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 18Z 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 /18Z WEDNESDAY THROUGH MONDAY/

At KCLT and elsewhere: VFR conditions are expected to prevail at most terminals through the period. An afternoon cumulus field is in the process of developing across the area along with high clouds streaming overhead. Coverage of afternoon showers and storms should remain limited to the mountains this afternoon and evening where a PROB30 has been carried at KAVL. A generally quiet overnight period is expected, but a few instances of mountain valley fog cannot be discounted, especially where rainfall occurs today. A front approaches the area tomorrow and will bring greater coverage of afternoon/evening showers and thunderstorms. Most of this activity will occur after the current 18z end time of the TAF, but went ahead and included mention at KCLT for the end of the 30 hour TAF period.

Outlook: An approaching front and increasing moisture will bring a more active pattern for mainly afternoon and evening showers and thunderstorms beginning Thursday afternoon and then continuing through the end of the week. Cold-air damming may produce widespread MVFR to IFR ceilings through the day Friday. The potential for overnight fog/low clouds will increase through the period as well.

GSP WATCHES/WARNINGS/ADVISORIES

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