Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 312125 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 525 PM EDT Tue Mar 31 2020 .SYNOPSIS... A low pressure center moves east and off the Carolina coast tonight. Canadian high pressure slowly builds into the region through Friday. A weak cold front moves through on Sunday. && .NEAR TERM /THROUGH WEDNESDAY/... As of 515 PM Tuesday: precip has ended across most of the fcst area over the past few hours, with just some lingering light showers over our far eastern zones and the wrap-around precip over the NC/Tenn border region. Cigs also remain VFR across most sites with a thick stratus deck in the 4 to 6kft range covering most of the CWFA. I still expect another round of light showers late tonight and into the overnight, however coverage appears to be trending downward with each new run of the CAMs/mesoscale models. Otherwise, low pressure is set to pass just south of the CWA early this evening, supported by a shortwave trough moving east across the lower Ohio Valley. A relatively dry sfc airmass remains in place across Virginia and the Carolinas. Warm upglide did produce very light precip into this airmass earlier today, but not apparently enough so to lock in CAD as previously expected. A second round of precip should occur this evening as the shortwave itself drifts overhead. Confidence is not particularly high in the temp/dewpt/sky fcsts through tonight east of the mountains. Temps are currently fcst to fall near normal in the Piedmont, but likely won`t fall as much if the clouds are more stubborn than fcst, due to the wedge. Ah, yes, the mountains. What a story. With the moistening aloft having not been as quick as expected, that left an opportunity for the heavier precip to diabatically cool the midlevels, which resulted in some high-elevation snow and sleet already today. Temps at the higher elevations will remain cool enough for some wintry mix into early evening, when they begin to really drop with CAA behind the shortwave; the event turns to NW Flow at that time too. Snow ratios won`t be all that good assuming the moist layer is as shallow as depicted on prog soundings, but the upslope enhancement should produce modest totals at the highest elevations, where temps are cold enough the longest. Locations above 5000 ft likely will see more than 2 inches total, but that area is too small for an advisory. We will issue a Special Wx Statement to cover the threat. The NW flow snowfall should taper off gradually thru the morning. Except perhaps for some diurnal cu trapped under a low inversion, skies will clear out across the Piedmont. However, max temps still look to be 7 to 10 degrees below climo in that area, and under continued CAA the high elevations may struggle to get into the lower 40s. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... As of 100 PM EDT Tuesday: After the cold front/low pressure system clears the area by the start of the short term period 00Z Thursday, a generally quiet pattern will return. Surface high pressure centered over the Great Lakes will slide southward on Thursday and Friday before moving off the east coast. Upper heights will rise just a bit both days as a low-amplitude upper ridge moves towards the east coast, with max and min temps rebounding to right around average by Friday afternoon. Temps Thursday morning will be just below freezing in the high peaks and in the mid 30s for most mountain zones, but will remain in the high 30s to low 40s elsewhere. Enough of a N/NErly breeze is expected through Thursday morning that frost shouldn`t be an issue in any active frost/freeze zones. Lows Thursday night/Friday morning will increase to near normal, so no frost/freeze concerns anticipated. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... As of 145 PM EDT Tuesday: The medium range picks up Friday night with the area still under the influence of weak surface high pressure and muted ridging aloft. Saturday should remain dry as well before a weak upper shortwave and surface front cross the forecast area Saturday night. Current model guidance actually indicates very little in the way of available moisture on Saturday night, so only slight chance to low-end pops were introduced. A frontal boundary may activate over the area Sunday and increase rain chances, but deep moisture and forcing are somewhat lacking, so just chance pops were added Sunday. A more substantial shortwave will move across the area Monday into Tuesday, with a better chance for more widespread rainfall early next week. The pattern just beyond the end of the medium range will remain unsettled. Upper ridging over the eastern CONUS will keep max and min temps about 5 degrees above average through early next week. && .AVIATION /22Z TUESDAY THROUGH SUNDAY/... At KCLT and Elsewhere: Confidence low in this set of TAFs given poor performance of guidance so far today, with quasi-CAD event yet to really unfold. Precip did develop on the warm side of a fast-moving low pressure system, but it has had trouble really locking in the wedge airmass, which was expected to produce widespread IFR this afternoon. Current expectation is that cigs will mostly stay VFR until next round of precip arrives late this aftn and evening beneath upper shortwave. That still likely will cause most of the area to drop to IFR for a portion of the night as CAD finally develops, with drier and colder air scouring that out later in the night. The remainder of the period will see SCT-BKN low VFR stratocu. Winds will be mainly in the NE quadrant across the Piedmont this aftn (SE at KAVL), backing to NW tonight following the wedge. Some gustiness will occur at times. The higher terrain near the Tenn border will see rain and snow showers late this afternoon through early Wednesday within NW flow, but these do not look likely to affect KAVL except perhaps to generate an occasional MVFR-level cloud deck. Outlook: VFR will return with dry high pressure on Wednesday and Thursday, possibly lasting through the weekend, though return flow ahead of the next system may bring nighttime and early morning restrictions to parts of the area Saturday night. Confidence Table... 21-03z 03-09Z 09-15Z 15-18Z KCLT Med 70% Low 56% High 96% High 100% KGSP Med 68% High 81% High 100% High 100% KAVL Med 71% Med 78% High 86% Med 74% KHKY Med 75% Med 68% High 100% High 100% KGMU Med 68% High 93% High 100% High 100% KAND High 90% High 93% 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 are available at the following link: && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...JPT/08 SHORT TERM...17 LONG TERM...17 AVIATION...JPT/08 is the U.S. government's official web portal to all federal, state and local government web resources and services.