textproduct: Columbia

WHAT HAS CHANGED

Minimal change to heat headlines today. A bit more convective coverage possible Sunday. Aviation discussion updated for 18z TAF issuance.

KEY MESSAGES

- 1. Heat Index values between 105-110 are expected this afternoon, elevating the risk of heat related illnesses.

- 2. Severe storms possible late this afternoon and evening.

- 3. Another round of severe storms are possible Sunday.

DISCUSSION

KEY MESSAGE 1. Heat Index values between 105-110 are expected this afternoon, elevating the risk of heat related illnesses.

Highs today are expected to be in the upper 90s to around 100 degrees today. Although we will be near daily records at CAE/AGS (101F at CAE and 102F at AGS), temperatures may fall just shy. A front will continue to work toward the area from the north, with afternoon dewpoints likely remaining in the upper 60s to mid 70s in some spots ahead of it. This is expected to yield widespread heat indices likely falling between 105-110F. The uptick in outdoor activities today will bring much a much higher risk for heat related illnesses, so proactive measures to stay hydrated and remain cool should be taken. A Heat Advisory will be in effect starting at 11am, continuing until 8pm for the whole CWA.

Convection is still expected to hold off until the late afternoon into the evening. Cannot rule out a few spotty showers or storms earlier, but confidence in this is low.

KEY MESSAGE 2. Severe storms possible late this afternoon and evening.

A shortwave will continue to spark convection to our north today as the disturbance carries east into eastern NC late today. As thunderstorms move from the southern Appalachians and into the SC Piedmont this afternoon they will encounter a relatively dry air mass but with very steep low level lapse rates. This environment would be conducive for damaging winds with large CAPE profiles (mlCAPE near 2500 J/kg) and DCAPE values near or over 1000 J/kg.

Overall, the forecast is on track where the bulk of convection is expected mainly after 21z as better forcing and the aforementioned batch of storms attempts to push into the northern FA. However the CAMs show the more organized storms breaking up as they move into the drier air mass to the south and the better dynamics remain to the north. Although this will limit the threat of widespread severe weather we can still expect a chance of isolated to scattered storms which would cause damaging winds. The highest confidence will be across the northern Midlands where storms could push in before loss of heating. As outflow continues to push south through the area overnight we could see additional storms develop through the night but the chance of severe weather is lower.

KEY MESSAGE 3. Another round of severe storms are possible Sunday.

A weak surface boundary is expected to slowly sag through the FA Sunday. Compared to previous day's forecasts the boundary is expected to be further north, allowing for more widespread thunderstorms as a prominent shortwave moves into the area in the afternoon. By mid day, the boundary could still be bisecting the CWA. Atmospheric moisture will be higher than the previous day with PWAT values close to 1.8 to 2 inches. As shortwave energy moves into the region expect, scattered to numerous storms to develop, especially along and south of where the boundary ends up. Forecast soundings support a downburst wind threat with mlCAPE values from 1500 to 2000 J/kg and DCAPE values close to 1000 J/kg. Lingering cloud cover could put a damper on this environment, especially in the northern Midlands, but if clearing is seen the potential for severe storms will be higher.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Mainly VFR expected with possible convection later this afternoon into tonight. Some fog/low stratus possible near daybreak.

Cumulus has started developing across the area this afternoon with bases around 5k ft. Late afternoon convection is expected to move into the area as a disturbance to our north carries thunderstorms and showers from the southern Appalachians and into the SC Piedmont this afternoon. However, drier air in our CWA could limit coverage as they move closer to the terminals. For now, PROB30 groups have been included at all sites with convection occurring roughly between 20z-03z. The highest confidence will be at our northern terminals where storms could push in before loss of daytime heating.

Winds should become light and variable overnight under mostly clear skies. There is potential for fog or low stratus at the terminals between 09-14z on Sunday. Conditions will continue to be monitored tonight for the need for additional widespread restrictions.

EXTENDED AVIATION OUTLOOK...Chances for restrictions and thunderstorms continue Sunday. Diurnal storm chances continue early next week.

CAE WATCHES/WARNINGS/ADVISORIES

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