textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

No significant changes to the forecast with this package.

KEY MESSAGES

1. A cold front will bring spotty showers, and possibly a thunderstorm, this afternoon and evening. Brief period of cooler weather through Thursday and Thursday night. 2. Dry weather returns to end the week, with temperatures warming and humidity gradually increasing over the weekend and early next week.

DISCUSSION

Key message 1: A cold front will bring spotty showers, and possibly a thunderstorm, this afternoon and evening. Brief period of cooler weather through Thursday and Thursday night.

A cold front is progged to move across the CWFA later this afternoon and evening as an upper trough slides over the Great Lakes region and Northeast. Forcing for ascent is modest to go along with a moisture starved airmass. CAMs continue to show a line of showers and thunderstorms developing over the immediate TN before gradually weakening as it pushes further east, especially outside of the mountains. A quick shower shot cant be ruled out east of the mountains, but latest trends have slightly lowered in overall coverage, with the best chances being in the northern Upstate and NC Piedmont during the evening timeframe. Otherwise, the front will make a clean passage overnight tonight as CAA fills in behind it with weak high pressure spilling over the region tonight into Thursday.

Under confluent upper flow between the Northeast CONUS cutoff low and a ridge moving into the Mississippi Valley, dry surface high pressure will shift across the southern Appalachians through Thursday and Friday before centering east of the CWA. Max temps look to trend cooler across the area Thursday, as much as 10 degrees cooler across the mountains and northern foothills, but with downslope NW winds offsetting the CAA across most other areas for a less noticeable drop. Modest wind gusts appear likely Thursday given the gradient flow across the higher terrain and good mixing in the downslope areas. However, the models that explicitly forecast gusts, such as the ECMWF and HRRR, have both trended lower in their depictions for Thursday. RH still is expected to dip to the 25-30% range in the Piedmont. Thursday night, skies become virtually clear and winds relax as the high centers over the CWA, though not necessarily quickly enough to ensure prime radiational cooling conditions. Sheltered areas such as small mountain/river valleys would be the exception. Mins Thu night into Fri morning will be around 10 below normal for the Piedmont, 10-15 in the mountains. A few isolated mountain spots could dip to the mid 30s and light frost could result there.

Key message 2: Dry weather returns to end the week, with temperatures warming and humidity gradually increasing over the weekend and early next week.

Light southwest flow is restored over the region Friday with the high centering offshore and heights rising aloft. Temps moderate and trend a few degrees warmer, especially in mountain valleys prone to downsloping in SW flow; despite some moisture return low RH near 30% is forecast once again, with still lower RH in those same mountain valleys. Upper pattern turns quasi-zonal over the Southeast Saturday, with airmass continuing to modify; upper ridge builds over the Southeast Coast for Sunday leading to still warmer temperatures. Humidity won't be quite as low, but still somewhat below normal for late May. Temps hold fairly steady Monday and Tuesday but humidity will trend higher.

Models and ensemble members still generally depict a front stalling in the Ohio Valley Saturday, but have not come into any better agreement as far as whether any convection developing along it will propagate into our CWA from the west, so we retain only 10-20% PoPs Saturday and Sunday over the NC mountains. Weak diurnal instability may develop Sunday and Monday, but lacking much of a trigger precip chances remain low. A cold front will approach the area Tuesday, and in the prefrontal environment PoPs increase to 20-30% over the mountains, but the latest ensembles indicate the better chance would be Wednesday. Probably not looking at any appreciable rainfall until after the end of the current forecast period. With the setup appearing to favor nonsevere pulse storms Tuesday, localized heavy rainfall could occur but not providing real drought relief.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

At KCLT and elsewhere: VFR through much of the forecast period. A cold front will move in this evening and develop a line of showers, with some embedded thunder possible. The best chances are at the North Carolina terminals, so kept the PROB30 mention for SHRA and associated restrictions this afternoon/evening. Some mid and upper level clouds will move across the area. Can't rule out low cigs in the vicinity of a heavier shower or storm, but cigs expected to remain at VFR. South to southwest winds ahead of the front, will turn northwesterly behind the front late this evening into the overnight hours. Can't rule out some low-end gusts during the front's passage, but better chances of gusty winds are expected later Thursday morning into the afternoon. Included a low-end gust mention at all sites and bumped up gusts at KAVL where gusts up to 25-30 kts can't be ruled out.

Outlook: VFR and quiet weather is expected for the rest of the week. Moisture begins to increase out of the south over the weekend, but confidence on a return to any diurnal convective rain chances remains low.

GSP WATCHES/WARNINGS/ADVISORIES

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