textproduct: Columbia

WHAT HAS CHANGED

A severe thunderstorm watch has been issued for the entire CWA until 9 PM EDT. Thunderstorms will develop this afternoon and could produce damaging winds and localized flash flooding. 18z Aviation.

KEY MESSAGES

- 1. Severe weather and flash flooding possible today.

DISCUSSION

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

The frontal boundary draped from the Southern Plains into the Southeast will continue to interact with the unstable, warm airmass across the FA. GOES-E water vapor imagery shows a convectively enhanced shortwave at the base of the larger trough, with a positively tilted trough extending back into central GA. Following some morning convection across the southeast portion of the FA, storms are starting to redevelop and continue into this evening along the weak stationary front and interaction with the sea breeze/storm outflows.

Moisture advection and daytime heating have allowed MLCAPE values to increase to around 1500-2000 J/kg and DCAPE values around 1000-1200 J/kg, with pockets of greater instability possible. PWAT values near 2 inches, steep low-level lapse rates, and weak divergence aloft will support an increased risk for thunderstorms capable of producing wet microbursts. Deep- layer shear remains weak, which should should help limit widespread storm organization, however, some storms could become severe with heavy rainfall and downburst winds dominating. There is also potential for training cells to develop along the west-east-oriented boundary to our north. This area will be of greatest concern for flash flooding, although urban areas and locations that are typically prone to flooding will also need to be monitored closely. CAM guidance has continued to struggle with the timing and initiation of convection, but overall activity should gradually decrease after sunset.

An upper trough will dig in on Saturday, with the axis shifting farther east. This will allow direr air to begin moving into the western portion of our FA this weekend. However, deeper moisture and moderate conditional instability along the coast could support another threat along the coast for microbursts and damaging winds in the afternoon, particularly near the I-95 corridor. Beyond that, a more seasonal pattern is expected to develop, with temperatures closer to normal, increasing humidity, and daily chances for isolated to scattered showers and thunderstorms.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Two periods of restrictions expected this period. First potential will be in convection this afternoon and evening. Second period of seeing restrictions will be after 06z through 15z.

Regional radars showing convection already developing and/or ongoing across the region. Vfr conditions should prevail outside of any convection this afternoon and evening, with periods of mvfr/ifr visibilities in heavy rain with the storms. Additional restrictions are now being shown late tonight and into Saturday morning, with increasing potential of ifr/lifr between 06-15z. Guidance is showing the development of low ifr stratus after 06z, with some period with mvfr visibilities at all locations. Only have moderate confidence in that right now, but have gone ahead and included restrictions overnight at all sites. Some improvement to mvfr should occur by 15z, with possible vfr near the tail end of the current taf period.

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

CAE WATCHES/WARNINGS/ADVISORIES

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