textproduct: Columbia

WHAT HAS CHANGED

Aviation discussion updated for 12z TAFs.

KEY MESSAGES

- 1. Isaias continues to move inland with widespread rain, tornado threat and gusty winds expected for our area into tonight.

DISCUSSION

Key Message 1: Isaias continues to move inland with widespread rain, tornado threat and gusty winds expected for our area into tonight.

As expected, PWATs have increased early this morning with a tight gradient over the area with PWATs greater than 2 inches to the south and increasing over the forecast area. While rainfall has moved into the area, it has remained light and in some spots to the north is not actually reaching the ground yet with 5 to 10 degree dew point depressions. Rain will likely be relatively light through much of the morning with isentropic lift leading to widespread rain with generally weak rain rates. As a warm front lifts northward through into the forecast area, hi resolution guidance continues to favor surface destabilization in the southern portion of the forecast area this afternoon. This generally favors more narrow banding of convective precip which guidance appears to be converging on, even the global models which were previously favoring a more broad brush approach. Still plenty of uncertainty as to the location of the heaviest rain bands so have expanded the Flood Watch to include more of the southern portion of the forecast area where highest confidence in moderate destabilization remains and potential for bands exceeding 3 inches and localized flash flooding. Warm advection into tonight ahead of a cold front associated with the post-tropical transition of Isaias will lead to lingering convection , although it should be moving at a fairly fast pace from southwest to northeast. Flood Watch has been extended through Saturday night, however, to account for any rainfall that falls in flood sensitive areas.

The tornado threat remains essentially unchanged with this cycle with nearly identical slight risk from SPC for the southern half of the forecast area. KCAE VAD Wind Profile already shows strong low level shear/SRH (sfc to 1 km shear 26 kts, sfc to 1 km SRH 268 m2s-2). While the area remains north of the front, as Isaias' circulation lifts northward, the aformentioned thermal gradient is expected to lift northward as well. The timing of this should be such that it occurs as the best moisture transport approaches behind the initial warm front, which could create a scenario on Saturday night that we see low-topped supercells develop in a highly sheared environment. LCLs will be quite low, and we typically don't need much more than a surface dewpoint of 70F to have some tropical tors develop. REFS and HREF members continue to favor sufficient destabilization for convection to develop in a very favorable shear environment. Will need to monitor developing storms Saturday afternoon into Saturday night. Have multiple ways to receive warnings on Saturday night!

Winds are the other threat but likely the least impactful. Some gusts over 40 mph are expected in the western Midlands and as a result, a wind advisory has been issued to cover this potential throughout Saturday. Otherwise, it should just be breezy across much of the area, with gusts of 25-35 mph possible especially Saturday morning and early afternoon.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

Widespread restrictions are expected through the TAF period.

Scattered light to moderate rain has overspread the region with a mix of IFR and MVFR ceilings and periods of reduced visibilities. Winds remain out of the northeast around 10-15 kts and gusts up to 25 kts will remain possible continuing through the morning and into the afternoon until around 18-21z. A few gusts up to 30 kts could be possible at the Augusta terminals. A frontal boundary is expected to lift northward through the day and this could shift winds to become more southeasterly by the evening. Scattered to widespread rain showers should continue much of the TAF period, though some thunderstorm development could be possible mainly after 18z, bring additional periods of visibility restrictions. Widespread IFR to MVFR ceilings should continue through the day and overnight, where periods LIFR stratus could be possible.

EXTENDED AVIATION OUTLOOK...Periods of rain continues into Sunday, leading to ongoing restrictions. Conditions begin improving later on Sunday and into early next week.

CAE WATCHES/WARNINGS/ADVISORIES

SC...Wind Advisory until 11 PM EDT this evening for SCZ018-025. Flood Watch through Sunday morning for SCZ018-025-030-035-041- 135>137. Lake Wind Advisory until 11 PM EDT this evening for SCZ016- 020>022-026>031-035-037-038-041-115-116-135>137. GA...Wind Advisory until 11 PM EDT this evening for GAZ040-063>065- 077. Flood Watch through Sunday morning for GAZ040-063>065-077.