textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Rainfall totals have trended down for the weekend.

Lowered highs on Saturday to account for cold air damming.

Lowered PoPs slightly on Saturday as rain chances should peak Saturday night into Sunday.

KEY MESSAGES

1. Well above normal temperatures and dry conditions stick around for most locations through Friday, outside of the potential for a few showers and thunderstorms in the mountains Friday afternoon/evening. 2. A cold front combined with cold air damming will bring cooler temperatures and widespread rain chances over the weekend, especially Saturday night into Sunday. Locally heavy rainfall is possible but confidence is low. 3. Drier early next week with a brief warm up expected Monday before below normal temperatures return by Tuesday.

DISCUSSION

Key message 1: Well above normal temperatures and dry conditions stick around for most locations through Friday, outside of the potential for a few showers and thunderstorms in the mountains Friday afternoon/evening.

Upper ridging remains over the Southeast through Friday while the western periphery of surface high pressure remains extended over the region through Thursday. This pattern will keep dry conditions around for most locations through Friday, with the exception of the mountains as scattered showers and thunderstorms should develop during peak heating Friday as the western periphery of the surface high nudges eastward ahead of an approaching cold front. A warming trend is expected through Friday ahead of the front, with highs peaking in the upper 80s to lower 90s Friday afternoon. Well above normal temperatures are expected through Friday night.

Key message 2: A cold front combined with cold air damming will bring cooler temperatures and widespread rain chances over the weekend, especially Saturday night into Sunday. Locally heavy rainfall is possible but confidence is low.

A cold front will track across the western Carolinas and northeast Georgia this weekend with hybrid cold air damming developing behind the front. This will allow widespread rain and much cooler temperatures to develop. Cannot entirely rule out some embedded thunder during peak heating each day but confidence is low. Went slightly below NBM for PoPs on Saturday as rain chances should peak Saturday night into Sunday. Rainfall totals over the weekend have trended down slightly compared to the previous forecast. Although 1.5" to 2.0" PWATs are expected to be in place over the weekend, confidence on the heavy rainfall threat remains low due to dry antecedent conditions as well as models being inconsistent run to run regarding where the axis of heavy rainfall will occur. Blended in some of the NBM 10th percentile for highs on Saturday to account for the onset of cold air damming. Highs on Saturday may need to be lowered further depending on how far south the wedge can develop so confidence on the current forecast highs for Saturday is low. Much cooler and below normal highs are expected on Sunday. Lows Saturday night and Sunday night will remain above normal thanks to widespread rain and thick cloud cover.

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

Dry high pressure builds in from the northwest on Monday and lingers through at least mid-week. The latest GFS keeps rain chances around on Monday while the EURO and Canadian have dry conditions returning Monday. The latest NBM appears to be more in line with the GFS showing chance PoPs across nearly the entire GSP forecast area on Monday. Thus, confidence on Monday PoPs is low. Confidence is higher regarding dry conditions Tuesday into Wednesday. Highs on Monday should rebound to near normal before dropping back below normal Tuesday and Wednesday. Lows should drop into the upper 40s across the North Carolina mountains Monday night and Tuesday night, with locations above 3500 ft possibly seeing lows drop into the upper 30s Tuesday night.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

At KCLT and elsewhere: Dry and VFR through the 18Z TAF period outside of the potential for another round of mountain valley fog and low stratus overnight into early Thursday morning. Went with a TEMPO at KAVL from 09Z-13Z for IFR vsbys and LIFR cigs. Vsbys and cigs at KAVL may drop down to VLIFR again like this morning but confidence is too low at this time to go that pessimistic. Winds are mostly light and VRB this afternoon but should gradually pick up out of the S/SW. Wind go calm to light and VRB again this evening into early Thursday morning before picking up out of the S/SW again mid to late morning. Wind speeds will generally range from 3-6 kts. Cirrus will stream overhead periodically through the TAF period, with some cumulus developing each afternoon.

Outlook: Dry and VFR through Thursday night outside of the potential for mountain valley fog/low stratus Friday morning. Moisture will begin to increase across the area Friday afternoon/early evening, mainly across the mountains. More widespread showers and associated restrictions develop ahead of a cold front this weekend.

GSP WATCHES/WARNINGS/ADVISORIES

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