textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Timing of rain chances have trended a little earlier, but uncertainty remains high on the details of severe and heavy rain threat Thursday through Friday.

Updated aviation discussion for the 12z TAFs.

KEY MESSAGES

1. Dry with below-normal temperatures and comfortable humidity today. Rain chances remain low overall, but a few showers are possible in the lower Piedmont this evening through Wednesday. 2. Humidity and rain chances increase Thursday, with periods of rain and gusty winds likely at times Thursday afternoon through Friday evening. Locally heavy rainfall and stronger, damaging winds cannot be completely ruled out either of those days. Drier air is expected to return for the weekend.

DISCUSSION

Key message 1: Dry with below-normal temperatures and comfortable humidity today. Rain chances remain low overall, but a few showers are possible in the lower Piedmont this evening through Wednesday.

Pleasant temperatures and humidity expected today for mid-June, as the forecast area remains north of a stalled front that is draped roughly across the I-20 corridor. A steady stream of high clouds with occasional mid clouds will continue thru the day, helping keep temps even cooler with highs 5-9 degrees below normal.

The front will begin to lift back north as a warm front in response to a strong shortwave rotating thru the longwave trough over the Great Lakes to Mid-MS Valley. Moisture advection and isentropic lift could produce some showers and perhaps a rumble of thunder across the far southern portions of the forecast area this evening. Otherwise, increasing low clouds and light SW winds will keep low temps around normal. The shortwave passes by the east, veers flow to more westerly and helps clear out clouds Wednesday. Guidance still shows relatively stable soundings despite a rebound in temps back to around normal. Some showers may develop in the far western mountain zone Wednesday evening, aided by upslope flow. Muggier dewpts and expanding low clouds will keep low temps about 5-10 degrees above normal Wednesday night.

Key message 2: Humidity and rain chances increase Thursday, with periods of rain and gusty winds likely at times Thursday afternoon through Friday evening. Locally heavy rainfall and stronger, damaging winds cannot be completely ruled out either of those days. Drier air is expected to return for the weekend.

The 00z suite of models are coming into a little better agreement on a tropical disturbance drifting out over the NW Gulf and then getting picked up by a digging longwave trough over the central CONUS. The longwave trough will bring a cold front into the Southeast, while the tropical low drifts ENE over the Lower MS Valley. The combination of the approaching front and the tropical wave will enhance low-level SWLY flow atop the forecast area, and results in unusually windy conditions for this time of year. The NBM continues to forecast 25-35 mph gusts Thursday aftn. As far as PoPs, there is still some disagreement on how strong and fast the wave will be as it tracks east ahead of the front. The 00z GFS is very weak and tracks the wave more to our south. While the ECMWF continues to be stronger outlier (albeit trending weaker), and tracks a compact low across our southern border Friday morning. The Canadian has what looks like a strong MCS barrel thru the I-85 corridor Thursday night. All this to say that there may be a period of severe and/or heavy rain threat at some point between Thursday aftn and Friday evening, depending on how the tropical disturbance and cold front interact. The model consensus is for the front to push thru the area by Friday evening, ushering in drier air. It will be noticeably more humid Thursday with tropical moisture coming in, with highs slightly above normal. Friday should be slightly cooler with the front pushing in.

The weekend looks fairly dry with temps at or slightly below normal. Quasi-zonal upper flow will continue into next week, resulting in another front approaching from the NW and bringing rain chances for Monday. Temps overall will be near to slightly above normal.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

At KCLT and elsewhere: Generally thick high clouds are expected to persist across the area today, with some areas of mid clouds underneath. Ceilings will remain VFR until this evening, when MVFR clouds may expand from the SW. Guidance has backed off the extent of the lower clouds, but still shows at least MVFR cigs affecting the Upstate sites overnight. Will continue to show just SCT MVFR clouds around KCLT late tonight thru about 14z Wed. There may also be some showers skirting the southern part of the area this evening, warranting a PROB30 at KAND, as well. Winds overnight starting out out of the NE or light and variable, then pick up out of the SW around midday thru the aftn 6-12 kt. Low-end gusts at KAVL will be possible in the aftn. Winds stay SW tonight and become light.

Outlook: Any IFR or MVFR clouds are expected to scatter out by late morning Wednesday. A similar setup may occur again Wednesday night into Thursday morning. More widespread convection is expected across the area Thursday thru Friday, then dry weather returns Saturday.

GSP WATCHES/WARNINGS/ADVISORIES

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