textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

A Heat Advisory was issued for Mecklenburg, Cabarrus, and Union Counties in North Carolina from 11 AM to 8 PM EDT.

SPC removed the Marginal Risk for severe weather from the GSP forecast area for today.

KEY MESSAGES

1. Hot and humid conditions persist through Saturday, with heat indices each afternoon ranging from the upper 90s to lower 100s east of the mountains. Cooler and less humid conditions finally return behind a cold front starting Sunday. 2. A strong cold front brings better coverage of showers and thunderstorms over the holiday weekend. The main day of concern for severe weather is Saturday during the afternoon and evening hours. Drier conditions should return for much of next week.

DISCUSSION

Key message 1: Hot and humid conditions persist through Saturday, with heat indices each afternoon ranging from the upper 90s to lower 100s east of the mountains. Cooler and less humid conditions finally return behind a cold front starting Sunday.

Upper ridging remains over the central and southern United States through Saturday keeping hot and humid conditions around. Heat indices each afternoon will climb into the upper 90s to lower 100s east of the mountains. A Heat Advisory was issued for Mecklenburg, Cabarrus, and Union Counties in North Carolina for today from 11 AM to 8 PM as heat indices are expected to reach advisory criteria. Elsewhere, dewpoints should mix out enough to keep heat advisory criteria at bay. Similar conditions are expected on Saturday but confidence is low regarding another Heat Advisory as dewpoints will mix out again and we will have the potential for better coverage of convection east of the mountains which could further limit heat indices.

Upper ridging retreats westward as upper troughing digs southward towards the Carolinas Saturday into Sunday, with upper troughing lingering over the region through Monday. This will allow a cold front to track across the GSP forecast area late Saturday into early Sunday morning, allowing for the return of cooler temperatures starting Sunday. Monday looks to be the coolest day of the week thanks to surface high pressure building into the region from the north behind the front. Temperatures will then gradually warm again Tuesday onward as yet another large upper anticyclone builds over the southern and eastern United States. Thankfully, both dewpoints and temperatures appear to be lower with this next anticyclone which is nice as we can all agree that we need a break from the heat and humidity (it is September after all). Unfortunately, fall does not officially start until September 22.

Key message 2: A strong cold front brings better coverage of showers and thunderstorms over the holiday weekend. The main day of concern for severe weather is Saturday during the afternoon and evening hours. Drier conditions should return for much of next week.

Main change this update is that the Day 1 SPC Marginal Risk for severe weather was removed from the GSP CWA. This makes sense as the severe threat looks better to our north and east. However, per usual, can never rule out a rogue severe storm this time of year but the chance is very low. coverage of convection will be slightly better this afternoon and evening compared to yesterday but will still be mainly focused over the mountains. Some activity may break containment of the mountains but the 00Z CAMs are in agreement that any activity that manages to push off the mountains will gradually fall apart near the I-85 corridor. So if you are hoping for Mother Nature to water your garden and lawn today (like a certain forecaster) keep your expectations low, especially if you live south of I-85.

Shower and thunderstorm chances will gradually increase over the holiday weekend, with a cold front bringing the potential for strong to severe storms Saturday afternoon and evening. The Day 2 SPC Severe Weather Outlook continues to highlight a Slight Risk (level 2 out of 5) for most areas along and east of I-26. The placement of the slight risk appears plausible as 15-20 kts of 0-6 km shear and 1,500-2,500 J/kg of SBCAPE will be available ahead of and along the cold front Saturday afternoon/evening per the 00Z CAMs. A Marginal Risk (level 1 out of 5) is in place for most locations west of I-26 with the exception of northeast Georgia (as 00Z CAMs show very little in the way of activity Saturday afternoon/evening). 00Z CAMs show two rounds of convection developing, one Saturday afternoon and one Saturday evening. For now, it appears that the severe potential will peak late Saturday afternoon into early Saturday evening. The main hazard with any severe storms that develop is damaging wind gusts but could not rule out large hail up to an inch in diameter.

Shower and thunderstorm chances should return Sunday but the severe threat will be lower due to the lack for forcing behind the front. Drier conditions are expected much of next week as the aforementioned upper anticyclone builds over the region.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

At KCLT and elsewhere: Dry and VFR for terminals east of the mountains through the 12Z TAF period. KAVL still has the potential to see mountain valley fog and/or low stratus develop around daybreak but the window is quickly closing. Restrictions may return at KAVL this afternoon/early evening thanks to better chances for TSRA so introduced a PROB30 from 18Z-22Z. If KAVL does see rain today, then mountain valley fog and/or low stratus could develop overnight into daybreak Saturday. Winds at KAVL should remain calm to light and VRB through most of the TAF period, toggling NW towards the end of the period. Winds east of the mountains will have a southerly component through much of the TAF period, but could go calm to light and VRB at times.

Outlook: Shower and thunderstorm activity should gradually increase through the holiday weekend as a cold front crosses the area. More suppressed weather returns by early next week.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for NCZ071-072-082. SC...None.