textproduct: Columbia

WHAT HAS CHANGED

Updated Key Message 1 to reflect latest mesoanalysis and guidance. Aviation discussion updated for 00z TAFs.

KEY MESSAGES

- 1. Warm and humid with scattered to numerous showers and thunderstorms this afternoon and evening.

- 2. Cooler conditions expected Wednesday onward, with periods of showers mainly Wednesday and Thursday.

DISCUSSION

KEY MESSAGE 1: Warm and humid with scattered to numerous showers and thunderstorms this afternoon and evening.

Midday convection has started to diminish across the central Midlands this evening with some showers still hanging around north of I-20, closer to the NC border. Latest mesoanalysis shows CAPE values have diminished across much of the area with higher values to our west closer to the front. PWATs still remain in the 1.8-2" range with efficient low-topped convection and rain rates in the 2-3" per hour range. A few storms have also started to develop in the upstate where instability remains elevated. Latest CAMs show convection should diminish here over the next few hours as we lose daytime heating. However, any storms/showers this evening could bring gusty winds and heavy rainfall. A localized flash flooding threat remains the main threat.

KEY MESSAGE 2: Cooler conditions expected Wednesday onward, with periods of showers mainly Wednesday and Thursday.

Models are generally converging on high pressure over the northeast pushing the wedge front through our forecast area late tonight into Wednesday. The ongoing showers and cloud cover Wednesday morning will likely limit daytime heating, especially with cold advection occurring at the surface. There remains some uncertainty regarding how far south the wedge front will go, and it is expected to have a tight temperature gradient setting up somewhere across the southern Midlands Wednesday afternoon. All said, the temperature drop of 10 to 15+ degrees between Tuesday and Wednesday will be very noticeable north of the front. There will also be some breezy northeast winds accompanying this airmass change. Blended guidance struggles in these scenarios, so we have been using the NAM/GFS models to better capture the expected temperatures late this week.

Additional cloud cover and precip suggests Thursday could be our coolest day of the week for high temperatures, with most expected to remain in the low to upper 70s. An upper trough will work to scour out the wedge through some portion of the day, with drier Northwest flow eventually moving in. Highs will rebound a bit closer to normal as precip and cloud free conditions return Friday and into this weekend. Highs will generally reach the upper 70s to low 80s, with overnight lows in the upper 50s to low 60s. Overall, this should provide our first real taste of fall with a refreshing change in temperatures arriving just as astronomical autumn officially begins later today!

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

Widely scattered showers and storms possible overnight as a cold front pushes in the from the north along with widespread restrictions.

Although convective activity will be lower overnight we expect at least isolated to widely scattered storms to continue into the late evening with continued showers or light rain into the morning as the cold front pushes south into the forecast area. This front will set up wedge conditions over the region with widespread ceiling restrictions and a shift to northerly winds by 03Z-09Z. Some uncertainty remains regarding how far south the wedge will settle in by Wednesday morning, but IFR ceilings are likely and will continue through the morning and possibly the remainder of the day. There is some possibility of some improvement at AGS, DNL and OGB late morning but it would be short lived as the front continues south and ceilings lower.

EXTENDED AVIATION OUTLOOK...Widespread restrictions continue Thursday as wedge conditions remain over the region with showers likely. Drier conditions expected beginning Friday but low ceilings may persist longer than model guidance suggests.

CAE WATCHES/WARNINGS/ADVISORIES

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