textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Temperatures continue to trend slightly cooler late this week and into next weekend.

KEY MESSAGES

1. Hot and humid conditions with heat index values reaching 100 to 105 degrees outside the mountains this afternoon and evening. Elevated heat index values continue thru Wednesday. Cooler temperatures later in the week should provide some relief from the heat. 2. More scattered showers and thunderstorms are expected this afternoon and evening, with some strong to severe thunderstorms likely. Damaging winds are expected to be the main hazard, however heavy downpours could also produce some localized flash flooding. Scattered convection continues on Monday with more severe storms possible. Less convective coverage is anticipated on Tuesday, before a weak cold front brings increased coverage and the potential for more severe weather on Wednesday.

DISCUSSION

Key message 1: Hot and humid conditions with heat index values reaching 100 to 105 degrees outside the mountains this afternoon and evening. Elevated heat index values continue thru Wednesday. Cooler temperatures later in the week should provide some relief from the heat.

Despite broad upper trofing to our north and sct showers and thunder- storms this afternoon/evening, highs are still expected to reach the low to mid 90s again today. With dewpts remaining elevated, heat index values over 100 degrees are also expected across much of our lower terrain. A few locations may briefly reach 105, but they should be isolated enough to preclude a Heat Advisory. Highs cool a bit more on Monday but increase slightly again on Tues. Max heat index values will mostly be 100 degrees or less Monday, but with the increased temps and lingering elevated dewpts Tues and Wed, max heat index values increase back over 100 for many locations along and south of the I-85 corridor. Spotty 105 values appear possible Tues, but the probability of needing a Heat Advisory still appears low at this time. The heat and humidity finally diminish by Thurs with an airmass change behind a cold front. Until then, stay hydrated, take frequent breaks in air-conditioned or shaded areas, and never leave children or pets unattended in vehicles.

Key message 2: More scattered showers and thunderstorms are expected this afternoon and evening, with some strong to severe thunderstorms likely. Damaging winds are expected to be the main hazard, however heavy downpours could also produce some localized flash flooding. Scattered convection continues on Monday with more severe storms possible. Less convective coverage is anticipated on Tuesday, before a weak cold front brings increased coverage and the potential for more severe weather on Wednesday.

Broad upper trofing centered over the northeast will push a weak front into our fcst area from the north today. The atmosphere will become very unstable with an increase in bulk shear from the trof and front. High PW values and steep low-level lapse rates will create an environment favor- able for damaging downbursts. The increase in shear could help organize some of the convection which could increase the severe storm potential. Accordingly, SPC has a Slight Risk area over most of our CWA for today. The front stalls over the Carolinas on Monday, but the shear is expected to weaken. Nonetheless, the atmosphere will remain very unstable with high PW values and steep low-level lapse rates. SPC has a Marginal Risk for severe storms across the majority of our fcst area on Monday. Diurnal convective chances linger on Tuesday, but the overall coverage should be lower, especially outside the mtns. Coverage will likely increase again on Wednesday as another upper trof amplifies over the eastern CONUS and moves yet another cold front into our area. Severe storm potential may also increase again on Wednesday. More typical diurnal convection returns by the end of the week.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

At KCLT and elsewhere: Similar coverage of showers/thunderstorms is likely again this afternoon/evening, with the best coverage expected in the vicinity of KAVL and KHKY. As such, they have VCSH with a TEMPO for TSRA from roughly 18 to 22z. I kept PROB30s for TSRA at KCLT and the Upstate terminals for the aftn/evening convection as they are less likely to be directly impacted. There is a good chance of mtn valley fog again overnight and a decent chance it will reach KAVL. Otherwise, winds outside the mtns will remain SW to WSW thru the evening, going light to calm overnight. They will pick up from the SW again tomorrow afternoon. Winds at KAVL will likely remain light and VRB this aftn/evening, becoming calm later tonight. They will be light and SLY tomorrow aftn.

Outlook: Good coverage of afternoon/evening SHRA/TSRA continues Monday with less coverage expected on Tuesday. Coverage is expected to increase again on Wednesday then decrease Thursday. Low stratus and/or fog will be possible each morning, mainly in the mtn valleys.

GSP WATCHES/WARNINGS/ADVISORIES

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