatures are cold enough before daybreak Friday.

Key message 2: Drier conditions Friday and Saturday before rain chances increase Sunday and into Monday. Dry Tuesday and Wednesday.

Guidance continues to agree on the overall pattern but differs in the details with run to run and model to model inconsistencies. In general, dry high pressure moves in Friday as the Thursday front stalls near the Gulf Coast. Waves of low pressure form along the front and move east Saturday and Sunday. A cold front crosses the area from the northwest on Monday, then dry high pressure returns for Tuesday and Wednesday. Most of the guidance, but not all, agree that Saturday will be dry with better precip chances Sunday or Monday. That said, the latest ECMWF is coming in with only some spotty light rainfall each of those days. Obviously, despite what the model blend has for the forecast, confidence remains low for this period. Below normal temps Friday, rise to around normal for the weekend, back to the low side of normal Monday, and below normal for Tuesday.

AVIATION /00Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: Ongoing SHRA/TSRA and associated restrictions will continue through this evening as multiple rounds of showers and thunderstorms move across the terminals. Thunder chances will wane overnight, but SHRA will continue so included a TEMPO for TSRA and VCTS mention for the best chances through roughly 04Z at all TAF sites. Southwest winds continue through the overnight period with a few instances of gusty winds, especially in the vicinity of stronger showers and thunderstorms. SHRA should continue through the overnight period as multiple rounds continue before pushing east of the area late Thursday morning. Expect MVFR/IFR cigs/vsbys to continue during this time frame. A cold front will cross the region during the daytime period Thursday and winds will turn north to northwest behind it. Timing of the wind shift is noted in the 00Z TAF update. Can't rule out isolated SHRA/TSRA along the front, mainly over KCLT Thursday afternoon with associated restrictions, so kept the PROB30 for TSRA going between 20-24Z. VFR conditions return behind the front by Thursday evening as clouds scatter with drier air moving in. All sites will be north to northwesterly at this point with low-end gusts possible, especially at KAVL.

Outlook: Dry and VFR conditions return Thursday night and Friday. Dry conditions may linger through Saturday night but confidence is low. Another cold front impacts the region late this weekend into early next week bringing another round of rain and associated restrictions.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...None. SC...None.