Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 250130 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 930 PM EDT Thu May 24 2018 .SYNOPSIS... High pressure will remain over the mid-Atlantic states tonight, then moves offshore Friday. A tropical low in the Gulf of Mexico will move ashore and wobble over the lower Mississippi through the holiday weekend. Tropical moisture will stream northward into the region through the holiday weekend, giving the area a good chance for scattered afternoon and evening showers and thunderstorms. && .NEAR TERM /THROUGH FRIDAY/... As of 930 PM EDT Thursday... Did not see any showers or thunder in the southwest portion of forecast area as previously forecast. After losing diurnal heating, not a lot of confidence that anything will develop, but small possibilities exist for something to advect up from the south. Short range guidance continues to hint at the possibility so leaving low PoPs for these areas at this time. Otherwise, adjusted temps and DPs to match current obs and trends with no other notable adjustments. Previous Discussion... Weak high pressure will remain wedged across the Blue Ridge east into the piedmont through tonight. A weak inverted trough sits along the western side of the Appalachains from the Tennessee Valley north into the coal fields of West Virginia. This trough with ample heating and in the vicinity of a wedge boundary, may spark a few showers or storms this afternoon and evening. There is some downsloping that could limit convection, but it is weak, therefore kept pops in the low chance/scattered range from the North Carolina High Country to the Mountain Empire of southwest Virginia. High pressure will keep the rest of the area dry with lower dewpoints mainly north of a Bluefield to Danville line. Tonight, not much change from previous forecast, models hinting at the low threat of showers in the NC mountains/foothills, with a better threat of patchy fog to the northeast as maritime air continues to move in from the east/southeast. Models keeping skies fairly clear north of the NC/VA border so will see if any stratus forms, as NAM forecast soundings suggest this potential along/east of the Blue Ridge. Lows tonight will be in the 50s in the mountains, with upper 50s to lower 60s east. The wedge erodes Friday which will allow warm moist southerly flow to increase over the region. As inversion break by the afternoon, scattered showers and thunderstorms are possible across the mountains in the afternoon. With ridging aloft, storms` life cycle may be limited to 30-60 minutes. Temperatures Friday afternoon will warm into the 70s across the mountains to lower to mid 80s east. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/... As of 115 PM EDT Thursday... A vorticity maximum was trapped under the southeast upper ridge will drift across the southern Appalachians on Saturday. Not much forcing with this feature but may still trigger afternoon and evening thunderstorms along the southern Blue Ridge. 500 MB heights remain above 582dm and resulting in above normal temperatures. GFS lined deeper moisture up across Virginia and Tennessee on Saturday and from Delaware to southern Kentucky on Sunday. No well defined surface boundaries or upper support but enough heating each day for isolated to scattered afternoon and evening thunderstorms. Surface dewpoint approaching 70 degrees too by Saturday afternoon so humid during the day with most unstable Convective Available Potential Energy roughly around 2000 J/KG and muggy at night. Thunderstorms may have the potential for heavy rain on Saturday with storm motion from 10 to 20 mph and precipitable water values of 1.5 to 1.8 inches. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 115 PM EDT Thursday Models bring moisture and lift into southern Virginia and northern North Carolina on Monday. Will have a higher probability of rain for the afternoon and evening. Monday and Tuesday will have upslope southeast wind and precipitable water values around 1.5 inches so all that moisture will mean the potential for heavy rain. Potential tropical system will remain near the Gulf Coast Monday through Wednesday between upper ridge over the southwest then central United States and the off the southeast coast. Thursday the low opens and fills and moves northeast. Models have come into better agreement taking this feature into the Tennessee Valley by Thursday morning. ECMWF has the deeper moisture over Virginia and North Carolina again Wednesday and Thursday. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/... As of 725 PM EDT Thursday... VFR conditions exist through most of the forecast area with some MVFR ceilings noted through the mountain empire of VA and the Northwest mountains of NC. These lower ceilings should begin to erode in the next couple of hours after they lose their diurnal support. As it stands, visible satellite give no indication that these lower clouds will advect over any of the TAF locations. DPs remain rather high and with sufficient clearing tonight will maintain a low chance for MVFR fog overnight. Will not advertise fog at ROA and BLF as they do not appear as likely to reach the crossover temp overnight. Fog dissipates shortly after sunrise and conditions will be VFR throughout as high pressure remains the main player for the duration of the forecast period. Friday afternoon, isolated showers and thunderstorms will be possible through the mountains. Due to the isolated nature and the short life expectancy of these storms have opted not to specifically include in any TAF for now, but can likely be handled best with TEMPO groups in future TAF runs. Confidence high in cigs and winds thru the period, medium on vsbys. .Extended Aviation Discussion... VFR Friday night. Tropical like moisture streams back north as a warm front moves through Saturday with a return to showers/storms and potential sub-VFR conditions and heavy rain thru the holiday weekend. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RCS NEAR TERM...JR/RCS SHORT TERM...AMS LONG TERM...AMS AVIATION...JR/RCS is the U.S. government's official web portal to all federal, state and local government web resources and services.