textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Cooler highs on Thursday than previous forecast.

Rain chances trending lower for Friday.

KEY MESSAGES

1. Rain chances will return to the forecast area tonight with a developing frontal zone. Rain is most likely Thursday then slowly tapering off through Friday from northwest to southeast. The chance of flooding currently looks low. 2. Drier conditions return Friday into the weekend before rain chances return next week. A Warming trend is expected through the weekend before cooler temperatures return early next week.

DISCUSSION

Key message 1: Rain chances will return to the forecast area tonight with a developing frontal zone. Rain is most likely Thursday then slowly tapering off through Friday from northwest to southeast. The chance of flooding currently looks low.

A cold front will sag south into the area by this evening, but it looks to stall with moistening return flow across the TN Valley and southern Appalachians tonight into early Thu, basically leaving a stationary front over the area. Some mechanical lift into the W and SW facing ridges will lead to chance PoPs by early evening. Shortwave energy and frontogenetic response leads to a band of QPF showing up in most models across TN and NC overnight into early Thu which results in a swath of 50-80% PoPs extending across the CWA. Lows will be 10 to 15 degrees above normal keeping precip all liquid. Wind gusts should diminish outside of the mountains but will linger across the higher elevations.

Another shortwave swings across the area on Thursday with a surface wave forming and moving along the front. This keeps high precip chances over the area through the day. The front begins to move south during the evening as the shortwave and surface low move east of the area. This will cause precip to taper off from NW to SE overnight. Fairly high PW values and good forcing will lead to storm total QPF amounts 1 to 2 inches across the mountains and 0.5 to 1.25 inches outside of the mountains. Given the ongoing drought conditions, this should remain in the beneficial rainfall category with only a minimal chance of any flooding. Some weak instability does develop, generally south of the I-85 corridor. Can't rule out some thunder rumbles but no severe storms are expected. Gusty winds return ahead of and behind the front, but should also remain below advisory level.

Highs Thursday are a little tricky with clouds and precip and the NAM showing some in situ CAD potential across the I-40 corridor. Have blended some of this into the forecast with highs a little lower than the NBM which still ends up around normal. Lows around 10 degrees above normal Thursday night.

Key message 2: Drier conditions return Friday into the weekend before rain chances return next week. A Warming trend is expected through the weekend before cooler temperatures return early next week.

Surface high pressure builds across the region Friday into the weekend behind a departing cold front allowing drier conditions to return. However, some moisture may linger behind the front on Friday, but confidence is low as the majority of the morning CAMs have dry conditions developing behind the front. Thus, opted to go lower than NBM PoPs on Friday and capped PoPs to slight chance (<25%). A warming trend can be expected through the weekend, with highs ending up around 10-15 degrees above normal. Afternoon temperatures on Sunday will climb into the lower to mid 70s east of the mountains.

Warmer temperatures combined with the drier air mass will allow dewpoints to fall into the mid 30s to mid 40s each afternoon over the weekend, leading to the return of lower humidity. LREF probabilities only show a 15% to 30% chance of minimum RH values falling below 35% Saturday afternoon, mainly across the mountains. LREF probabilities show a 25% to 45% chance of minimum RH values falling below 35% Sunday afternoon, mainly along/south of I-40. How quickly we dry out on Friday, as well as how far south the front sinks, will determine how low minimum RH will be able to fall this weekend. For now, it appears that any fire weather concerns will be very low as winds should remain fairly light outside the higher elevations.

A cold front tracks across the forecast area on Sunday before stalling just south of the forecast area early next week. This will allow rain chances to return by early next week. A cooling trend can be expected Monday into Tuesday as cold air damming develops behind the stalled front. This will allow below normal highs to return by Tuesday.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

At KCLT and elsewhere: MVFR cigs have creeped into KAND and could reach KGMU/KGSP this afternoon but that's uncertain. VFR expected elsewhere. Gusty SW wind, NW at KAVL, will continue through the afternoon as well. Although, winds could toggle back to SW at KAVL for a period. Guidance continues to slow the onset of low clouds overnight and have followed suit. Expect showers and MVFR cigs/vsby to develop overnight, with IFR cigs, and possibly vsby, holding off until after daybreak. Showers will become more steady overnight into the day Thursday. A rumble of thunder is possible at the SC sites, but chance too low for the TAFs at this time.

Outlook: A cold front tracks east of the area by Friday, but showers and associated restrictions linger through Thursday night. Dry and VFR conditions Friday into the weekend. Another front may bring showers and associated restrictions on Monday.

GSP WATCHES/WARNINGS/ADVISORIES

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