Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 201906 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 206 PM EST Mon Nov 20 2017 .SYNOPSIS... Cool high pressure moves off the Carolina coast tonight as a weak cold front approaches from the northwest. This front crosses the area Tuesday night and Wednesday. Low pressure will develop over the Gulf on Thanksgiving Day then cross Florida and up the Atlantic seaboard through Friday. Another strong cold front will arrive over the weekend. && .NEAR TERM /THROUGH TUESDAY/... As of 130 PM EST Monday: Dry high pressure will continue to dominate the area today, but a shortwave trough digging down the MS Valley will continue to push the high offshore this afternoon and tonight. Another fast shortwave diving down out of the northern Rockies tonight will phase with the MS Valley wave, resulting in a high- amplitude trough pushing toward the Appalachians by the end of the period. The approaching front will be mainly dry on the southern end, with most of the dynamics remaining well to the north, but we will be dealing with increasing low-level moisture coming in from the Atlantic and eastern Gulf around the western periphery of the Atlantic high. Isentropic upglide increases across extreme western zones after midnight, and with orographic lift added to this, expect to see increasing clouds and chances for light rain as we push toward sunrise. The clouds will luckily keep temperatures above freezing in areas where moisture will be on the increase, but cannot totally rule out some very light freezing drizzle across the southern mountains as the precip starts. Temperatures tonight should be several (8-10) degrees warmer than they were this morning, but definitely some bust potential there if clouds come in earlier (or later) than expected. Moisture is very shallow and limited to about 850mb and below, with pretty dry airmass above it, so most precip will be in the form of light rain or perhaps even drizzle. Pops were still generally held to low chances and below, but wouldn`t be surprised to see the need for increase pops (but with continued very low QPF). Clouds and moisture/rain will keep temperatures down again tomorrow, 5-8 degrees below normal. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... As of 130 PM Mon: Northwest mid level flow will be in place through the period. This will lead to mainly dry conditions with just a few mainly mountain showers exiting the region Tuesday night. Strong high pressure will build south across the Ohio and Tennessee Valleys while low pressure will form over Florida. The forecast area will be in between these features with the strong high slowly bridging the mountains on Wednesday and Thanksgiving day. Wednesday will be the warmer day of this period with temperatures reaching into the upper 50s to lower 60s in the Piedmont. Expect cooler conditions in the mountains especially the western mountains as colder air slowly pushes into the region. Thursday will be cooler in all areas with highs reaching into the lower to middle 50s in the Piedmont and 40s to lower 50s in the mountains. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 200 PM EST Monday: The medium range fcst period kicks off on Thursday night amidst an amplified upper pattern highlighted by troffing across the east and broad ridging out west. At the surface, weak high pressure will be in place across northeast GA and the Carolinas as cyclogenesis occurs in the GOM beneath a southern stream shortwave impulse and the broader overall trof. Guidance seems to be converging on the on a solution which favors a slower ejecting GOM surface low, which is turn allows for arrival of the next approaching northern stream wave on Friday. Therefore, it looks that the previous non mentionable pops were the right call then, and now, as the arriving northern stream wave picks up the coastal wave. In the meantime, the weak high across the cwfa will slowly slide east allowing for a brief window of wly/swly veered sfc flow ahead of the next trof/front that is set to arrive Saturday night. With that front, strong caa looks favored amidst deep nwly flow bringing yet another cold Canadian airmass into the eastern sector of the CONUS. Guidance favors said nwly flow banking against the high terrain Sunday with some Great Lakes moisture fetching possible. Therefore we could be looking at our first potential advisory level mtn snowfall of the season, however confidence is rather low at this point given the time range. Elsewhere, expecting dry/cold conditions to round of the period with temperatures possibly falling nearly 2 categories below normal levels. && .AVIATION /19Z MONDAY THROUGH SATURDAY/... At KCLT and Elsewhere: VFR this afternoon and tonight with light S winds, occasionally VRB. Cirrus will increase from the W and thicken through the period, then low-level moisture will increase from the S/SW overnight. Expect low VFR cigs to filter into the Upstate around or just before sunrise, with MVFR shortly thereafter, as well as PROB30 for -RA/SHRA. For KCLT/KHKY, MVFR should overspread the area by around 15z. For now, KAVL forecast remains low VFR. Outlook: Low level moisture may keep restrictions and perhaps -RA through Tuesday night. Otherwise, dry/cool conditions should persist into late week. Confidence Table... 17-23Z 23-05Z 05-11Z 11-12Z KCLT High 87% High 100% High 100% High 100% KGSP High 100% High 100% High 100% High 100% KAVL High 94% High 100% High 100% High 100% KHKY High 100% High 100% High 100% Low 58% KGMU High 100% High 100% High 100% High 100% KAND High 94% High 100% High 100% High 83% 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...TDP SHORT TERM...SCW LONG TERM...CDG AVIATION...TDP

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