Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 220741 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 341 AM EDT Sun May 22 2022 .SYNOPSIS...
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A cold front will approach the region from the west today but won`t finally move across the region until maybe late Monday or early Tuesday. In the mean time, the weather should remain warm and humid because of a weakening Bermuda High. Once the front finally sinks to the south, cooler temperatures are expected for the middle part of the week due to high pressure ridging down from the northeast. A stronger cold front will move in from the west on Thursday and is expected to cross the region on Friday, hopefully providing some much needed widespread rainfall.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 300 AM EDT Sunday: With a longwave ridge axis now well to the east of the Carolinas, strengthening moisture flux has allowed profiles to remain moist in the wake of Saturday`s convection, and widespread cloud cover is observed in satellite imagery across the western Carolinas. Guidance suggests that a weak shortwave will traverse this ridge from around dawn through the early afternoon, dredging up some weak DPVA mainly over the southeastern tier of the CWA, and perhaps resulting in increased cloud cover and even some sprinkles here early Sunday. Otherwise, heights gently fall from Sunday afternoon onward, as a deep trough out over the Midwest begins to encroach on the forecast area. 850 and 700mb charts indicate a frontal passage late in the day on Sunday, which should be enough to trigger some convection across the region in the afternoon and evening. CAMs look tame through mid-afternoon, with sparse coverage of light showers and perhaps a bit of thunder across the area. Destabilization is expected ahead of the front, but with less gusto than on Saturday; absent much synoptic support, midlevel lapse rates look more anemic. So, HREF and SREF are in pretty good agreement on sbCAPE of only 1000-1200 J/kg. Furthermore, lax 850mb flow means poor low-level shear, and even the most aggressive CAMs only produce in the neighborhood of 15kts of deep-layer shear. Consequently, early-afternoon convection looks to be poorly organized and not especially interesting. By early evening, however, the arrival of the cold front will help to focus activity along a narrow band where moisture pools ahead of the boundary. This looks to trigger a line of convection that will sweep across the western Carolinas, and although it`s unlikely to grow upscale into an MCS due to the weakly-sheared environment, activity just along the front will be prone to gusty winds and brief heavy rain. The ARW and NAMnest are in remarkably good agreement that the frontal convergence zone will be near or east of the I-85 corridor by 06z Monday, and fully south and east of the forecast area by daybreak. Profiles look to dry out at least a bit, but winds quickly rebound and become southerly again, limiting the amount of drying likely at least through Monday morning. Cloud cover expected throughout the near term should reduce diurnal temperature variation, with lows near or above climo and highs only a category or two above climo.
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&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
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As of 314 am Sunday: The forecast for the early part of the week is tricky as we undergo a complicated and messy transition to a cold air damming wedge. A short wave riding up and over the eastern upper ridge will keep the cold front in close proximity through Monday...probably draped across the mtns and then along the VA/NC border...warranting a relatively high precip probability as we have that focus for convective development. The guidance moves a large sfc high over the flattened East Coast upper ridge Monday night, sliding it across Ontario to Quebec and into a prime spot to support the development of a cold air damming wedge that should set up early Tuesday morning as the old front slides southward with the cool part of the diurnal cycle. Assuming that happens on that timeline, Tuesday would remain cloudy and cool, perhaps 5-10 degrees below normal in spots, with light precip in the morning and convection developing on the boundary across the srn part of the fcst area. At this time, the amount of rain looks beneficial, and the relatively stable boundary layer across most of the region would preclude severe storms for the most part.
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&& .LONG TERM /WEDNESDAY THROUGH SATURDAY/...
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As of 243 am Sunday: The latter half of the week appears tonight as more of a slow moving target. The new guidance rebuilds the upper ridge off the East Coast more quickly Tuesday night in response to the deepening upper low over the Plains. The net effect will be that our parent sfc high will remain more anchored closer to the New England Coast for longer, which means we will still be dealing with the cold air damming wedge on Wednesday morning, or at least what looks like a stubborn remnant cool pool. The guidance has trended toward a more northwestern track of the Plains upper low and also trended toward lifting it out earlier, which means a renewal of isentropic lift perhaps by Wednesday afternoon. All this makes temps really tricky, which could easily end up 5-10 degrees warmer or cooler than fcst. Strong southerly warm advection should overwhelm the remnant wedge by Thursday morning. Thereafter, paints an optimistic picture with plenty of response to the influx of deep moisture and forcing, so high precip probs are still in order. The guidance has sped up the progression of the front, suggesting that the main threat for severe storms and heavy rain might be Thursday/Thursday night, but confidence in either remains to low to mention. The front should be to our east by the end of Friday. In its wake, expect an upstream ridge to support high pressure through the weekend. Will keep the weekend dry for the time being. Temps will be close to normal for Thursday through Saturday, with a warmup likely by Sunday.
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&& .AVIATION /08Z SUNDAY THROUGH THURSDAY/... At KCLT and elsewhere: Remnant convection has ended across the western Carolinas, with prevailing VFR conditions expected at the TAF sites for the next few hours, gradually degrading to at least MVFR ceilings with some periods of IFR, especially later in the night. Have presently timed the introduction of MVFR ceilings at 08-09z, but low confidence on this timing given lots of disagreement between guidance sources. Not anticipating any visibility issues except in isolated locations in the mountain valleys. Conditions will generally return to VFR after daybreak, as a mixed layer grows and cloud bases rise accordingly. Convection is once again a distinct possibility, with VCSH/VCTS warranted across the region early in the afternoon, then prevailing -SHRA with PROB30s for -TSRA in the evening as a cold front pushes across the NC Piedmont. Timing and intensity of this rain/thunder is still somewhat in question, but generally looks to be better in coverage but lower in intensity compared to Saturday`s convection. Outlook: Diurnal convective chances continue thru much of next week, with associated restrictions possible with any showers or thunderstorms. Nocturnal fog/stratus will be possible as well, especially where rain has recently fallen. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...PM NEAR TERM...MPR SHORT TERM...PM LONG TERM...PM AVIATION...MPR

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