textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Slight increases to temperatures Friday into Saturday as well as to pops Saturday into Sunday.

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 /18Z WEDNESDAY THROUGH MONDAY/

At KCLT and elsewhere: VFR through the period at all but KAVL, where fog/low stratus is likely to redevelop in the mountain valleys. Kept trend of IFR vsby starting around 08z. Cannot rule out an isolate SHRA or TSRA in the vicinity of KAND, but coverage and confidence not high enough to include in the TAF at this time. Winds generally lgt/vrb but favoring WSW at TAFs this evening except KAVL where NW should prevail.

Outlook: Diurnal convective coverage is expected to increase somewhat Thursday, but should remain confined to the mountains. Typical mid-July coverage of diurnal convection is expected to return Friday and continue thru the 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.