Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 211046 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 646 AM EDT Mon May 21 2018 .SYNOPSIS... A moist air mass will remain in control of the region through at least Tuesday, bringing a continued high chance of showers and storms each afternoon and evening. A weak front sliding down on Thursday may allow for some brief drying toward the end of the work week, but another round of tropical moisture will lift across the area for the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 325 AM EDT Monday: A few isolated showers still linger across the CWFA as low stratus has developed over much of the region. The mtn valleys have already seen patchy fog develop over the past couple of hours, and additional fog development over the lower terrain is likely if winds can remain light enough. Low temperatures will be well above climatology again this morning as the humid tropical-like airmass remains in place. Otherwise, we aren`t expecting any significant changes to the synoptic pattern thru the near-term, as the upper ridge remains in place over the Southeast. Sfc winds will take on a more SWLY direction this afternoon/evening and then back to a more SLY direction later tonight and early Tues. Still anticipate some convection to fire up over the higher terrain during the early afternoon, however the latest model guidance is not very bullish on convection initiating across the Upstate and Piedmont. This is supported by warmer profiles and weaker lapse rates that should limit sbCAPE despite the high dewpts. As such, I kept chance PoPs throughout the CWFA except near the NC/TN border, where I have likely during the afternoon to early evening hours. High temps should peak a few degrees above normal. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 245 AM EDT Monday: Upper ridge will continue over the western Atlantic and Bahamas to start the short term period, with a subtropical weakness remaining in place across the Deep South. A shortwave crossing the Great Lakes will push a surface trough into and across the Appalachians as we move through the period; the shortwave will phase with the Deep South upper weakness and attempt to start dragging it out of the way. Expect another day of widespread showers and thunderstorms, most numerous across the mountains, on Tuesday, with the added enhancement of upper forcing from the passing shortwave to the north. Lapse rates will remain weak but a little mid-level drying might allow for entrainment of drier air into storms that may increase the potential for gusty winds, but as has been the case the past few days, heavy rain remains the main concern. With the introduction of drier air aloft this will improve PWs somewhat, but really with the warm cloud layer so deep and the tropical profile at least in the lower layers, still expect very efficient rainfall producers. Temps on Tuesday should be bumped down a bit with the widespread cloud cover, a couple of degrees below normal. As we move into Wednesday the surface front will be pushing down the DelMarVa as the upper trough broadens, and while pops will remain, should start to see a decreasing trend compared to Tuesday, with the higher pops across the Upstate and NE GA rather than the mountains. Despite the "front" (in name only) pushing through, temps will increase again to a few degrees above normal with additional sunshine and the downsloping component to the NW winds. && .LONG TERM /THURSDAY THROUGH SUNDAY/... As of 310 AM EDT Monday: We`ll begin the extended in a bit of a lull as a result of the upper trough deepening off the Atlantic Coast, pushing the upper ridge farther south toward Hispaniola but with a large ridge developing over the center of the country as well. As the upper trough deepens and pushes east, the surface front will be forced south, and so while pops do not disappear Thursday into Friday, they are decreased from the high chance/likely pops that have been dominating the area for the past several days. Temperatures will remain above normal and the diurnal nature of the convection will, of course, result in typical "summertime" convective threats. Then things get complicated. No doubt anyone reading this has watched with keen interest the evolution of global model forecasts the past few days with respect to tropical development in the Gulf. Certainly the details with whatever manages to develop simply cannot be nailed down at this time, but all indications are pointing to tropical moisture of some sort lifting into the Southeast/Lower MS Valley on the western side of the upper ridge. Meanwhile another incoming weak shortwave will approach the Great Lakes on Saturday, briefly phasing with the upper tropical low before moving on its merry way and leaving the tropical system to continue to rain out somewhere across the South. Interactions of tropical moisture with synoptic fronts are always problematic. Whatever happens with the tropical system, the problem is that global models are all pointing to a very wet period starting this weekend and going through the end of the forecast period (and later). With fairly wet antecedent conditions, this could be problematic. && .AVIATION /12Z MONDAY THROUGH FRIDAY/...
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At KCLT and elsewhere: A few light showers have persisted over the fcst area since the last TAF issuance with most of them currently located just south of KCLT. A few of these showers could move over KCLT over the next hour or so, but they should not have a significant impact on the prevailing conditions. So far this morning, most sites have been reluctant to fall below VFR, with only KAVL going down and staying down. The other sites could still see a combination of MVFR and IFR restrictions over the next couple of hours, but it`s looking less likely than previously thought. Otherwise, today looks similar to yesterday with mountain convection beginning in the early afternoon and possibly spreading into the foothills and piedmont. Winds should remain light to calm thru the morning, and pick up from the SW during the afternoon. By Tuesday morning, they should back to a more SLY direction. Outlook: The persistent unsettled pattern will continue through midweek, with flight restrictions possible each day under isolated to scattered showers and thunderstorms. Confidence Table... 10-16Z 16-22Z 22-04Z 04-06Z KCLT High 83% High 100% High 100% High 100% KGSP High 83% High 100% High 100% High 100% KAVL Low 47% High 100% High 100% High 100% KHKY Med 78% High 100% High 100% High 100% KGMU Med 61% High 100% High 100% High 100% KAND Low 47% 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
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&& .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...TDP NEAR TERM...JPT SHORT TERM...TDP LONG TERM...TDP AVIATION...JPT

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