textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

No significant changes to forecast thinking for the next several days.

KEY MESSAGES

1. Above-normal temperatures persist into the weekend. Starting Tuesday, chances for showers and thunderstorms mainly in the afternoons. 2. Cold front appears likely to cross the area Sunday or Sunday night, offering the best chance for widespread rainfall between now and early next week.

DISCUSSION

Key message 1: Above-normal temperatures persist into the weekend. Starting Tuesday, chances for showers and thunderstorms mainly in the afternoons.

Upper level pattern across the CONUS starts out quasi-zonal today, with a very broad low-amplitude ridge atop most areas east of the Rockies. The midlatitude wave train will ride atop this ridge and thus be kept well to our north, across the Great Lakes and Northeast. Bermuda high extends inland over the Southeast states. Over the course of the week, the pattern gradually amplifies.

Mid- to late-spring like sensible weather will continue for several more days. Southerly winds will promote moisture return such that humidity will remain higher through the afternoons as compared to this past weekend. This should help mitigate fire weather concerns to some degree, though fuel moisture is not likely to rebound significantly until rain occurs. Burn bans remain in effect as of Monday. The better moisture will promote diurnal destabilization, making showers/storms possible Tuesday and beyond. As usual in the warm season, the best daily chances will be over the mountains and in the afternoon. Severe weather is not expected with CAPE values being kept relatively low by mediocre lapse rates, and with weak shear under the influence of the ridge. Model QPF response is slightly better Wednesday than either Tue or Thu, seemingly with enhanced moisture advection into the front stalling in the Ohio Valley at that time. PoPs follow the same trend. The amplifying pattern suggests the low-level flow will back toward the south or south-southeast late in the week, suggesting slightly better fetch off the Atlantic Thursday night through Saturday, increasing PWAT and bringing daily PoPs somewhat higher. Non-diurnal precip activity looks more plausible in that timeframe as the sea-breeze front is more likely to reach the area. Altogether, not seeing much to suggest potential for heavy rain at any point through Saturday, with weak forcing suggesting only hit-or-miss precip. The south-facing Blue Ridge Escarpment will however have the best potential for recurring showers through the week, and so LREF ensemble probs of 1" total rain through Saturday are highest there--though still low.

Temperatures trend warmer through Thursday, but then hold steady or trend a bit cooler due to increased moisture aloft suggesting more cloud cover. They however remain on the order of 10-15 degrees above normal through Saturday.

Key message 2: Cold front appears likely to cross the area Sunday or Sunday night, offering the best chance for widespread rainfall between now and early next week.

The amplifying pattern late this week culminates in a potent shortwave advancing thru the Mississippi Valley late Saturday and Sunday, with associated low pressure tracking across the Great Lakes. The major models all depict a cold front trailing that low and sweeping across our area. There remains spread on timing, but it appears likely to reach the TN/NC border Sunday afternoon, if not Sunday night. Instability preceding the front is shown to be low, with ensembles suggesting CAPE is not likely to peak above 500 J/kg. Deep layer shear will be better than at any point in the preceding few days, perhaps 30-40 kt. The best overlap of CAPE and shear would be in our eastern CWA based on current model progs, but not yet seeing a strong overall signal for severe weather potential owing to the meager instability and broad nature of the upper trough. While a narrow band of 1.5" PWAT appears likely to accompany the front, ensemble probs of 1" or more rainfall in 24 hours are low around the fropa.

Temps are expected to return closer to normal Sunday night and/or Monday behind the front, and possibly even below normal in the subsequent day or two.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

At KCLT and elsewhere: VFR conditions expected through the forecast period, with a low-VFR stratocu deck to persist tonight into Tuesday. Light south to southwesterly winds overnight thru Tuesday morning will increase with some low-end gusts expected in the aftn. A few stray showers and possible isolated general thunderstorm are expected to develop in the aftn, but chances still too low to mention at any of the TAF sites. Best chance will be in KAVL.

Outlook: Moisture will increase Wednesday, leading to elevated chances for showers and thunderstorms with associated restrictions thru the rest of the week.

GSP WATCHES/WARNINGS/ADVISORIES

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