textproduct: Columbia

WHAT HAS CHANGED

Updated Key Message #1. Aviation discussion updated for 00z TAFs.

KEY MESSAGES

- 1. Isolated to widely scattered convection over the coming hours and again on Tuesday with hot/humid conditions continuing.

- 2. Rain chances increase Wednesday and remain high through the weekend. Severe weather will be possible on Wed and Thu.

DISCUSSION

Key Message 1: Isolated to widely scattered convection over the coming hours and again on Tuesday with hot/humid conditions continuing.

This Evening: A couple showers are seen in the CSRA and southeastern Midlands as MLCAPE values now sit around 2000 J/kg. Cannot rule out an isolated storm over the next 2-3 hours, but any activity is expected to remain fairly spotty and the risk for any strong storm is low. Dry conditions are then expected tonight.

Tuesday: As the gulf system drifts slightly westward, models project a dry slot of air advecting up into the forecast area during the day on Tuesday. PWAT values around 1.5 inches over much of the area should limit the extent of convective development. That said we could see a few isolated thunderstorms, particularly along the sea breeze Tuesday afternoon. The threats of severe weather and heavy rain are low. The drier air mass should also allow dewpoints to mix into the 60s reducing the chances of meeting Heat Advisory conditions despite highs mainly in the mid 90s.

Key Message 2: Rain chances increase Wednesday and remain high through the weekend. Severe weather will be possible on Wed and Thu.

The overall synoptic pattern remains unchanged in global ensembles for later this week and the weekend. A strong upper level trough will likely extend from the eastern Great Lakes down into the Mid-Atlantic. The associated cold front will dive down into the Mid-Atlantic and could near the FA Wednesday through Thursday. IVT values from the NAEFS ahead of the front are near the 90th to 99th percentile of climatology. There remains some uncertainty in the depth of the upper trough and how far south the front will push but on average the front is expected to get near enough to the FA to support widespread showers and thunderstorms late Wednesday and Thursday. Seasonable instability and moderate deep layer shear should support somewhat organized thunderstorms and possibly severe weather.

Global models depict the frontal boundary stalling near or over the FA on Thursday as a shortwave passes. Continued moisture advection into the region, and convergence along the front supports widespread thunderstorm chances with heavy rainfall possible. With the region remaining in northwest flow into the weekend, a series of shortwaves are expected to continue pushing through, enhancing convective development potentially outside of typical diurnal hours.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

VFR Conditions Expected Outside of Isolated Convection.

Several outflow boundaries from earlier convection have been pushing through the central Midlands and into the CSRA early this evening. These are currently on the dry side, but can not rule out an isolated shower until sunset. In addition, some shower activity possible as showers moving through eastern GA track northward towards the CSRA. Will handle CSRA with a tempo through 02z for mvfr visibilities in - tsra with vcsh also mentioned. May need to extend if the eastern GA activity holds together the next few hours as it moves northwards. Across the central Midlands, isolated shower/storm activity not entirely out of the question, but will hold off on mention at this time due to lower confidence. After 06z all sites will remain vfr, with a dry forecast overnight and into Tuesday. Winds will remain southerly between 5-10 kts through sunset, then drop to around 5 knots overnight. Stronger and gustier winds will take hold out of the south after 15z Tuesday, with gusts over 20 kts possible after 18z at all sites.

EXTENDED AVIATION OUTLOOK...Potential for restrictions from showers and thunderstorms continues with the threat increasing for the mid to late week period.

CAE WATCHES/WARNINGS/ADVISORIES

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