textproduct: Columbia

WHAT HAS CHANGED

The area for the greatest threat of severe weather today is trending slightly further south. Aviation discussion updated for 18z TAFs.

KEY MESSAGES

- 1. Periods of heavy rain, gusty winds through this evening

- 2. A brief tornado is possible in the far southern forecast area

- 3. Dry, warm weather favored for next week

DISCUSSION

Key Message 1: Periods of heavy rain, gusty winds through this evening

We will continue to see light to moderate showers over the next few hours. Although they may cause some nuisance ponding of water along roadways, we do not expect them to cause significant impacts.

The greatest chance for heavy rainfall will be this afternoon (after 2 PM) and into the evening as a surface boundary shifts northward into the southern Forecast Area (FA) and heavier showers or thunderstorms develop along the boundary. Periods of heavy rain with isolated amounts around 3 inches will be possible and may lead to flash flooding. HREF PMM and WoFS 90th percentile show isolated values in the 2 to 4 inch range with maximum values from individual CAMs still generally under 4 inches. The location of the heavier rainfall should be tied to the surface boundary which will continue to lift north into the evening. This will mean that the potential for flash flooding will mainly be south of I-20 and persist through 9 PM or so. The threat of flooding will diminish overnight as convection weakens and the heaviest rain exits the forecast area.

A Wind Advisory remains in effect until 11 PM. It will be breezy across much of the area, with gusts of 25-35 mph possible. Outside of thunderstorms, winds will diminish through the late afternoon and evening.

Key Message 2: A brief tornado is possible in the far southern forecast area

The main feature of interest today will be a surface boundary currently located to our south. This boundary is progged to push north through the afternoon and evening bringing a conditionally unstable air mass up into the southern FA. WoFS and HRRR model trends this morning have tended to keep the boundary further south with only the southern-most portions of our southern tier of counties within the warm sector. This slower and more limited progression will limit the overall threat of tornadoes this afternoon as the stronger wind fields slowly pull away from the area. The high shear and SRH values currently over the region will lower as we continue through the afternoon. That said, effective SRH values from 100 to 200 m2/s2 could still be sufficient for a brief, weak tornado along the surface boundary as it lifts northward this afternoon. The stable air mass may first break in the extreme southern FA around 2 PM which would mark the beginning of the potential tornado threat. Warm advection through the evening will keep the threat in place longer than what would be expected from a typical diurnal trend. Models generally agree that storms will weaken by 11 PM this evening.

Key Message 3: Dry, warm weather favored for next week

Global ensembles are in good agreement that upper level ridging will build over the Deep South for most of next week. PWAT values below 1.5 inches and NAEFS 500 mb heights at or above the 90th percentile for the time of year supports dry weather with rising temperatures through the first part of the week. Highs will likely be in the mid to upper 80s for the middle of the week (Tue - Thu); approaching record highs.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Widespread restrictions are expected to continue into Sunday morning before gradually improving.

Widespread IFR ceilings continue this afternoon as scattered to widespread rain moves through with periods of visibility restrictions. Gusts have eased off some, but winds generally remain out of the northeast to east around 10-12 kts. Rain showers likely continue through the afternoon and tonight, but a few thunderstorms could be possible, mainly near AGS/DNL/OGB. Confidence in impacts from these is too low at the moment for anything beyond a PROB30 group. Tonight, winds lighten a bit toward 5-10 kts, turning more southeasterly to southerly as IFR to LIFR ceilings continue with rain showers. Rain should gradually come to an end between 10-15z Sunday with ceilings that gradually lift, though MVFR ceilings are expected to continue through the end of the TAF period. Winds become more southwesterly to westerly late in the period where additional gusts toward 20 kts could be possible heading into Sunday afternoon.

EXTENDED AVIATION OUTLOOK...Conditions continue to improve later on Sunday and into early next week.

CAE WATCHES/WARNINGS/ADVISORIES

SC...Wind Advisory until 11 PM EDT this evening for SCZ018-025. Flood Watch through Sunday morning for SCZ018-025-030-035-041- 135>137. Lake Wind Advisory until 11 PM EDT this evening for SCZ016- 020>022-026>031-035-037-038-041-115-116-135>137. GA...Wind Advisory until 11 PM EDT this evening for GAZ040-063>065- 077. Flood Watch through Sunday morning for GAZ040-063>065-077.