textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

No major changes to the latest forecast.

Updated the aviation discussion for the 00Z TAF issuance.

KEY MESSAGES

1. Well above normal and dry through Friday for most locations, outside of the potential for a few mountain showers and thunderstorms Friday afternoon/evening. 2. Cold air damming will set up over the area behind a cold front, bringing cooler temperatures and widespread rain over the weekend, especially Saturday night into Sunday. Locally heavy rainfall is possible but confidence is low. 3. Dry next week with a brief warm up on Monday before below normal temperatures return Tuesday into Wednesday.

DISCUSSION

Key message 1: Well above normal and dry through Friday for most locations, outside of the potential for a few mountain showers and thunderstorms Friday afternoon/evening.

Upper ridge continues building over the Southeast will linger over the region through Friday night, keeping warm and well above normal temperatures around. Highs peak on Friday, climbing into the upper 80s to lower 90s east of the mountains. At the surface, the western periphery of high pressure will remain extended over the Southeast through Friday morning before nudging eastward in response to a cold front approaching out of the west. This will act to keep dry conditions around for most locations through Friday night, although moisture will return in the form of scattered showers and thunderstorms across the mountains Friday afternoon and evening. Severe weather is not expected.

Key message 2: Cold air damming will set up over the area behind a cold front, bringing cooler temperatures and widespread rain over the weekend, especially Saturday night into Sunday. Locally heavy rainfall is possible but confidence is low.

A cold front tracks across the forecast area this weekend, with hybrid cold air damming building in behind the front. This will allow widespread rain to develop, especially late Saturday into late Sunday. The main concern will be heavy rainfall leading to nuisance to minor hydro issues thanks to forecast PWATs ranging from 1.5 to 2.0 inches. However, there is still quite a spread among the models regarding weekend rainfall amounts. The NAM is the most bullish with rainfall totals across the GSP forecast area while the Euro shows the heaviest rainfall occurring south and east of the GSP forecast area. The GFS lies somewhere in the middle. NBM seems to align more with the GFS, showing roughly 1 to 2.5 inches of rainfall for most locations with locally higher totals of 3+ inches possible. Thus, confidence on rainfall totals remains low. With dry antecedent conditions in place and models disagreement on where exactly the swath of heavy rain will occur, confidence also remains low regarding the heavy rainfall/hydro threat.

With stable cold air damming in place all weekend, the severe threat will remain very low, if any. Could not rule out some embedded thunderstorms, especially during peak heating Saturday, but confidence is low as this will be determined by how far south the wedge is able to build on Saturday. The potential for embedded thunder will be much lower on Sunday as the wedge strengthens. The exception will be the Southwest North Carolina mountains as these areas will be under less of an influence from the wedge.

Highs on Saturday will be tricky and also dependent on how far south the wedge builds. If the wedge remains farther north then highs could end up above normal for most locations. If the wedge builds farther south, then temperatures would end up much cooler. Thus, confidence remains low on highs for Saturday. The wedge will build southward Saturday night into Sunday, allowing for much cooler and below normal highs on Sunday. Lows through the weekend will end up a few to several degrees above normal thanks to thick cloud cover and widespread rain.

Key message 3: Dry next week with a brief warm up on Monday before below normal temperatures return Tuesday into Wednesday.

Upper troughing will be the dominate feature aloft from the Northeast down to the Mid-Atlantic much of next week. At the surface, dry high pressure will build in from the northwest Monday into Tuesday, lingering over the region through the rest of the workweek. The GFS continues to show rain lingering through Monday across portions of the GSP forecast area while the Euro continues to show dry conditions returning by early Monday morning. The Canadian lies somewhere in between the GFS/Euro. NBM PoPs remain in line with the GFS. However, thinking is that NBM PoPs are overdone on Monday and that dry conditions should return quicker than what the GFS/NBM show. Highs on Monday rebound near normal, dropping below normal Tuesday into Wednesday. Highs on Thursday may return to near normal. Tuesday night should be the coldest night with lows across the higher elevations of the North Carolina mountains dipping into the upper 30s to lower 40s. There are no frost concerns at this time.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

At KCLT and elsewhere: Mostly VFR conditions will prevail through the forecast period outside of mountain valley fog/low stratus early Friday morning. For this, decided to maintain the TEMPO for vsby and cig restrictions at KAVL from 09Z to 13Z. Light and variable winds overnight will pick up out of the south to southwest at 4-8 kts by Friday afternoon. Can't rule out an isolated shower or thunderstorm over KAVL Friday afternoon, but confidence is too low for a TAF mention at this time. Should start to see instances of increasing mid to high clouds along with diurnal cumulus Friday afternoon and evening, ahead of the next storm system that will impact the area over the weekend.

Outlook: Scattered showers and thunderstorms, as well as associated restrictions, return across the mountains Friday afternoon and evening. Mountain valley fog and low stratus remain possible Friday night. More widespread showers and associated restrictions develop ahead of a cold front this weekend. Dry and VFR conditions return behind the front early next week.

GSP WATCHES/WARNINGS/ADVISORIES

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