textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Shower and thunderstorm trends updated based on radar and latest forecast guidance.

The aviation forecast updated for the 00Z TAF issuance.

KEY MESSAGES

1. Isolated showers and thunderstorms cross the Piedmont early this evening. An isolated severe storm is possible until the storms move east. Additional isolated showers and thunderstorms are possible across the mountains this evening. 2. Drier weather returns Sunday through early next week, followed by daily shower and thunderstorm chances returning Wednesday through Friday.

DISCUSSION

Key message 1: Isolated showers and thunderstorms cross the Piedmont early this evening. An isolated severe storm is possible until the storms move east. Additional isolated showers and thunderstorms are possible across the mountains this evening.

The first area of convection is winding down across the Upstate and NE GA but lingers across the NC Piedmont. A strong to severe storm with damaging winds remains possible until these storms move east of the area early this evening. A second area of isolated convection to our NW along a frontal boundary may move into the mountains later this evening but they should weaken as they move toward our area. Otherwise, expect clearing skies overnight with another round of mountain valley fog.

Key message 2: Drier weather returns Sunday through early next week, followed by daily shower and thunderstorm chances returning Wednesday through Friday.

The surface front should settle southward most of the way through the CWA by Sunday morning. Closed 500mb low will remain over the northern Great Lakes, only slowly progressing eastward into the St Lawrence Valley as vortices rotate through. The axis of the surrounding trough in turn makes slow progress across the Eastern Seaboard through the early week period; deep anticyclone will remain over the southern Rockies and Plains. NW flow should continue over our area in the low levels with westerly upper flow; some mixing of drier air should occur diurnally on Sunday, effectively pushing the front southward, and it then should stall over the Deep South by Monday. The upshot for our area still looks to be mostly sunny skies and minimal chances for convection Sunday and Monday. Temperatures will remain near normal though the humidity will be low.

We may experience height falls Tuesday with another weak shortwave entering the eastern trough, so it is not out of the question the front will reactivate on our southern fringe, and allow some convective activity to develop along that part of our CWA border. However, most indications are we will remain on the cool/dry side of the front and humidity and PoPs are still forecast below normal. Height falls begin more earnestly Tue night into Wed as better defined shortwave enters the MS Valley and the front thus is more likely to shift northward. For Wednesday in turn we expect seasonably hot and humid conditions to return, with PoPs in the usual 20-30% range; chances increase Wed night and Thu as the trough interacts with the front. Though the large scale pattern looks likely to feature a western ridge and eastern trough through the end of next week, models differ as to whether a drying cold front will follow the shortwave. and for now the safest bet is to assume unsettled weather (high humidity and frequent chances for showers/storms) will continue to the end of the period, though temperatures will be advertised near or even slightly below normal.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: Isolated convection should stay north of KCLT this early evening but could move close by. Have kept mention out for now but will amend if a cell approaches. Otherwise, VFR with winds becoming light this evening. Expect another round of IFR to LIFR fog/stratus at KAVL overnight despite some northerly wind. Can't rule out a restriction at KHKY but chance too low for the TAF. VFR expected elsewhere. A drier air mass moves in Sunday with no significant chance of convection and only some high based VFR Cu. Winds become N to NW through the day with low end gusts at KAVL. KAND will see a westerly wind.

Outlook: No significant chance of convection until Wednesday with an even better chance on Thursday. Mountain valley fog and low stratus is possible each morning.

GSP WATCHES/WARNINGS/ADVISORIES

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