textproduct: Columbia

WHAT HAS CHANGED

The Heat Advisory has been extended through 8 PM Saturday given the multiple days of elevated heat. Although convection may hamper heating on Saturday, pockets of Heat Index values up to 110 will still be possible.

KEY MESSAGES

- 1. Heat Indices between 105-110 today and Saturday.

- 2. Rain chances increase this weekend and into next week.

DISCUSSION

- 1. Heat Indices between 105-110 today. Less certainty Sat.

Today: Ridging will work to suppress convective development today. With the low convective coverage, much of the area should see highs in the upper 90s or around 100 degrees. Dewpoints will mix into the low to mid 70s, bringing Heat Index values between 105 and 110 for much of the area. A Heat Advisory remains in effect through 8 PM.

Saturday: Ridging breaks down slightly leading to slight height falls over the area. The REFS ensemble members show scattered convective coverage in the afternoon. Although Heat Index values will still be around 105, the convection may cut off heating. This lowers confidence in reaching Heat Advisory criteria on Saturday. However we have extended the Heat Advisory through 8AM Saturday to account for compounding impacts of multiple days with elevated heat and humidity.

- 2. Rain chances increase this weekend and into next week.

The ridge continues to flatten over the weekend and into next week. This should allow for isolated to scattered convection through much of next week. With weak shear over the area we would expect pulse-type convection along with typical summertime chances for isolated downburst winds. Mean PWAT values from global ensembles remain above normal also favoring at least a slight chance of diurnal convection. Models show a decent shortwave moving through the southern Appalachians on Monday with a hot, moist air mass over the CWA. The GFS mixes afternoon dewpoints into the mid 50s and was disregarded. Perhaps this partly explains the extremely low PoPs in the NBM. Instead we favored slight chance PoPs given that this setup would be favorable for potential severe weather if the shortwave moves through during peak heating as currently progged. Through the remainder of the forecast period, we will continue to deal with above normal temperatures and mainly diurnal thunderstorms. Heat Advisories could be needed early next week.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

VFR conditions likely outside of scattered convection this afternoon and evening.

VFR cumulus has developed across most of the area this afternoon, with light west-southwest winds. Another round of scattered afternoon and evening thunderstorms is expected. Convection has already started popping up, so PROB30 groups for -TSRA have been maintained from 18z-24z. Locally heavy rain and gusty winds may result in brief restrictions under any storm. Overnight into Saturday morning, the potential for stratus/fog will once again depend largely on rainfall today. However, the threat for widespread restrictions remains low with light and variable to calm winds tonight.

Similar conditions are expected Saturday, with winds becoming more westerly around 5-7 kts. Another round of afternoon and evening convection is expected, with coverage potentially a bit more widespread.

EXTENDED AVIATION OUTLOOK...Diurnal chances for thunderstorms continue each day through the weekend.

CAE WATCHES/WARNINGS/ADVISORIES

SC...Heat Advisory until 8 PM EDT Saturday for SCZ016-018-020>022- 025>031-035-037-038-041-115-116-135>137. GA...Heat Advisory until 8 PM EDT Saturday for GAZ040-063>065-077.