Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 250230 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 1030 PM EDT Sat Sep 24 2016 .SYNOPSIS... A broad upper ridge and surface high pressure will remain in place over the southeast through tonight, then break down Sunday as an upper trough approaches from the Mississippi Valley. A slightly cooler and moist airmass will begin Sunday as a frontal boundary settles into the area from the north. Unsettled weather is likely to linger through the first half of next week before drier and cooler air enters behind the passing cold front by the middle of next week. && .NEAR TERM /THROUGH SUNDAY/...
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As of 1030 PM: Recent satellite images indicated a few patches of clouds across the NC foothills and mtns. I will update the forecast to adjust sky cover to satellite data. Otherwise, the current forecast appears to be in good shape. As of 745 PM: Light winds with thin high clouds expected across the western Carolinas through much of tonight. During the pre dawn hours, NAM indicates that the nose of sfc ridging and backdoor cold front will push SW across VA, reaching the I-40 corridor by sunrise. Near and behind the leading edge of the cold front should be the favored area for stratus to form. Otherwise, the CWA should see a wind shift from the NE within one to two hours following sunrise. During late Sunday afternoon, the backdoor cold front is forecast to push across the upstate of SC into the upper Savannah River Valley. The timing of the front should result in the overlap of weakest CIN and highest CAPE. I will increase the mention of TSRA along and ahead of the front. As of 510 PM: KGSP radar indicated a few showers across the western NC mtn counties. I will update the forecast to increase PoPs to schc under the showers through 23z. Otherwise, I will keep temps nearly steady over the next hour, then diurnal cooling through the evening. KAVL tied todays high temperature of 89 set in 1895. Previous discussion... Areas of few-sct cu and maybe a small sw nc ridgetop shower will dissipate with loss of htg early this evening. Still expecting a back door cold front to approach from the north tonight with an accompanying wind shift back to NE and an associated stratocu field across western NC during the late night hours. The southward push of said boundary is expected to slow on Sunday, as it becomes parallel to the upper flow. This may serve as a focus for scattered deeper convection during the afternoon along with scattered activity in the favored terrain-aided locales. With the push of lower thickness values into the northern cwfa, and the potential for cloudy skies to start off the day on Sunday, maximum temperatures are slated to be 10-12 deg f cooler than today along I-40, but will be close to persistence on the warm side of the front, acrs the far sw cwfa.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... As of 235 PM EDT Saturday: Back door cold front remains stalled across the area Sunday night with high pressure weakly ridged into the area from the NE. With a moist low level southerly flow in place, expect scattered showers to remain over the area through the night. Any storms should be pushed southeast toward the frontal boundary. Lows will be around 10 degrees above normal. The front will wash out on Monday as a cold front moves to the spine of the Appalachians and into the area Monday night. The moist low level southerly flow continues through both periods. Expect at least good coverage of showers across the area with scattered thunderstorms as moderate instability develops. Even with the front, shear remains light, so severe chances are minimal. However, there should be some beneficial rainfall with the convection as QPF forecasts are up to half an inch across the mountains and foothills. Highs Monday will be cooler "only" up to 5 degrees above normal. Lows Monday night will be 5 to 10 degrees above normal. The guidance shows a little timing difference on the speed of the cold front moving through the area on Tuesday. Best chance of precipitation will be outside of the mountains with any solution. That said, scattered convection is expected during the morning even where chances are lower. Instability should remain weak, but high enough for scattered thunderstorms, especially outside of the mountains. Highs will be near normal mountains and a couple of degrees above elsewhere. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... As of 150 PM EDT Saturday: We begin the medium range/extended with a change in airmass Tuesday night as the cold front moves east and away from the Interstate 85 corridor toward the coast. The forecast deep closed upper low will be centered over the Great Lakes Tuesday night. The ECMWF has this low centered over the western Carolinas Thursday night. The GFS on the other hand has this low opening up with the westerly flow Wednesday night and moving the trough east and off the east coast by Thursday night. We will be keeping the medium range forecast dry after the few departing showers early Wednesday. At this time do not believe the closed low will wobble this far south along there is a possibility that the closed low will become detached from the westerlies and wobble around for a few days. Temperatures will be near normal Wednesday then about a category below normal Thursday through Saturday. && .AVIATION /03Z SUNDAY THROUGH THURSDAY/...
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At KCLT and elsewhere: Light winds with thin high clouds expected across the western Carolinas through much of tonight. During the pre dawn hours, NAM indicates that the nose of sfc ridging and backdoor cold front will push SW across VA, reaching the I-40 corridor by sunrise. Near and behind the leading edge of the cold front should be the favored area for stratus to form. I will indicate SCT IFR level stratus at KHKY by the mid morning hours. Otherwise, terminals should see a wind shift from the NE within one to two hours following sunrise. During late Sunday afternoon, the backdoor cold front is forecast to push across the upstate of SC into the upper Savannah River Valley. The timing of the front should result in the overlap of weakest CIN and highest CAPE. I will add a PROB30 for KGMU, KAND, and KAVL for -TSRA between 21z to 24z. Outlook: A back door cold front will push into the region on Sunday, bringing increased moisture for early next week. Another cold front will push in from the west on Tuesday, bringing the best chance for showers and possibly some TSTMS. Then dry high pressure returns midweek. Confidence Table... 02-08Z 08-14Z 14-20Z 20-00Z KCLT High 100% High 100% High 89% High 91% KGSP High 100% High 100% High 100% High 100% KAVL High 100% High 91% High 100% High 100% KHKY High 100% High 98% Med 69% High 100% KGMU High 100% High 100% High 100% High 100% KAND High 100% High 87% High 100% High 100% The percentage reflects the number of guidance members agreeing with the scheduled TAF issuance flight rule category. Complete hourly experimental aviation forecast consistency tables and ensemble forecasts are available at the following link: www.weather.gov/gsp/aviation
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&& .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...NED SHORT TERM...RWH LONG TERM...DEO AVIATION...NED

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