textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Gusty winds linger this evening then diminish overnight.

Humidity remaining low each afternoon on Thursday and Friday.

Updated details on precipitation event Saturday night through Sunday night.

KEY MESSAGES

1. Rain ending with gusty winds behind a departing cold front. 2. A cooler and drier air mass moves into region this through Friday, with low relative humidity each afternoon. 3. Widespread rain is expected over the weekend, with precipitation most likely Saturday night and Sunday. This generally should be beneficial rain for most of the area. Localized heavier rainfall is possible, which could lead to nuisance flooding of poorly drained areas, and/or isolated bankfull conditions on area streams.

DISCUSSION

Key message 1: Rain ending with gusty winds behind a departing cold front.

Patchy rain will move south of the area this afternoon behind a departing cold front. Gusty NW winds will linger into the evening as well before winds diminish overnight. Lows will be much cooler than this morning ending up around normal.

Key message 2: A cooler and drier air mass moves into region this through Friday, with low relative humidity each afternoon.

Dry and cooler high pressure builds into the area Thursday and remains in place on Friday. Highs will be near normal both days. With the drier air mass, minimum RH will still fall to near or below 25% for most locations east of the mountains, and in some mountain valleys, both days. Winds will be much lighter with some lingering high elevation gusts on Thursday. The low RH may lead to some fire weather concerns even with the lighter winds.

Key message 3: Widespread rain is expected over the weekend, with precipitation most likely Saturday night and Sunday. This generally should be beneficial rain for most of the area. Localized heavier rainfall is possible, which could lead to nuisance flooding of poorly drained areas, and/or isolated bankfull conditions on area streams.

Strong shortwave trough will eject out of the southern Rockies into the Southern Plains on Saturday, inducing increased downstream ridging over the Southeast and OH Valley during the day. With surface high pressure moving offshore, return flow will increase ahead of the deepening surface low. Precipitation will increase Saturday evening from the west as the warm front lifts into the area, increasing isentropic upglide. With the surface high offshore, it will certainly not be in a favorable position for damming, but insitu CAD will likely develop into Sunday, enhancing upglide and dropping high temperatures back down below normal, probably lower than NBM highs so continued trend of blending CONSRaw into the forecast for Sunday. Surface high in SE Canada does not look to set up quickly enough for the system to tap into the CAA, and with this it seems unlikely that temperatures will reach critical thresholds anywhere for mixed or frozen precip, with the possible exception of the top of Mt. Mitchell. Have continued trend of not including any at this time.

Meanwhile, moisture flux increase significantly especially early Sunday in the SW flow aloft, and guidance is in good agreement on a soaking rain overspreading the area. The 12z-18z timeframe Sunday morning could see periods of heavy rain especially in the typical band along the SC/NC/GA state line including the SW NC mountains/SC Mountains/extreme NE GA, enhanced by terrain, frontogenesis along the wedge front, and strong LLJ upwards of 50kt. In addition, weak MUCAPE may contribute to enhanced rainfall rates (and cannot rule out some thunder in southern Piedmont zones). A quick inch is certainly possible within this 6h timeframe in these areas, with storm total of over 2" possible. The rest of the Piedmont areas will likely see over an inch, with the lowest amounts in the rain shadow areas of the French Broad and nearby areas downwind from the escarpment. Hydro concerns are generally minimal, but some HEFS hydro model members bring the upper reaches of the French Broad to action, with an outlier of possibly minor flood stage at Blantyre. Still plenty of uncertainty on details of potential impacted basins as slight shifts in location or extent of heaviest rain will have downstream effects, and so will continue to refine as we get closer. Rates will have to be monitored for flash flood potential, but mitigated by dry antecedent conditions across the area.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

At KCLT and elsewhere: Patchy rain and MVFR cigs have moved south of the terminals. Gusty NW winds and a few low VFR clouds will remain through the afternoon. Gusts linger at KAVL/KGSP/KGMU into the evening but winds become light N elsewhere with mainly cirrus overnight. Light N to NW wind expected for all but KAVL on Thursday where gusty N wind returns. That said, can't rule out some low end gusts as mixing begins elsewhere. Just cirrus expected on Thursday.

Outlook: Dry and VFR through Friday night before precipitation chances and associated restrictions return this weekend ahead of a low pressure system.

GSP WATCHES/WARNINGS/ADVISORIES

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