textproduct: Columbia

WHAT HAS CHANGED

A severe thunderstorm watch has been issued for the entire CWA until 9 PM EDT. Thunderstorms will develop this afternoon and could produce damaging winds and localized flash flooding. 18z Aviation.

KEY MESSAGES

- 1. Severe weather and flash flooding possible today.

DISCUSSION

KEY MESSAGE 1: Severe weather and flash flooding possible today.

The severe weather threat is winding down across the forecast area this evening. There were numerous strong to severe thunderstorms across the area this afternoon, with the bulk of them shifting eastward as of this writing. There is an interesting cluster of storms developing in the rain cooled air in Calhoun/Orangeburg/Clarendon counties right now, so the storms are likely to persist for a bit in our eastern counties. But in general, things should be winding down over the next couple of hours.

An upper trough will dig in on Saturday, with the axis shifting farther east. This will allow direr air to begin moving into the western portion of our FA this weekend. However, deeper moisture and moderate conditional instability along the coast could support another threat along the coast for microbursts and damaging winds in the afternoon, particularly near the I-95 corridor. Beyond that, a more seasonal pattern is expected to develop, with temperatures closer to normal, increasing humidity, and daily chances for isolated to scattered showers and thunderstorms.

AVIATION /00Z SATURDAY THROUGH WEDNESDAY/

VFR conditions are present at all TAF sites currently as convection and stratiform rainfall pushes eastward and out of the forecast area. IFR and LIFR ceilings (and possibly visibilities) are forecast later tonight and into Saturday.

Convection continues to push eastward out of the forecast area, leaving the TAF sites sitting underneath VFR cloud cover. While there was a lot of rainfall in several parts of the forecast area, the heaviest rain generally avoided all of the TAF sites. Despite that, there is still copious moisture across the area and the whole area is basically sitting within rain cooled air. The boundary will slowly shift southward tonight, maybe sparking a few showers closer to Columbia and CUB as it moves out of the upstate. Think this threat is low enough to keep it out of the TAFs at this point. The real threat to aviation tonight appears to be the development of ceiling or visibility restrictions later tonight. Weak subsidence aloft is expected to act on a moisture rich boundary layer and likely yield low ceilings. Vis restrictions are tougher to pin down. The sites that are more prone to fog in regular conditions are more likely to see fog with the stratus but the stratus should be more predominant at all sites regardless. Expecting this to persist through about late morning, with clouds clearing by early afternoon Saturday. Westerly and southwesterly winds are expected on Saturday.

EXTENDED AVIATION OUTLOOK...Thunderstorm chances remain into the weekend, with scattered to widespread convection expected.

CAE WATCHES/WARNINGS/ADVISORIES

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