textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Another AQA was issued for Mecklenburg County for Thursday from 10 AM to 8 PM.

Lowered thunder chances through tomorrow as the NBM is running too high.

Updated the aviation discussion for the 00Z TAFs.

KEY MESSAGES

1. Hot conditions will return to the area tomorrow and continue into the weekend. Heat index values will return into the 100 to 105 degree range across the Piedmont Thursday through Sunday. 2. A cold front will approach from the north and bring higher rain chances over the weekend, and slightly cooler temperatures early next week.

DISCUSSION

Key message 1: Hot conditions will return to the area tomorrow and continue into the weekend. Heat index values will return into the 100 to 105 degree range across the Piedmont Thursday through Sunday.

An upper ridge will remain in place over most of the country over the next few days, though will gradually begin to break down late in the the weekend. With the height rises combined with the soupy airmass, temperatures (and associated RH) will rebound tomorrow to several degrees above normal, and a 5-8 degree increase over this afternoon's forecast highs. NBM dewpoints seem just a tad high given the deep mixing to 700mb during peak heating, so have blended in slightly lower dewpoints Thursday afternoon to account for this. Nevertheless, resulting heat index values rise to near or slightly above 100 Friday afternoon, and the current forecast is even higher over the weekend. Heat Advisory conditions may be possible as we move closer to the weekend, especially in the Lakelands and the Charlotte Metro area, but confidence remains low given model handling of the mixed boundary layer. Cannot rule out standard diurnal convection especially across the SW mountains and TN border, and with the increasing heat instability may support isolated pulse severe.

Key message 2: A cold front will approach from the north and bring higher rain chances over the weekend, and slightly cooler temperatures early next week.

The moist surface airmass will remain in place, and by late Saturday a shortwave looks to develop across the Upper Midwest and dive down toward the central Appalachians. Meanwhile, the ECMWF especially is developing a weakness in the eastern Gulf, noted on the NHC Tropical Outlook. The shortwave will push the upper high toward the west, over the Rockies, allowing the upper trough to dig and bring a surface front toward the region. Timing of this front vs the Gulf low may provide additional moisture over the area, or the front may push through before the Gulf moisture is able to push this far north, so confidence in the exact sensible weather pattern remains low. In the current forecast, the upper trough remains over the area through the end of the period with intermittent shortwaves pushing through, with enhanced diurnal pops for late in the weekend and then settling back into a more standard pattern assuming the best moisture from the Gulf low remains to our south and east. Temperatures by Sunday into Monday drop back towards seasonal normals with currently just a slight uptick towards the end of the period.

AVIATION /00Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: Mountain valley fog and/or stratus may develop again overnight at KAVL so went with a TEMPO for IFR vsby and SCT LIFR stratus. Otherwise, dry and VFR through the 00Z TAF period. Isolated to scattered afternoon and early evening SHRA/TSRA should develop Thursday but should remain mostly west of I-26. Thus, maintained dry conditions this TAF cycle as confidence is too low on whether KAND or KAVL will see SHRA/TSRA develop overhead. Winds will be mostly calm to light and VRB through the period. KAVL should see NW/NNW winds at times while most terminals east of the mountains should see W/WSW winds at times. However, KCLT should see winds go W/WNW around daybreak Thursday before toggling more W/WSW Thursday evening. KHKY could see winds briefly go WNW overnight into Thursday morning. Cumulus should gradually dissipate around/shortly after sunset this evening with cumulus returning again Thursday afternoon/evening. Some cirrus may stream across the forecast area as well on Thursday, mainly during afternoon/early evening.

Outlook: Coverage of afternoon/evening SHRA/TSRA will increase Friday but chances appear to be best across the mountains. Even better coverage of mainly afternoon/evening SHRA/TSRA is expected this weekend. Low stratus and/or fog will be possible each morning, mainly in the mountain valleys.

GSP WATCHES/WARNINGS/ADVISORIES

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