textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated PoP this evening for northern Blue Ridge showers.

The aviation discussion was updated for the 00z TAF issuance.

KEY MESSAGES

1. Warming temperature trend continues today with isolated to widely scattered showers possible. Better shower and thunderstorm chances on Wednesday. 2. Daily chances for showers and thunderstorms continue Thursday through Saturday, with temperatures remaining well above normal. 3. Cold front Sunday brings a chance for more appreciable rainfall followed by cooler conditions early next week.

DISCUSSION

Key message 1: Warming temperature trend continues today with isolated to widely scattered showers possible. Better shower and thunderstorm chances on Wednesday.

Extended southeast ridging and continued south to southwesterly flow will aid in a warming trend starting today and Wednesday. Better moisture advection will help to kick off isolated showers today with afternoon highs reaching into the upper 70s and lower 80s. Best chance for a shower or thunderstorm will be over the mountains. Lingering stratus is expected overnight with lows in the upper 50s and lower 60s (mid 50s across the higher elevations).

Another day in the warm and moist airmass will allow for deeper destabilization on Wednesday. CAMs continue to show better coverage of convection during peak heating as CAPE values rise. Better convective chances are expected, especially across the mountains due to better access to a trigger mechanism. Afternoon highs are forecast to be in the low to mid 80s.

Key message 2: Daily chances for showers and thunderstorms continue Thursday through Saturday, with temperatures remaining well above normal.

Bermuda high remains strong in the second half of the week, extending over the Southeast states. Models remain pretty consistent in showing dry midlevel air advecting inland Thursday, seemingly originating via strong subsidence under the offshore ridge. This has a suppressing effect on convection Thursday such that precip chances trend lower briefly, though isolated or widely scattered coverage still is possible that afternoon over the mountains. Flow backs to SE which still appears to bring the sea breeze front into the area, however, increasing low-level moisture Thu night. Meanwhile, on the periphery of the high, a sfc/upper low tracks into the Great Lakes Thursday night. 850-700mb flow veers to SW'ly again over the area in response, and midlevel moisture increases. These changes could result in very light precip developing early Friday morning over the southern CWA, but perhaps more notably make vertical profiles more favorable for diurnal convection Friday. PoPs thus trend higher once again that afternoon with the mountains having better chances as usual. Some very light showers could continue overnight into Saturday morning in our southwestern zones with some degree of WAA continuing in low levels, and weak elevated instability. Diurnal convective potential appears similar Saturday compared to Friday. Despite the moisture aloft, without strong forcing and only modest CAPE values generally peaking below 500 J/kg, rainfall is not likely to be enough at any one location to improve drought conditions. Higher minimum relative humidity values should however help mitigate critical fire weather conditions to some degree.

Both morning mins and afternoon maxes remain on the order of 10-15 above normal in the Thu-Sat period.

Key message 3: Cold front Sunday brings a chance for more appreciable rainfall followed by cooler conditions early next week.

Models depict a cutoff low tracking thru the Great Lakes Saturday night and Sunday, which still looks to pull a cold front across the southern Appalachians Sunday. While the best dynamic forcing is still depicted as remaining well to our north, some DPVA is progged to accompany the front into the area. A narrow zone of 1.4" to 1.5" PWAT also is noted along it. Lapse rates are relatively weak, though, and given the current expected timing, the greatest potential for afternoon destabilization is to our east. Therefore, despite improving shear, the potential for severe weather appears minimal due to the lack of instability. Model QPF would not be remarkable were our antecedent conditions not so dry. LREF 75th percentile is not even an inch in the western NC mountains, where downslope effects are least likely to reduce precip potential, and not even a half inch in the I-77 corridor. Nonetheless this currently looks the best shot at widespread accumulating precip through the forecast period, and through the first half of next week for that matter. Dry continental high pressure will build in behind the front Sunday night, bringing temperatures back to around normal, or even a little below, Sunday night through Tuesday. Low afternoon relative humidity is likely to return Monday and Tuesday which could be an important consideration for fire weather, particularly where rainfall ends up insignificant through Sunday.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

At KCLT and elsewhere: VFR conditions expected through the TAF period at all terminals. Some low VFR stratocu will linger through the night with increasing mid or high clouds. Low VFR Cu develops during the day Wednesday with BKN mid or high clouds. Better chance of afternoon convection on Wed but favors the western sites. Have PROB30s for all but KCLT where the chance is lower. S to SW winds may keep some low end gusts early this evening then diminish through the night. S to SW wind picks back up during the day with low end gusts possible.

Outlook: Daily chances for showers and thunderstorms with associated restrictions through the weekend.

GSP WATCHES/WARNINGS/ADVISORIES

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