textproduct: Columbia

WHAT HAS CHANGED

An isolated shower or storm is possible this evening, but expect mostly dry conditions into Friday morning. The remainder of the forecast remains on track for widespread convection Friday afternoon with flash flooding and damaging winds possible. Aviation Discussion updated for 00z TAFs.

KEY MESSAGES

- 1. Severe weather and flash flooding possible Friday.

- 2. An isolated shower or storm possible this evening.

DISCUSSION

KEY MESSAGE 1: Severe weather and flash flooding possible Friday.

The forecast for Friday largely remains on track as troughing over the eastern CONUS strengthens with another shortwave gradually working toward the region. Along with this upper support, a surface front is also expected to shift into the region through the day. Robust heating is expected through the morning into the afternoon with surface dewpoints in the low to mid 70s. This should quickly bring MLCAPE values near 2500-3000 J/kg with steep low level lapse rates bringing DCAPE values near 800-1000 J/kg. Enhanced kinematics with surging PWAT's to near 2" will bring the risk for wet microbursts in convection during the early afternoon. While damaging wind gusts are the primary threat, cannot rule out some hail as fairly thick CAPE profiles are seen in the hail growth zone. This is further supported in analog soundings with multiple analogs for near severe hail when pulling forecast soundings from the RAP/HRRR/RRFS. 12z guidance indicates convection could get going as early as 16- 19z, quickly expanding in coverage through the afternoon and into the early evening.

The overall storm motion is expected to be fairly slow (under 20 kts) and the environment appears primed for heavy rainfall with deep warm cloud depths, nearly boundary parallel deep layer shear vectors, and PWAT's near 2". The recent REFS and HREF PMM QPF amounts show spots of 2-4" near portions of the Pee Dee and northern Midlands, which is reasonable, but both of these ensembles are keying in on amounts near 3-6" just across the CWA border in southern NC. Any southern shift in forcing/ this axis of higher QPF could bring the higher amounts in the Pee Dee and northern FA. Overall, some uncertainty remains in the exact placement of the heaviest rainfall, but isolated to scattered instances of flash flooding will be possible mainly along and east of the I-26 corridor.

KEY MESSAGE 2: An isolated shower or storm possible this evening.

Convection kicked off a bit earlier than expected with a couple strong to severe storms this afternoon that generally helped to stabilize conditions. A few storms have quickly fired both north and south of the forecast area in the last hour or so as a result of some remnant outflow boundaries. While precip should be mainly done for the night, given the latest trends an isolated strong storm could remain possible into late this evening.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

VFR conditions expected through Friday morning, with restrictions expected in convection Friday afternoon and evening.

The convection from earlier this afternoon has been replaced by mostly clear skies. GOES PW imagery suggests that slightly drier air has overspread the area, making another round of convection seem somewhat unlikely this evening. This is supported by a lull in upper support that is expected to increase rapidly on Friday. Moisture is forecast to return in a hurry ahead of an approaching surface low and trough on Friday morning. Southerly and southeasterly flow will continue to push higher PW air in place as a surface low develops overhead. Convection is expected to begin early again - likely around 15z or 16z. Added a predominant VCTS to the TAFs with a long prob30 for TSRA from 16z to 22z. While this is an escalation from the previous forecast, it is likely that a predominant TSRA group will be needed with the 06z or 12z issuance as convection looks widespread for much of the afternoon tomorrow. Expect visibility restrictions & strong wind gusts as the primary aviation problems, with ceilings likely dependent on persistence of widespread, heavy rainfall into the evening hours.

EXTENDED AVIATION OUTLOOK...Thunderstorm chances remain into the weekend, with scattered to widespread convection expected.

CAE WATCHES/WARNINGS/ADVISORIES

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