textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Rainfall totals have trended up slightly for the weekend.

Updated the aviation discussion for the 06Z TAF issuance.

KEY MESSAGES

1. Temperatures remain well above normal with dry conditions expected for most locations through Friday, outside of the potential for a few showers and thunderstorms Friday afternoon and evening, mainly in the mountains. 2. Cold air damming will set up over the area, bringing cooler temperatures and widespread rain chances over the weekend, especially Saturday night into Sunday. Locally heavy rainfall is possible. 3. Drier early next week with a brief warm up expected Monday before below normal temperatures return by Tuesday.

DISCUSSION

Key message 1: Temperatures remain well above normal with dry conditions expected for most locations through Friday, outside of the potential for a few showers and thunderstorms Friday afternoon and evening, mainly in the mountains.

Upper ridge continues to build over the Southeast today, then begins to flatten, as a northern stream trough forms across Great Lakes. Sfc high pressure will remain centered east of the Outer Banks, with anticyclonic flow over the Carolinas, keeping deeper moisture at bay. Temperatures will be around 8-12 deg above normal thru Friday. Friday is expected to be the warmest day of the week, with highs well into the 80s in the lower elevations, and around 90s in portions of the Lakelands and southeast of Charlotte.

Moisture advection starts to ramp up Friday ahead of a cold front pushing into the Ohio Valley. Steepening lapse rates and increasing low-level moisture will result in a few hundred J/kg of sbCAPE across the western mountains, thus a return of scattered showers and perhaps, an isolated thunderstorm or two will be possible.

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

The latest models have come into better agreement on a cold front slipping into the area during the day Saturday. This timing will make the max temp forecast a bit tricky, as increasing low clouds, NE wind and showers will lead to cooler temps in the north, but depending on how far the front can get by late aftn, the southern areas may still see another warm day. Overall, the trend has been for a slightly earlier arrival, and thus, max temps have been trending cooler.

Hybrid cold-air damming should be well in place by Saturday night, with a mid-level trough providing support for more widespread rain, while sfc high pressure builds into the Northeast states. PWATs will be high atop the CAD wedge, but low-level flow remains weak, and guidance continues to lack much signal for anything more than localized heavy rainfall. With that said, most areas should get a nice beneficial soaking rainfall, with precip lasting thru the day Sunday. With solid CAD in place, most of the area will likely be too stable for thunder, except for the southwestern NC mountains, like Smokies and Balsams, which will be on the edge of the wedge. This doesn't necessarily mean heavy rain rates won't be possible, as the high PWATs and deep warm cloud layer on forecast soundings suggest even showers could be efficient rain producers. There may also be elevated CAPE above the wedge to support some thunderstorm chances. With the CAD, highs should be about 5-10 deg below normal.

Precip is expected to start tapering off overnight Sunday night. The 18z GFS has finally come in line with the ECMWF and Canadian on pushing the front south of the area and dry air filtering in from the north, cutting off PoPs for Monday. The NBM continues to lag this trend, and has chance PoPs across the southern half of the CWFA. These PoPs are most likely overdone, given the expected progressive flow pattern.

Key message 3: Drier early next week with a brief warm up expected Monday before below normal temperatures return by Tuesday.

An upper trough will dig and shift to the East Coast Monday, establishing a longwave trough over the eastern CONUS thru most of next week. This will allow a nice fall air mass to settle over the Great Lakes to the Mid-Atlantic, with dry conditions and seasonably cool conditions nosing south into the forecast area. After a mild day with near- normal temps Monday, highs will be mainly in the 60s to lower 70s Tuesday and Wednesday (a few degrees below normal), with lows in the 40s and even into the 30s in the highest elevations Tuesday night.

AVIATION /06Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: Expect dry, VFR conditions to continue thru the 06z TAF period. The only exception is likely to be another round of mtn valley fog/low stratus overnight and into the morning. With mostly clear skies, light to calm winds, and KAVL already near their crossover temperature, I think there's a pretty good chance they will see some restrictions overnight/into the morning. As such, I kept the TEMPO for LIFR cigs/visby from 09 to 13z. Any restrictions should burn off by 14z or so. Otherwise, I expect a few fair-weather cumulus and high cirrus today. Winds should remain light and VRB to calm thru the morning and then pick up out of the S/SW this afternoon. They will go light and VRB again later this evening.

Outlook: Dry and VFR thru at least Friday morning, outside of the potential for mtn valley fog/low stratus Friday morning. Moisture will begin to increase across the area Friday aftn/early evening, mainly across the mtns. More widespread showers and associated restrictions develop ahead of a cold front this weekend.

GSP WATCHES/WARNINGS/ADVISORIES

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