textproduct: Columbia

WHAT HAS CHANGED

Increased heavy rainfall threat with today's activity. Aviation discussion updated for 12z TAF.

KEY MESSAGES

- 1. Scattered to widespread showers and storms expected this afternoon, continuing into the early overnight. A couple strong to marginally severe storms will be possible along with isolated spots of flash flooding. Lingering moisture leading to scattered to widespread afternoon storms Tuesday and Wednesday.

DISCUSSION

Key Message 1: Scattered to widespread showers and storms expected this afternoon, continuing into the early overnight. A couple strong to marginally severe storms will be possible along with isolated spots of flash flooding. Lingering moisture leading to scattered to widespread afternoon storms Tuesday and Wednesday.

Overall, there has not been much change in the outlook for today. A slow moving surface front should gradually work south through the FA before stalling near the CSRA as a mid-level low works into northern AL/GA. Mean sfc-400mb flow out of the southwest should advect PWAT's 1.5-2 standard deviations above normal (~2.20-2.40"), creating very moist profiles. With surface dewpoints remaining in the low to mid 70s, mean HREF soundings indicate SBCAPE values between 1500-2000 J/kg should develop through the day, less than previous days mostly due to cooler surface temperatures ranging from the low 80s north to the mid to upper 80s south. With more moist adiabatic profiles, DCAPE is progged to be less than previous day's as well. An uptick in kinematics from the mid level low should bring increased shear (EBWD ~20-25 kts) though, so a few strong to marginally severe storms remain possible during the afternoon/early evening with the main hazard being damaging wind gusts from precip- loaded downdrafts. Activity likely carries into the overnight, but the severe risk is expected to diminish during this period.

The bigger talking point is the heavy rainfall potential through the day. As 00z guidance has filtered in, there is an increased signal for locally high rainfall amounts. These moist adiabatic profiles, long/skinny CAPE, a nearly stationary front, and the aforementioned PWAT's should act to bring quite efficient rainfall rates and the potential for training convection. The HREF 24hr QPF LPMM product indicates a fairly widespread 0.50-1.0" is a reasonable expectation, but it does indicate spots of 2-5" being possible, which is further supported in deterministic CAMs and the 00z REFS LPMM. There is lesser confidence in the exact placement of higher QPF amounts with some spatial variability amongst deterministic CAMs, but with the frontal boundary expected to nearly stall in the southern FA, this could be an area to watch more closely. Areas in the southeastern Midlands near eastern Bamberg County into Orangeburg and southern Calhoun Counties saw 1-3" of rainfall from Sunday's activity so these spots would be the most sensitive to additional higher amounts. Overall, isolated instances of flash flooding will be possible if these higher amounts are realized.

Scattered shower and thunderstorm chances will likely continue Tuesday and Wednesday as ensemble meteograms indicate PWAT's near to over 2" remain in place through at least the first half of Wednesday. As the mid level low slowly retrogrades, drier air may begin pushing into the Pee Dee and northern Midlands Wednesday, bringing lower rain chances here. Cooler than normal temperatures are also expected to persist through Wednesday before gradually warming during the second half of the week back to near normal. Typical diurnal rain chances could make an appearance late in the week into next weekend, but there is generous spread in LREF cluster analysis at this point.

AVIATION /10Z MONDAY THROUGH FRIDAY/

Low Ceilings Possible This Morning....

At daybreak, MVFR ceilings are being reported at CAE/CUB, with LIFR ceilings at OGB. Guidance has backed off on the threat for low ceilings at the remaining terminals so opted to move the potential into a TEMPO and amend as needed. Any low stratus should lift and scour out by midday, giving way to scattered cumulus. Another round of afternoon and evening convection is expected, potentially resulting in brief restrictions at the terminals. PROB30 remains in place from 18z to 00z Tuesday for this potential. Confidence in MVFR-IFR ceilings appears to be higher Monday night once the convection dissipates therefore new lines were added to this update to reflect decreasing cloud bases.

EXTENDED AVIATION OUTLOOK...A good chance for afternoon showers and thunderstorms with associated restrictions is expected through at least Tuesday.

CAE WATCHES/WARNINGS/ADVISORIES

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