textproduct: Columbia

WHAT HAS CHANGED

Forecast remains on track for possible severe thunderstorms today bringing the risk of damaging wind gusts, small hail, and localized flash flooding. Aviation discussion updated for 18z TAF issuance.

KEY MESSAGES

- 1. Damaging winds, localized flash flooding possible today.

DISCUSSION

KEY MESSAGE 1. Damaging winds, localized flash flooding possible today.

Multiple rounds of showers and thunderstorms are expected to traverse the Southeast today as shortwaves move through the broader trough. Convection over the southern Appalachians will work towards the forecast area mid day and early afternoon. The most prominent shortwave is expected to push into the area later in the day enhancing convective development and supporting thunderstorms into the evening, especially in the southern forecast area where instability will be greater.

A weak surface boundary is slowly moving into the forecast area from the north. Convergence along the boundary will trigger convection this afternoon and evening. Damaging wind gusts are the primary threat with large hail also possible. mlCAPE values are progged from 1500 to 2000 J/kg this afternoon with forecast soundings showing an inverted-V signature indicative of a downburst wind threat. With PWAT values higher than the previous day DCAPE values are not quite as high as yesterday, peaking near 1000 J/kg, but still supportive of damaging downburst winds. With PWAT values near 2 inches across the area this would point to an increased risk of heavy rainfall and localized flash flooding. The main area of concern will be urban areas and the few localized spots which received heavy rainfall the previous day.

For the remainder of the forecast, global ensembles favor broad ridging developing over much of the CONUS next week. With easterly, onshore flow for the first part of the week and deeper SW flow for the latter part, we will likely see PWAT values near or slightly above normal. This pattern supports isolated to scattered showers and thunderstorms most days next week with temperatures near or above normal after Monday.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

Another round of diurnal convection late afternoon/evening expected then restrictions associated with stratus and fog late tonight.

Scattered cirrus with a few areas of 4 kft cumulus have developed over the area this afternoon, with generally light northeasterly winds of 5-6 kts. Similar to yesterday, showers and thunderstorms are expected to develop late afternoon and into this evening as a cold front sinks southward. A few storms could bring gusty winds and temporary restrictions over terminals. Given the uncertainty in timing and coverage, PROB30 groups have been maintained at all sites from 21-03z. Confidence remains low regarding how long convection will persist into the night with some short-range guidance suggestion coverage could continue into the early morning hours Monday.

Lingering debris clouds from convection should gradually clear out as low clouds and fog are expected to develop tonight. MVFR/IFR cigs are possible at the terminals between 06-15z Monday, with the strongest confidence to our southern and eastern terminals. Conditions should gradually improve by midday as ceilings lift with SCT cumulus bases around 3-5 kft. Winds will increase to 6-9 kt generally from the NE.

EXTENDED AVIATION OUTLOOK...Diurnal storm chances continue into the first half of the week.

CAE WATCHES/WARNINGS/ADVISORIES

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