textproduct: Columbia

WHAT HAS CHANGED

Guidance has trended toward slightly lower rainfall totals through Saturday, along with a slower progression of the front. Aviation discussion updated for 18Z Update.

KEY MESSAGES

- 1. Rain chances increase as a slow-moving front approaches. Unsettled weather continues for the remainder of the week.

DISCUSSION

Key Message 1: Rain chances increase as a slow-moving front approaches. Unsettled weather continues for the remainder of the week.

The anticipated cold front will continue to slowly sag southward, eventually stalling near or over the FA. A modest moisture fetch from TS Bertha well to our SW will help advect tropical moisture to the region. Overall, this slow-moving pattern will be in place through at least Saturday.

PWATs are currently over 2" amid deep southwest flow, with relatively skinny CAPE profiles, and deep warm cloud depths. Mean flow will remain nearly parallel to the front, favoring training convection and highly efficient rainfall production. Hi-res guidance depicts more organized showers and clusters of thunderstorms developing later this evening and overnight, primarily across the northern Midlands. Locally heavy rainfall rates within these bands could quickly boost storm-total amounts. Scattered showers are expected to continue through Friday before another more organized round of storms develops during the afternoon and evening, with the greatest coverage shifting south toward the central/eastern Midlands and CSRA.

Given the expected convective evolution and tropical environment, rainfall totals are likely to vary considerably over relatively short distances. The 3 day rainfall forecast focuses the highest amounts in the northern Midlands and Pee Dee region (likely today into tonight). Further south, the rainfall is expected to be more intermittent with lower amounts. Repeated rounds of heavy rainfall will increase the potential for localized flooding.

Showers and thunderstorms will remain possible into Saturday, although coverage should become more scattered as the front weakens and eventually dissipates. Increased cloud cover and rainfall should provide some relief from the heat, especially across northern areas with afternoon highs generally in the lower 90s and potentially remaining in the upper 80s where rainfall occurs. A more typical late-July pattern is expected to return by next week, bringing back hot and humid conditions with diurnal thunderstorms.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

VFR likely into this evening with convection mainly staying north of the TAF sites. Increasing chances of restrictions tonight with MVFR/IFR cigs late tonight and periods of rain moving in.

A blanket of higher clouds has been over the region today helping to keep the atmosphere more stable and resulting in less cumulus than this time yesterday. Expect VFR cumulus clouds this afternoon but higher clouds persist throughout the forecast period. Most of the rain has remain well north of the terminals and expected to remain so until after 21-22z when some convection may move into the CAE/CUB area through late evening as the front to our north slowly sinks southward. Guidance has been backing off on restrictions, at least pushing them back later tonight with MVFR/IFR cigs arriving at CAE/CUB after 07z or so. Included prevailing MVFR cigs with a tempo to IFR cigs here 09z-13z. Lower confidence at the other terminals so only including a tempo for MVFR cigs at this time in the 09z-13z time frame. Some lingering showers may persist through the night into Friday morning at CAE/CUB with chances increasing all terminals toward the end of the forecast period with diurnal heating and the boundary in the area providing a focus for convergence.

EXTENDED AVIATION OUTLOOK...Periodic restrictions from showers and thunderstorms likely into the weekend for all TAF sites.

CAE WATCHES/WARNINGS/ADVISORIES

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