textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

The aviation discussion updated for the 12Z TAF issuance.

KEY MESSAGES

1. One last dry day today. Then humidity increases on Wednesday along with daily shower and thunderstorm chances that continue through the rest of the week.

DISCUSSION

Key message 1: One last dry day today. Then humidity increases on Wednesday along with daily shower and thunderstorm chances that continue through the rest of the week.

Dry high pressure will linger over the area today, as an upper trough begins to flatten out over the eastern US. Dewpts will once again mix out into the upper 50s to lower 60s, and fcst soundings continue to remain stable. Highs will similar to yesterday, right around normal.

The pattern starts to change Wednesday, as a vigorous upper shortwave trough dives into the Midwest and carves out a new longwave trough across the OH/TN Valleys. Flow will back to S/SWLY in response and advect moisture back into the forecast area. Dewpts are expected rise into the upper 60s to around 70 Wednesday aftn, while temps remain near normal. The atmosphere should become moderately unstable, and mountain-top convergence should trigger deep convection. A warm front will activate across the I-20 corridor and start lifting north into the CWFA Wednesday evening. So PoPs ramp up into the solid chance range across the Piedmont, roughly from south to north, as the front helps trigger more convection. Convection may linger into the overnight, but latest guidance seems to backed off the overnight PoPs a tad. Thursday still looks like the most active day, as PWATs surge to around 2" with the warm front basically stalling out across the Piedmont. There may be a lot of cloudiness to start the day, but enough scattering out should result in decent sbCAPE and 20-30 kt of 0-6km bulk shear to support at least a marginal severe weather threat Thursday aftn into Thu evening. Excessive rainfall and isolated flash flooding cannot be ruled out as well. PoPs continue to be in the likely to categorical range Thursday, and have increased into a similar range on Friday, as guidance has trended wetter.

A cold front should push into the area from the NW on Friday, then stall out just to our east Saturday. PoPs gradually decrease over the weekend, as dry air tries to filter in behind the front. An upper ridge will begin to build in from the Southern Plains Sunday into Monday, further drying out the CWFA and allowing temps to warm to slightly above normal with some lingering humidity. The heat index may push into the 90s across much of the Piedmont Sunday and Monday, possibly reaching 100 in parts of the Upper Savannah Valley and southern Upstate on Monday.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

At KCLT and elsewhere: A few to sct high-based Cu field is expected during the afternoon and may linger into tonight. Some guidance is hinting at lower-level clouds forming across the Midlands and possibly expanding north toward the terminals. As of the 12z TAF issuance, confidence is too low to mention anything lower than VFR-level. KCLT may see cigs around 5000 ft mid-to-late Wednesday morning. Wind will be light thru the period, mainly out of the N/NE thru around midday, then become more VRB in the aftn and thru tonight. Except at KAVL, where it should favor a S direction. Wind should toggle to SE over KCLT Wednesday morning.

Outlook: SHRA/TSRA could return to the western terminals Wednesday afternoon. A better chance of SHRA/TSRA is forecast Wednesday night through Saturday. Mountain valley fog and low stratus is possible each morning.

GSP WATCHES/WARNINGS/ADVISORIES

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