textproduct: Columbia

WHAT HAS CHANGED

Possibility for localized flash flooding this evening into early Sunday. Timing has shifted a bit later for more widespread rain Sunday. Aviation discussion updated for 18z TAFs.

KEY MESSAGES

- 1. Front approaching the area leading to increasing chances for rain and cooler temps this weekend and into next week. Increased concern for localized flash flooding.

DISCUSSION

KEY MESSAGE 1: Front approaching the area leading to increasing chances for rain and cooler temps this weekend and into next week. Increased concern for localized flash flooding.

Rest of Today into Sunday Morning: Deep southwesterly flow is bringing robust moisture advection across the region as PWAT's are reaching between 2-2.25". The advertised surface front is gradually drifting southward from NC, currently nearing the Upstate and southern NC. As of writing this, widely scattered showers are seen across SC, with the main focus at the moment being just north of the CWA. Widespread cloud cover has limited instability but brief pockets of clearing are being seen toward the southeastern Midlands and along I-20. This should lead to weak, but sufficient (considering the moisture content) instability for isolated to scattered storms the remainder of the afternoon and into this evening. High-res guidance as a whole has done pretty poor with handling current conditions, but runs from the 12z HRRR onward have been doing a bit better, displaying this gradual increase in coverage. Enhanced convergence along the front is expected this evening and tonight, bringing a batch of convection into the northern Midlands and Pee Dee region. The HRRR continues to hint that this area north of I-20 could become a focus for slow moving (potentially back-building) convection tonight where deep warm cloud layers, boundary parallel shear/flow, and moisture near the climatological 99th percentile should yield very efficient rainfall. Given low CAM consensus, confidence remains a bit low, but this solution from the HRRR is a reasonable worst-case scenario, where a swath of 3"+ of rainfall could be possible into Sunday morning. Due to this, localized flash flooding could be possible this evening into Sunday morning, mainly north of I-20 toward the northern Midlands and the Pee Dee.

Sunday into early Monday: There has not been a significant change in the outlook for Sunday as the weak front is expected to stall and meander through the FA, but upper support should increase through the day as a shortwave moves in. PWAT's are expected to remain near 2.25" and the overall thermodynamic, and kinematic profiles should not be all too different from today. The main shift in guidance is toward a later timing of the onset of widespread rain/storms with a slower moving shortwave. This timing favors late Sunday afternoon through early Monday for the window of opportunity for widespread moderate to heavy rain. Overall, this environment is expected to remain conducive for instances of flash flooding, especially for any areas that see heavy rainfall tonight. The 12z HREF and REFS continue to disagree on the exact placement of a corridor of higher rainfall amounts, but the overall trend has been a bit further south, mainly along and south of the I-20 corridor, where the front could stall. In this swath, LPMM products from both high-res ensembles show amounts between 2-5". Trends of frontal placement will continue to be monitored, but all-in-all, fairly widespread rainfall is expected into early Monday, and due to the efficient nature of the rainfall and the potential for training, WPC has maintained their Slight Risk (level 2 out of 4) for excessive rainfall across the CWA.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Mostly VFR today with scattered showers and isolated storms. Restrictions increasing tonight into Sunday morning.

Scattered showers visible on radar and may impact the terminals briefly this afternoon, although forcing is weak, limiting convective coverage. While isolated storms may impact the Columbia terminals over the next several hours, the rest of the terminals will likely just deal with showers. Tonight a front will move into the area from the north with increased chances for moderate to heavy rain along the front which may lead to decreasing visibilities. More notable restrictions will be lowering ceilings with high confidence in IFR ceilings, especially for the northern terminals into tomorrow as precipitation induced CAD develops. As a result, expect restrictions to continue through 18z tomorrow.

EXTENDED AVIATION OUTLOOK...Scattered to widespread showers and isolated thunderstorms Sunday night into Monday morning likely lead to restrictions. Drier air filtering in Monday.

CAE WATCHES/WARNINGS/ADVISORIES

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