Area Forecast Discussion
Issued by NWS Greer, SC

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954 FXUS62 KGSP 221844 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 244 PM EDT Wed May 22 2024 .SYNOPSIS... Temperatures will remain several degrees above normal each day through Tuesday of next week as humid subtropical air remains over the Southeast. Chances for showers and thunderstorms increase Thursday and will remain higher than normal for this time of year into next week as well. && .NEAR TERM /THROUGH THURSDAY/...
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As of 211 PM EDT Wednesday: All quiet across the western Carolinas this afternoon as potent ridging extends from the Mississippi Delta region up into the Carolinas. Observed profiles from our scattering of ACARS sites depict a weak subsidence inversion and, in general, poor lapse rates through the depth of the troposphere; so, no convection has managed to fire off despite decent ~1000 J/kg sbCAPE. Rather, a rapidly-thickening fair-wx cumulus field has developed, but has remained capped. This should continue as the ridge remains more or less stationary over the Southeast this evening. Most of the hi-res guidance fails to produce any convective initiation, even over the mountains; only notable exceptions are the FV3 and NSSL-WRF, both of which tend to run hot under these circumstances (nebulous forcing, moderate capping). So, expect increasing cloud cover, and while a weak shower over the mountains can`t be ruled out, it looks increasingly like a dry day for all. Winds will get increasingly steady out of the SW as we become locked into a weak warm advective/moisture flux regime. Temperatures will soar into the mid- or even upper-80s outside the mountains. Tonight, the ridge will retreat toward the coast, and cirrus will thicken across the western Carolinas. Ripples of weak synoptic forcing will arrive during the predawn hours, but will encounter air too dry to support any precipitation, even over the mountains. Rather, thickening cloud cover will only help to inhibit fog formation in the mountain valleys through daybreak, while keeping lows in the mid-60s, a category warmer than this morning. Rainfall won`t arrive until after 12Z, at which point upper heights will begin falling more quickly and a cold front will sag into the upper Tennessee Valley / Cumberland Plateau. Afternoon profiles tomorrow look much more favorable for convection; the influx of cold air aloft will steepen lapse rates and today`s subsidence inversion will vanish, permitting the development of some 1000-1500 J/kg sbCAPE, perhaps more over the I-77 corridor. Although the environment will be only weakly to moderately sheared (<30kts deep layer, anyway, and with minimal low-level shear)...HRRR and NAM soundings do depict 900-1200 J/kg sbCAPE, especially across the northern Upstate and I-77 corridor. So...downburst winds are a real possibility from any developing updrafts. SPC`s Marginal Risk for Severe Weather, highlighting both wind and hail, looks reasonable enough.
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&& .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
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As of 215 PM Wed: A series of short waves will cross the area with some sort of weak surface feature associated with the waves. This will lead to mainly diurnal convection each day, with some lingering showers possible during the overnight periods. Moderate instability and bulk shear around 40 kts is possible on Friday, along with decent sfc delta Theta-e values. A few severe storms will be possible with some organization. With the good forcing in place, expect widespread to numerous convective coverage of the mountains and foothills and high end scattered coverage elsewhere. Temps will be around 5 degrees above normal. Coverage will not be as widespread on Saturday, but high end moderate instability, along with 20 kts of shear and continued high levels of sfc delta Theta-e values, along with increasing dCAPE may lead to an uptick in severe thunderstorm chances. These would be more of the pulse severe, damaging wind variety. Temps will be around 10 degrees above normal.
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&& .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
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As of 230 PM Wed: Unsettled weather expected into early next week as the series of short waves continue to march across the area. Again, there looks to be weak surface features until Monday when a more organized cold front crosses the area. Expect precip chances to steadily increase Sunday and Monday, although the convection should be mainly diurnal. Some severe storms will be possible again especially if the moderate instability and shear and dCAPE overlap. Temps will be 5 to 10 degrees above normal. Some lingering showers possible Tuesday even as the front moves east, but thunder chances diminish. Temps will be up to 5 degrees above normal. Dry high pressure expected on Wednesday with temps near to slightly above normal.
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&& .AVIATION /19Z WEDNESDAY THROUGH MONDAY/... At KCLT and elsewhere: Another quiet TAF period for most terminals. An extensive cu field has begun to develop across most of the terminal forecast area, and should increase in coverage in the coming hours. However, it should largely remain capped due to robust upper ridging; the hi-res guidance depicts virtually no convective activity this afternoon, even across the mountains, as conditions will simply be too unfavorable for deep moist convection. Any showers that do manage to develop will be weak and short lived, and confined to the NC mountains. At KAVL, confidence was too low for any mention. Tonight, cirrus will thicken across the area ahead of an advancing wave. Isolated shower activity may make it into the mountains after midnight, but will largely fizzle out upon arrival. The increased cloud cover, though, should somewhat hamper fog/low stratus in the mountain valleys, such that KAVL is forecast to remain VFR through the overnight. For KAVL, the first ripples of SHRA/TSRA will arrive during the final few hours of the TAF period, late Thursday morning, and have been handled with a PROB30. Similarly, for KCLT, whose TAF period extends into Thursday evening, a PROB30 was added for the arrival of TS in the I-77 corridor at that time. Outlook: Numerous showers and thunderstorms, along with associated flight restrictions, will continue Thursday night and Friday as a cold front crosses the region. A more active pattern may persist through early next week. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...MPR SHORT TERM...RWH LONG TERM...RWH AVIATION...MPR