textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated the aviation discussion for the 18Z TAF issuance.

KEY MESSAGES

1. Hot and humid conditions continue today through much of the weekend with at least scattered showers and storms, especially tomorrow. 2. A backdoor cold front pushes through the area on Monday bringing drier but still warm weather through much of next week, excluding daily mountain showers/storms.

DISCUSSION

Key message 1: Hot and humid conditions continue today through much of the weekend with at least scattered showers and storms, especially tomorrow.

A weak split flow regime remains draped across the CONUS today with strong northern stream flow extending from the Northern Rockies across the Northern Plains and into southeast Canada. Farther south, a weaker branch of southern stream flow is situated from the Desert Southwest across the Southern Plains and into the southeast states. Within the southern stream, a weak shortwave trough with a closed upper low is sliding across the Mississippi Valley and into western Tennessee. This feature will cross the Southern Appalachians tomorrow with general troughing lingering into Sunday. An unseasonably warm and humid airmass is entrenched across the region with afternoon highs today soaring well above average into the upper 80s to low 90s. Weak height falls ahead of the approaching trough in concert with a late summer airmass will help instigate at least isolated to widely scattered showers and thunderstorms this afternoon, especially south of I-85. A few of these storms may become strong to marginally severe with the main hazard being locally damaging winds.

The passage of the upper trough tomorrow will provide more notable forcing with the 12z suite of CAMs in generally good agreement on scattered to numerous afternoon/evening showers and thunderstorms across much of the area. Near-storm forecast soundings reveal tall skinny CAPE profiles with modest DCAPE. While not overly impressive, a few isolated strong to severe storms with locally damaging winds cannot be ruled out again on Saturday. Associated cloud cover will help to keep temperatures a few degrees cooler compared to today, but still above climo for mid September. The upper trough axis gradually pivots across the region on Sunday and another bout of isolated to widely scattered showers and storms can be expected, but of lesser coverage compared to Saturday.

Key message 2: A backdoor cold front pushes through the area on Monday bringing drier but still warm weather through much of next week, excluding daily mountain showers/storms.

Heading into the start of next week, a notable northern stream trough is progged to swing across the Great Lakes and into New England Sunday night into Monday. A sprawling surface high quickly translates into the Mid-Atlantic and New England and in turn drives a back door cold front down the Appalachians through Virginia and across the Carolinas. A few isolated showers and/or a storm may accompany the front, but it will mainly be a dry frontal passage for most. Temperatures ahead of the front will once again climb back into the upper 80s to low 90s. For the remainder of the week, stout upper ridging builds back over the Southern Appalachians with guidance indicating 500mb heights nearing 598dam. Gross. Despite persistent dry northeast flow afternoon highs will rebound through the week with upper 80s to near 90 common again by Thursday and Friday, which remains well above climo for mid September. Dry air will also shunt deeper moisture to over the mountains which is where the best chances for a few diurnal showers and storms will reside.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

At KCLT and elsewhere: VFR conditions are ongoing this afternoon and expected to prevail through most of the TAF period. Isolated to widely scattered showers and thunderstorms could bring brief impacts to the I-85 terminals (KAND/KGMU/KGSP/KCLT) this afternoon and early evening. Thereafter, at least some degree of low stratus is expected to develop overnight, but the extent of which remains low confidence. TEMPO groups have been carried in the more likely locations along with traditional valley fog/stratus at KAVL. Any morning fog/stratus should mix/scatter after sunrise with a return to VFR. Greater coverage of afternoon/evening showers and storms is expected Saturday. Otherwise, winds are expected to remain light out of the south/southwest.

Outlook: Scattered afternoon and evening storms will once again be possible Sunday. Storm chances shift to the mountains Monday through much of next week. Mountain valley fog/stratus will be possible any given morning, especially in prone/traditional locations.

GSP WATCHES/WARNINGS/ADVISORIES

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