textproduct: Columbia

WHAT HAS CHANGED

Flash Flood Watch in effect starting at Noon today for the Columbia Metro Area and counties to the south and east. Key message updated to reflect latest model guidance. Aviation discussion updated for 12Z TAF Update.

KEY MESSAGES

- 1. Scattered to numerous showers and thunderstorms expected today, resulting in heavy rainfall and localized flash flooding. Rain persists into the Saturday, mainly across the eastern forecast area.

DISCUSSION

Key Message 1: Scattered to numerous showers and thunderstorms expected today-tonight, resulting in heavy rainfall and localized flash flooding. Rain persists into the Saturday, mainly across the eastern forecast area.

After many days of anticipation, the backdoor cold front has reached the forecast area and will continue to drift south towards the southern Midlands and CSRA. Now that the boundary has reached South Carolina, the threat for heavy rainfall and flash flooding will be highest today along the PWAT swath of 2.25-2.5". The WPC has placed the majority of the CWA in a Slight (2/4) risk for excessive rainfall with a Moderate (3/4) risk across the southeastern Midlands. The slow moving front will serve as an axis for rounds of showers and thunderstorms supported by rising PWATs in excess of 2", increasing low to mid level moisture- forcing, and decreasing winds-shear aloft. But 00z and 06z suites of model guidance are somewhat concerning, showing the potential for 2 to 4 inches of rainfall, with locally higher amounts in excess of 5 inches. HREF and REFS guidance suggest, like we have seen in NC, waves of on and off heavy showers- storms during daytime hours and then more persistent training showers overnight. So the primary flash flood threat may not fully materialize until overnight into Saturday. The main concern will be from urban and small stream flooding, especially if training thunderstorms move over areas prone to flash flooding. Regardless of whether you are in the watch itself, everyone should remain weather aware today and remember to turn around, don't drown should you encounter a flooded roadway.

Showers and thunderstorms will remain possible into Saturday, although coverage should become more scattered as the front weakens and eventually dissipates. Model guidance suggests that the eastern forecast area will be more likely to see significant rainfall on Saturday, especially along and east of I-95. The clouds and rain should provide some relief from the heat with forecast highs today mostly in the 80s and a few degrees warmer on Saturday. A more typical late July pattern is expected to return next week, bringing back hot and humid conditions with diurnally driven showers and thunderstorms.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Mix of restrictions expected throughout the TAF period with periodic lowering cigs and heavy rain-storms.

A slow moving front is draped across the area and will bring IFR cigs through the middle of Friday morning along with periodic showers to CAE and CUB; other sites should remain above IFR through the morning. Cigs will lift later this morning to MVFR across the area but waves of showers and thunderstorms remain expected until the end of the TAF period. Periodic IFR- LIFR restrictions likely at times along with thunder especially late this afternoon and overnight; including several groups of tempos and prob30's to try to convey this. Confidence is highest in notable restrictions at CAE, OGB, and CUB from 00z Saturday - 12z Saturday. Winds for CAE and CUB should remain out of the northwest throughout the period while OGB, DNL, and AGS will be slightly more variable closer to the front.

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

CAE WATCHES/WARNINGS/ADVISORIES

SC...Flood Watch from noon EDT today through late tonight for SCZ027-028-031-037-038-041-135>137. GA...None.