Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 251046 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 646 AM EDT Sun Sep 25 2022 .SYNOPSIS... Scattered showers and isolated thunderstorms are expected today. Dry high pressure builds in through Wednesday with a slow cooling trend. Tropical cyclone Ian moves north into the Gulf of Mexico affecting our weather next weekend. && .NEAR TERM /THROUGH TONIGHT/...
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As of 645 AM...A patch of light rain has entered the western zones over the last couple hours, but is weakening. Otherwise, there is plenty of thick mid clouds and continued mixing to keep temps a little elevated in spots. Definitely starting out warmer than this time yesterday. Only changes with this update were to the aviation grids for the 12z TAFs. An upper long-wave trough will continue to deepen across the Ohio Valley to the Southern Appalachians today, as a series of strong shortwaves ride thru the trough axis. This trough will bring an attendant cold front across the TN Valley this morning, and into the NC mountains this aftn. The digging trough will help increase bulk shear (0-6 km shear in the 50-60 kt range). But the fairly narrow band of deeper moisture will struggle to produce much deep convection as the front pushes into the forecast area. This is thanks to a westerly flow, limiting moisture transport and causing downslope-aided CIN east of the mountains. A lack of good instability seems to be the limiting factor on thunder chances and any severe wx threat. The new Day 1 convective outlook has expanded the marginal risk to include all the NC mountains and adjacent foothills. For what it`s worth, the last few runs of the HRRR have been bringing in 500-800 J/kg of sbCAPE into the mountains, and producing a rather solid line of convection that crosses the northern 2/3rd of the forecast area this aftn, exiting east early this evening. A few damaging wind gusts look possible today, if that verifies. However, the GFS/ECMWF/Canadian have more paltry CAPE, and the other CAMs show much weaker/less organized convection. For now, going with mainly chc PoPs and isolated thunder chcs. Temps will be near normal under partly to mostly cloudy skies. The cold front will exit to our southeast this evening, ushering in drier air and clearing skies. The low-level flow behind the front will not be that strong and generally across the mountain valleys. So mountain valley fog looks likely. Lows will be near normal.
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&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 220 AM EDT Sunday: Quiet weather expected for the short term period as a series of short waves move through the the long wave trough over the eastern CONUS but no significant forcing over our area. Mild and dry high pressure filters in from the north through the period as well. Breezy and dry conditions are expected with a slow cooling trend. Highs will be near to slightly below normal Monday dropping to around 5 degrees below normal for Tuesday. Lows will be around 10 degrees below normal Monday night then a degree or two cooler Tuesday night. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 245 AM EDT Sunday: The upper trough moves east of the area Wednesday with surface high pressure setting up in a cold air damming configuration. The dry forecast continues with highs and lows around 10 degrees below normal. All eyes turn to Ian as it will dominate the rest of the forecast. All of the operations global guidance shows Ian moving north into the weakness in the upper flow behind the departing trough. Questions remain on the exact track as Ian moves from the Gulf, over or near FL, then into the southeastern US. Minor differences in the track could make major changes in the to the observed weather over our area. Therefore, have continued to use the model blend for the forecast. This means a dry Thursday with PoP increasing into the chance range for Friday and Saturday. Highs will be on either side of 10 degrees below normal each day, with lows rising to near normal by the end of the period. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/...
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At KCLT and Elsewhere: A patch of light rain is moving east into the Upstate, but is expected to dissipate before reaching any of the TAF sites. Plenty of mid clouds expected this morning. A cold front will push into the area this aftn, and could trigger scattered SHRA and possibly isolated TSRA. KAVL has the highest chance of some TS, so will add VCTS/PROB30 there. But confidence is still too low for TS at the other TAF sites. But PoPs are high enough to warrant PROB30 for SHRA this aftn, exiting east early evening. Wind should stay SW, with some occasional gusts expected this aftn. Wind will become light this evening and begin to shift from SW to NW toward the end of the 06z TAF period. The mountain valleys may fog up late tonight, so will add some reduced VSBY at KAVL. But not expecting fog elsewhere. Outlook: Dry high pressure will return on Monday and dominate the weather across the region through midweek. Aviation interests will need to monitor the progress of Ian for possible impacts later in the week.
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&& .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...RWH NEAR TERM...ARK SHORT TERM...RWH LONG TERM...RWH AVIATION...ARK

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