Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 250547 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 147 AM EDT Mon Sep 25 2017 .SYNOPSIS... Broad, dry high pressure will persist across the region through the middle of week. Hurricane Maria is expected to remain off the East Coast through mid-week. A cold front will sweep across the region on Thursday, bringing drier and much cooler air to the area for the end of the week and take Maria out to sea. && .NEAR TERM /THROUGH TODAY/... As of 140 am Monday: A broad upper ridge over the eastern CONUS makes gradual eastward progress as TC Maria moves north. Maria will remain off-shore and her impacts to the GSP area will be limited to some slight enhancement of the northeasterly winds. SCT-BKN high clouds from Maria will persist across much of the region through tomorrow. Subsidence and relatively dry/stable air will yield a pop-less forecast while temperatures will remain 5 degrees or so above climo through the period. && .SHORT TERM /TONIGHT THROUGH WEDNESDAY/... As of 155 PM Sunday: The dry and unseasonably warm weather will persist through the middle of the week, as high amplitude upper ridging persists over the area. A combination of surface high pressure centered over the northeast and Tropical Cyclone Maria moving N toward the NC outer banks will support a sharp surface ridge over the area, with northeasterly surface winds, which could become somewhat breezy by the end of the period. Although moisture may increase to some extent within the circulation around Maria, especially over the Piedmont, showers would be very unlikely with subsidence inversion remaining in place across the area. More likely would be increased high clouds on Tuesday. Therefore, have continued with the dry forecast. Temps 5 to 10 degrees above normal Tuesday rise to around 10 degrees above normal Wednesday. That said, high clouds Tuesday could keep temps across the I-77 corridor a degree or two cooler than forecast. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... As of 145 PM Sunday: For the period starting Wednesday evening, Hurricane Maria is forecast to be just off the North Carolina coast. In the mid to upper flow, a series of strong shortwaves are forecast to cross mid to eastern Canada and Great Lakes region breaking down the upper ridge which has been giving our region much above normal temperatures. The associated cold front crosses our area on Thursday. With very little moisture accompanying the front, only slight chance POPs in the forecast for portions of the mountains. Height falls and cool high pressure will bring temperatures a little below normal next weekend. Hurricane Maria will quickly be shifted east and out to sea once the front encounters the tropical cyclone. A secondary cold front is forecast to cross from the northwest late Friday and Friday night. The combination of this secondary cold front and possible development of a low along the primary front near Florida could bring some rain to mainly southern areas Friday night and Saturday. By Sunday, cool high pressure centered over Illinois will dry and cool weather into the start of next week. Temperatures will start several degrees above normal Thursday then drop to near normal Friday then a few degrees below normal through the weekend. && .AVIATION /06Z MONDAY THROUGH FRIDAY/... At KCLT and elsewhere: The main concern for this period will be the potential for low stratus and/or fog in the mtn valleys and typical cool spots outside the mtns later this morning, meaning that KAVL and KHKY are the only real concerns in this regard. Dewpoint depressions of two degrees at TAF issuance time do give one pause, while light N/NE winds could bring any fog/low stratus developing along the lake over KHKY toward daybreak. Having said that, it`s certainly not a slam dunk that much will develop near these two sites, as the boundary layer is relatively dry, and abundant high clouds may slightly inhibit additional cooling. We did opt to include some mention of restrictions at these two sites, but limited them to MVFR w/in a tempo. Otherwise, VFR conditions are expected through the period. Light NE winds will increase to around 10 kts by late morning, diminishing again this evening. Outlook: Dry conditions expected for the first half of the week. Under mostly clear skies and calm conditions, fog and/or low stratus are possible in the mtn valleys each of the next few mornings. A mostly dry cold front will cross the region late in the week. Confidence Table... 05-11Z 11-17Z 17-23Z 23-00Z KCLT High 100% High 100% High 100% High 100% KGSP High 100% High 100% High 100% High 100% KAVL High 100% High 100% High 100% High 100% KHKY High 100% High 100% High 100% High 100% KGMU High 100% High 100% High 100% High 100% KAND High 100% High 100% 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 && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...JDL/WJM SHORT TERM...RWH LONG TERM...DEO AVIATION...JDL

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