textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

WPC introduced a Slight Risk for Excessive Rainfall for today into tonight.

SPC now has the entire GSP forecast area highlighted in a severe risk for this afternoon and evening.

KEY MESSAGES

1. Another round of severe weather is expected this afternoon and evening. Showers and possibly thunderstorms will linger through much of tonight leading to a low-end flood threat. Make sure you have multiple ways to receive warnings, especially if you have outdoor plans. 2. Less hot and humid today with even cooler and less humid conditions expected for the rest of the week. If you have outdoor plans today make sure to stay hydrated and take frequent breaks in the shade or in air conditioning. 3. Rain should linger into Monday before drier conditions return Monday night, lingering through mid-week. A cold front will bring rain chances back towards the end of the week.

DISCUSSION

Key message 1: Another round of severe weather is expected this afternoon and evening. Showers and possibly thunderstorms will linger through much of tonight leading to a low-end flood threat. Make sure you have multiple ways to receive warnings, especially if you have outdoor plans.

The Day 1 Severe Weather Outlook from SPC now has the entire area highlighted in a severe risk for this afternoon and evening. The latest 00Z guidance is showing both higher instability and higher shear compared to the 00Z guidance from yesterday. With 00Z CAMs now depicting 20-30 kts of deep layer shear and 2,000-3,000+ J/kg of SBCAPE, the severe threat should be similar to yesterday, if not slightly more organized. Damaging wind gusts and large hail up to 1 inch in diameter are the main hazards with any severe storms that develop. Timing for severe storms looks to be roughly from 2 PM to 10 PM but could linger later into the evening. Like yesterday, confidence on exact timing remains low.

CAMs have been fairly consistent showing convection lingering into the overnight hours. With wind shear expected to steadily decrease this evening into the overnight, storms will have less movement to them leading to a low end flood threat. Additionally, any areas that received heavy rainfall from afternoon and evening convection will be more susceptible to flooding. As a result, WPC has expanded the Slight Risk for excessive rainfall into a good chunk of the GSP forecast area today into tonight. This expansion seems reasonable give 00Z CAMs are showing the potential for some locations to see 2.5-4.5+ inches of rainfall through 12Z Monday across the heart of the GSP forecast area (roughly from the escarpment up to just west of the I-77 corridor). Localized flash flooding cannot be entirely ruled out, especially for any locations that see multiple rounds of heavy rainfall.

Key message 2: Less hot and humid today with even cooler and less humid conditions expected for the rest of the week. If you have outdoor plans today make sure to stay hydrated and take frequent breaks in the shade or in air conditioning.

Heat Advisory criteria is not expected east of the mountains today thanks to cooler temperatures (compared to yesterday) behind a cold front. But it will still be another hot and humid day, especially across the Upper Savannah River Valley. These areas may flirt with Heat Advisory criteria briefly this afternoon but with the LREF only showing a 20% to 30% chance of reaching advisory criteria today, this is too low to justify an advisory. Furthermore, afternoon storms will likely limit the duration of heat advisory criteria like yesterday.

Relief from the heat and humidity finally arrives Monday with high temperatures expected to end up near or just below normal. Unfortunately, below normal highs will not be here to stay as another upper anticyclone builds over the southern and eastern United States Tuesday into Wednesday. This will allow above normal highs to return starting Tuesday. Luckily it will not be as hot and humid this week as it was last week. The anticyclone gradually breaks down Wednesday night into early Thursday as an upper trough digs across the north central United States. This trough will push across the East Coast Friday into Saturday, dragging a cold front through the GSP forecast area late Thursday night into Friday. High temperatures should peak on Thursday ahead of the front before slightly cooler highs return behind the front Friday into Saturday.

Key message 3: Rain should linger into Monday before drier conditions return Monday night, lingering through mid-week. A cold front will bring rain chances back towards the end of the week.

Upper trough remains over the region through Monday keep showers around. The trough then gets nudged off the East Coast as the aforementioned upper anticylcone builds eastward across the southern and eastern United States. This will allow drier condition to return starting Monday night, lingering through at least Wednesday night. Diurnal mountain convection looks to return Thursday with convective chances returning for all areas Friday into Saturday as a cold front impacts the region.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: Dry and VFR through early afternoon outside of LIFR fog and/or low stratus across the mountain valleys. KAVL and KHKY have yet to see any fog/stratus develop and the window is closing quickly. Another round of TSRA and associated restrictions will impact the terminals this afternoon and evening so have maintained TEMPOs this update. Also maintained PROB30s for SHRA and associated restrictions towards the end of the TAF period as another round of showers will develop and stick around most of the night per 06Z guidance. Could have some embedded thunder at times but confidence remains too low to mention. Winds will be N/NW at KAVL through early afternoon before gradually turning SE/ESE late this afternoon into tonight. Winds east of the mountains will gradually turn more N'ly through daybreak, toggling NE the rest of the morning hours. IFR to MVFR restrictions should develop this evening into tonight but per usual once SHRA starts cigs may improve somewhat. Confidence on timing for TEMPOs and PROB30s remains low as guidance is not in good agreement regarding timing or coverage of TSRA/SHRA.

Outlook: Restrictions, and possibly SHRA, will linger into Monday. Drier conditions return by Monday night, lingering through mid-week. This should allow VFR to return outside of morning mountain valley fog and low stratus.

GSP WATCHES/WARNINGS/ADVISORIES

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