textproduct: Columbia

WHAT HAS CHANGED

Risk for a strong storm or two today has increased. Forecast remains on track for widespread convection Friday with flash flooding and damaging winds possible. Aviation Discussion updated for 18z TAF.

KEY MESSAGES

- 1. Severe weather and flash flooding possible Friday.

- 2. A couple strong to severe storms possible this afternoon.

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: A couple strong to severe storms possible this afternoon.

Convection is already firing this afternoon, likely in reaction to a convectively enhanced shortwave moving into the region from the Appalachians. Earlier this morning convection in southern Tennessee produced an undular bore/gravity waves that were sampled by the KFFC/KHTX radar and on satellite imagery. It is less evident now, but these waves may be persisting as the shortwave moves overhead. With a strongly unstable environment (SBCAPE over 3000 J/kg), PWAT's near 1.6-1.8", and deeply mixed low levels, strong to damaging downburst winds will be possible in the strongest storms, with multiple already being observed as of writing this. The quick moving shortwave is already shifting eastward, so I would not be surprised if coverage actually decreased some in the coming hours, but an isolated strong storm could remain possible into the early evening hours.

AVIATION /19Z THURSDAY THROUGH TUESDAY/

Mainly VFR conditions expected to persist outside of possible convection.

Regional visible satellite along with radar composite showing much of the forecast area area the taf locations are beginning to get active this afternoon with showers and thunderstorms. Based on that, all sites will be starting off with vcts, along with a tempo group through 22z to account for mvfr visibilities and gusty winds with any activity that impacts the tafs. Outside of this convection, vfr conditions should prevail through the period. Additional showers and storms will be possible again Friday afternoon, with potential for greater coverage and stronger storms with heavy rainfall. Have handled with prob30 for now that far out.

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

CAE WATCHES/WARNINGS/ADVISORIES

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