Sunrise 6:13 AM   Sunset 8:30 PM Moonrise 5:55 PM   Moonset 3:51 AM

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FXUS62 KGSP 211817 AFDGSP

Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 217 PM EDT Tue May 21 2024

SYNOPSIS
Warm high pressure will persist across the region through the middle of the week with a few showers and storms possible each afternoon over the mountains. Rain chances increase Thursday and remain in the forecast each day through Tuesday. Several weak waves of low pressure will move from the lower Mississippi Valley to the Carolinas. Temperatures will remain above normal.

NEAR TERM /THROUGH WEDNESDAY/
As of 155 PM EDT Tuesday: All quiet across the area as a potent positively-tilted ridge extends from the western Gulf Coast all the way into the Mid-Atlantic. Despite the intrusion of a weak wave into this upper pattern, there's no evidence yet of any convective towers going up over the NC mountains. The latest analysis puts some 500-1000 J/kg sbCAPE across the NC-TN border counties, though, so eventually we should see at least some weak showers start to develop. Most of the CAMs depict at least some widely scattered ridgetop convection ramping up over the next 2-3 hours. Temperatures should climb into the mid-80s

Tonight, profiles will dry out as the wave translates east.
The mountains may experience some debris cloudiness even after convection subsides, but will clear gradually after midnight as the upper height gradient strengthens a bit, and residual moisture is advected away. A few hours of mountain stratus and valley fog are depicted in most of the guidance, to clear out again quickly after daybreak Wednesday. Lows will drop to the lower 60s across most of the area. Another day of generally suppressed weather is expected on Wednesday. The lack of any discernible synoptic triggering mechanism paired with lapse rates at least as poor as today's should preclude much, if any, convection from occurring; instead, we can expect a dry and quiet day tomorrow.

SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/
As of 145 PM Tue: A series of short waves will cross the area in generally westerly flow aloft. This will bring increasing chances of mainly diurnal convection Thursday and Friday. That said, showers may linger overnight, especially across the mountains. Instability may rise into the moderate range Thursday, but a weakening warm nose may linger keeping the better instability over the mountains, and possibly into the I-85 corridor, especially if the forcing overcomes the warm nose. Bulk shear will approach 50 knots, so a severe storm or two will be possible if the instability and shear can overlap.
Temps will be around 5 degrees above normal.

Looks to be a better chance of realizing moderate sbCAPE Friday as the warm nose appears to fully erode. Bulk shear drops back to around 40 knots, but a few severe storms will be possible again given the forcing and dCAPE values. Temps remain nearly steady.

LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/
As of 215 PM Tue: The active pattern continues as short waves move through the generally westerly flow and across the area. With the strongest wave moving in on Tuesday. This will least to continued chances of diurnal convection, with lingering nocturnal showers as weak surface features move through in association with the waves.
Too soon to tell if any of the days have a better severe storm chance than the others, but they are possible. Also, heavy rainfall chances will steadily increase as PW values increase with each wave.
Isolated flooding would be possible in areas that receive rounds of heavy rainfall.

AVIATION /18Z TUESDAY THROUGH SUNDAY/
At KCLT and elsewhere: VFR through the period for non-mountain terminals, as upper ridging suppresses widespread convective activity. CAMs depict some isolated convection across the mountains today, which like yesterday will be mainly showers. Can't rule out some TS, but it's looking isolated enough to forego mention in even the KAVL TAF. This was left a PROB30 as confidence still isn't great on initiation, which is lagging behind most of the CAMs at this time (c. 1715z). Tonight, some MVFR fog/ceilings are expected in the major mountain valleys, with impacts only for KAVL.
More of the same tomorrow, with VFR conditions after daybreak and isolated ridgetop convection in the afternoon..

Outlook: More numerous showers and thunderstorms, along with associated flight restrictions, will return with a cold front late Thursday into Friday. A more active pattern may persist into the weekend.

GSP WATCHES/WARNINGS/ADVISORIES
GA...None.
NC...None.
SC...None.

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