textproduct: Columbia

WHAT HAS CHANGED

Heaviest rain threat for tonight continues to shift slightly westward. Aviation discussion updated for 18z TAF issuance.

KEY MESSAGES

- 1. Shower and thunderstorms this afternoon, mainly in the CSRA, then expanding over the area into Saturday.

- 2. After a cold front Sunday, pattern becomes more uncertain.

DISCUSSION

Key Message 1: Shower and thunderstorms this afternoon, mainly in the CSRA, then expanding over the area into Saturday.

A few showers/storms have begun to develop along a weak boundary extending from the coast into Burke County. The main frontal boundary is currently draped to our southwest, generally from the Atlanta area southeastward to Jacksonville. The highest moisture is also pooling around this boundary, where PWATs are at 2" or above. Moisture drops quickly northeastward of this boundary with areas along the SC/NC border seeing PWAT values of an inch or slightly below as of this update. So, thinking most of the activity remains to our southwest through the next few hours.

The aforementioned boundary is forecast to inch northeastward through the late afternoon into tonight, bringing increased precipitation chances along with it. Latest hi-res guidance suggests that the 2" PWATs gradually diminish as the boundary approaches the area tonight. As such, the HREF, along with deterministic hi-res models, keep the heaviest rain just to the southwest of the CSRA and tapers it off as it moves into the area tonight. Regardless, locally heavy rain, with limited potential for isolated flash flooding remaining possible as we head into tonight/early Saturday morning. Rain is then expected to spread across the forecast area through the day tomorrow morning before diminishing in the afternoon.

Key Message 2: After a cold front Sunday, pattern becomes more uncertain.

An upper trough digging south along the eastern seaboard is expected to send a cold front through the forecast area Sunday, bringing additional rain chances along with cooler and drier air to the area to end the weekend. After this frontal passage, the forecast guidance starts to show uncertainty as solution

Beyond Saturday, the forecast becomes a bit trickier. Most guidance suggests a brief drying trend Sunday, followed by another round of rainfall Monday ahead of a stronger cold front. That system is expected to track off the East Coast through midweek, allowing cooler and drier high pressure to build in from the north. However, guidance remains a bit uncertain beyond that. There seems to be decent agreement in another front moving through midweek, but then the models really diverge after that.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

A mixture of mvfr/vfr through this afternoon, then a return to mvfr/ifr restrictions late tonight and for much of Saturday.

Surface front is stalled outside of the forecast area this afternoon. North of the front, a mixture of mvfr/vfr broken cumulus exists, and although ceilings should be rising back to vfr by 19z, can not rule out brief mvfr this afternoon at any site. The surface front will be pushing back to the north overnight and into Saturday. This will bring moisture back into the forecast area, along with increasing rain chances. Best rain chances this evening and early tonight should remain confined to the CSRA region, with ags/dnl/aik showing the most potential for some light rain formation prior to 00z. Additional coverage then expected through sunrise on Saturday as moisture deepens across the region. Towards morning rain chances should increase towards the Midlands, but only included prop30 for cae/cub/ogb at this time due to some model inconsistencies with coverage and timing. Ceilings as the front moves north are expected to begin dropping back into mvfr after midnight at all locations, with those conditions then prevailing through the daytime on Saturday. Winds this afternoon turning more southeasterly, then light and variable overnight and Saturday.

EXTENDED AVIATION OUTLOOK...Unsettled weather should continue into early next week until drier air moves into the region mid-week.

CAE WATCHES/WARNINGS/ADVISORIES

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