textproduct: Columbia

WHAT HAS CHANGED

Decreasing confidence in severe storms this afternoon into evening. Updated aviation discussion for 18z TAFs.

KEY MESSAGES

- 1. 1. Scattered showers and thunderstorms this afternoon and then a better chance of more widespread rain late tonight into Thursday morning.

- 2. Confidence increasing in moderate rainfall for portions of the forecast area Friday night and Saturday.

DISCUSSION

Key Message 1: Scattered showers and thunderstorms this afternoon and then a better chance of more widespread rain late tonight into Thursday morning.

Morning convection associated with southeastward moving MCV has shifted south of the area and shifting off the coast early this afternoon. Satellite imagery showing a mix of clouds and sun across the forecast area with the stratocumulus clouds transitioning to cumulus as temperatures are rising through the 70s with dewpoints remaining in the 60s. Latest hi-res guidance showing isolated/scattered convection developing this afternoon into evening ahead of an approaching frontal boundary. Mesoanalysis currently showing a relatively stable air mass from earlier rain and clouds but with several hours of potential sunshine sufficient instability may be realized to support the isolated convection with the possibility of a strong storm or two. Severe convection, while possible, does not seem as likely.

The frontal boundary should move through the region overnight and there could be scattered convection along it as it moves through but given the timing being overnight with limited instability, again do not anticipate much of a severe threat with it. Guidance is continuing to highlight another convective complex developing across the lower MS Valley and Gulf Coast states which should move over the forecast area late tonight into Thursday morning bringing another chance of showers and possible thunderstorms. The CSRA seems to be more favored than further to the north and highest pops reside generally along and south of the I-20 corridor. Instability looks to be more elevated in nature but there will be shortwave energy providing upper support as it moves through. Any rainfall at this point will continue to be beneficial given our drought conditions.

Key Message 2: Confidence increasing in moderate rainfall for portions of the forecast area Friday night and Saturday.

Chances of the most significant rainfall we have seen in a while continue to look pretty good for Friday night into Saturday. Northern stream energy digging into the upper Midwest is expected to phase with southern stream energy moving across the southern Plains into the MS Valley on Friday before swinging through the Carolinas and off the Mid-Atlantic coast Saturday night. This will induce low pressure development along the Gulf Coast which then lifts northeastward off the Carolina coast on Saturday. While it appears the heaviest rainfall and highest totals likely remain south of our area, there should be reasonable chances for much needed rainfall with NAEFS IVT above the 97th percentile. The CSRA and southeast Midlands are more favored for highest rainfall given a gradient in PWATs with higher values from north to south. There is little instability available with this system as it looks like an overrunning event with the surface low to our southeast. LREF Probabilities for 24hr rainfall amounts greater than 0.5 inches are in the 50-75 percent range for Friday night through Saturday and probabilities of greater than 1 inch are near 50 percent in the southeast Midlands. 48hr QPF from the NBM is a bit more bullish with precipitation with the 50th percentile showing much of the forecast area receiving at least one inch of rainfall.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Generally VFR conditions this afternoon expected with increasing shower chances early Thursday.

Lingering low stratus continue to burn off this afternoon with typical strato-cu developing across the area. A weak approaching front will likely develop a few isolated showers and thunderstorms later this afternoon across northern SC, but confidence is too low for any terminal impacts beyond a VCSH at CAE and CUB. More widespread showers and possibly thunderstorms are expected early Thursday morning after 06z from a decaying storm complex to our west. Showers and associated restrictions are more likely for OGB, AIK and the Augusta terminals so included a tempo there and a prob30 for the Columbia area terminals. Some brief gusty winds are possible with these showers-storms but generally should remain elevated. Some lingering stratus will continue into Thursday afternoon following these showers- storms.

EXTENDED AVIATION OUTLOOK...Periods of restrictions are possible late this week into the weekend with more rain chances, especially Friday night and throughout Saturday.

CAE WATCHES/WARNINGS/ADVISORIES

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