textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

The forecast continues to trend wet and cool, especially through the Memorial Day holiday weekend.

The aviation discussion was updated to reflect the 00Z TAF issuance.

KEY MESSAGES

1. A cold front approaches the area tomorrow and then stalls through the weekend into early next week bringing a noticeably wetter and cooler forecast.

DISCUSSION

Key message 1: A cold front approaches the area tomorrow and then stalls through the weekend into early next week bringing a noticeably wetter and cooler forecast.

An upper low associated with a Tropical Upper Tropospheric Trough (TUTT) continues to spin just off the Carolina coast while upper ridging breaks down and gets shunted east and offshore. This is occurring as broad troughing becomes established from the Rockies through the Great Plains. This in turn places the southeast states with a moist southwest flow regime with multiple shortwaves and perturbations embedded within the background flow regime. A surface cold front is also dropping across the Ohio Valley and towards the Appalachians. Another warm summer-like day continues this afternoon with temperatures well into the upper 80s to low 90s. Isolated to widely scattered showers and a few thunderstorms will be possible mainly across the mountains later this afternoon through the evening. By tomorrow, the frontal boundary finally pushes into the area and will work in conjunction with peak heating to instigate much greater coverage of convection across much of the area. Convective initiation will occur late enough in the day that temperatures will still be warm, but a few degrees below today. Modest instability will be in place along with at least some flow through the column. CAMs do indicate the potential for a couple loosely organized multicell clusters and perhaps linear segments which could take advantage of the environment and produce locally gusty winds and perhaps an isolated damaging wind gust or two. Meager lapse rates and a lack of more downdraft CAPE will likely limit any severe threat, however.

The most noticeable changes will occur Friday into the weekend as a stout surface high migrates from the Great Lakes into New England. This will allow for a rather impressive late season cold air damming wedge to develop across the area. Afternoon highs may remain below 80 and some locations along and north of the I-40 corridor may struggle to reach 70. The wedge likely persists into Saturday before facing its demise by the end of the weekend into early next week. Isentropic ascent atop the wedge in concert with continued moist southwest flow and a passing upper impulse will foster the development of widespread showers and thunderstorms. Surface-based instability will be limited within the wedge, but elevated CAPE above the inversion layer should be sufficient to support at least isolated to scattered thunder even within the cooler air. Guidance continues to paint a wet pattern into next week as well, even as the CAD erodes. Another frontal boundary drops down from the north and may stall near the area keeping continued rain chances around.

AVIATION /00Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: VFR conditions are expected to prevail at most terminals through at least Thursday aftn. A few showers and storms occurred across the mountains, which may support some mountain valley fog development overnight. Guidance still keeps it mostly north of KAVL, and will keep it out of the 00z TAF. Otherwise, convection may linger an hour or two past 00z this evening, with KAVL and KAND having the highest chances of SH or TS in the vicinity. On Thursday...A front approaches the area from the north and will bring greater coverage of afternoon/evening showers and thunderstorms. The peak of this activity is expected to be in 18-23z in the mountains, and 20-03z in the Piedmont, and PROB30s have been added to all sites. Enough coverage of SHRA warrants prevailing or VCSH mention, as well. The front is expected to push into the NC Piedmont around 00z Friday, possibly triggering continued showers and producing MVFR to IFR cigs from NE to SW Thursday night. Winds will stay light mainly out of the SW, but cold be variable around convection, and will toggle to NE behind the front.

Outlook: Cold-air damming across the area by daybreak Friday, and may persist thru Saturday. The CAD will likely produce widespread MVFR to IFR ceilings through the day Friday and into Saturday. Periods of mainly diurnal convection will also continue atop the CAD wedge and into next week, even as the CAD erodes. The potential for overnight fog/low clouds will increase through the period as well.

GSP WATCHES/WARNINGS/ADVISORIES

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