Area Forecast Discussion
Issued by NWS Blacksburg, VA

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242 FXUS61 KRNK 270615 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 215 AM EDT Thu Apr 27 2017 .SYNOPSIS... High pressure will build across the southeastern United States resulting in a considerable boost to the temperature with above seasonal warmth expected by the weekend. An increase in southwesterly wind flow will bring enough moisture back into the area by late Thursday to promote widely scattered afternoon and evening showers and thundershowers over the mountains. && .NEAR TERM /THROUGH TODAY/... As of 710 PM EDT Wednesday... With low pressure off the middle Atlantic coast pulling away and some ridging aloft, expect quiet weather to prevail through tonight. Believe there is enough ground moisture from recent rainfall to help moisten the boundary layer and generate some patchy valley fog toward daybreak. For Thursday, despite most energy guidance is becoming a bit more enthusiastic and faster with the cold front approaching from the west tomorrow. Precipitation will hold off until the afternoon and there looks to be enough instability and some shear to support some stronger storms/clusters. Have bumped POPs up to high chance/likely to reflect this thinking. && .SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/... As of 410 PM EDT Wednesday... Unseasonably warm, summerlike weather expected with the potential for showers and thunderstorms especially along and west of the Blue Ridge Mountains heading into the latter part of the week. Showers and thunderstorms will move east across the region Thursday afternoon into Thursday evening. Partly cloudy conditions will prevail Thursday night into Friday morning. Low temperatures Thursday night will range from the mid 50s in the mountains to the 60s in the Piedmont. Friday and Saturday feature the re-establishment of an amplified mid- level ridge across a large part of the Southeastern CONUS. Meanwhile, a mid-level trough will dig and deepen over the Four Corners Region. The closed low will slowly edge northeast towards the plains this weekend. A surface low develops in Texas Friday and travels northeast into Saturday night. A warm front extends eastward from the low center in the Ohio Valley, followed by cold front trailing south. The frontal boundaries will serve as a trigger for showers and thunderstorms. On Friday, the air mass in low-levels is relatively capped, progged instability aloft is around -2 to -4 Showalter indices and MUCAPES in excess of 1000 J/kg. This supports isolated showers and thunderstorms Friday afternoon into Friday evening mainly from the Blue Ridge west. High temperatures on Friday will climb into the mid 70s in the mountains to the mid 80s in the Piedmont. Any convection will taper off quickly Friday night. It will be a mild night with readings from mid 50s in the mountains to the mid 60s in the Piedmont. As the low center lifts northward Saturday, the combination of heating and an unstable airmass will create a few showers and thunderstorms along and west of the Blue Ridge. High temperatures Saturday will moderate to around 80 degrees in the mountains to around 90 degrees in Piedmont. It will be mild Saturday night with lows generally from around 60 in the west to the upper 60s in the east. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 410 PM EDT Wednesday... Very warm and humid conditions continue Sunday with the chance for showers and thunderstorms, especially along the Blue Ridge. By Monday, the vertically stacked upper closed low over the Midwest will move into the Great Lakes region. This will push a vigorous cold front into the area from the west with a good chance of showers and thunderstorms through Monday afternoon into Monday night. High pressure will then build on for Tuesday with cooler weather and windy conditions. Moisture increases on Wednesday, with better chances of rain Wednesday night into Thursday. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... As of 210 AM EDT Thursday... Clear skies will promote good radiational cooling early this morning with ambient ground moisture from recent rainfall leading to some patchy valley (MVFR) fog, otherwise expecting widespread VFR conditions all sites through 18z/2PM Thursday before frontal showers and a few storms arrive along the western slopes of the Appalachians. Increasing clouds/showers are the result of an approaching cold front. Ongoing line of deep convection over the TN valley is forecast to weaken this morning before redeveloping along the outflow boundary as it moves into the western Appalachians this afternoon. Storm coverage the afternoon is expected to be scattered in nature...thunderstorm clusters as opposed to a solid line. Southerly winds will become a bit gusty from mid morning on per 35 to 40 knot LLJ ahead of the approaching front. Showers/Storms are forecast to linger until loss of daytime heating. The actual surface front is expected to wash out and dissipate as it crosses the mountains, so in spite of a wind shift as it crosses the mountains this evening, very little if any wind shift is expected over the piedmont east of the mountains where the winds will remain predominantly out of the south or southwest. Extended Aviation Discussion... Mainly VFR flying weather is expected for Friday and into the weekend as high pressure builds over the southeast states promoting temperatures which will be much above normal. Warming surface temperatures also means increasing atmospheric instability. As such, potential will exist for cloud build-ups and the risk for isolated to scattered thunderstorms along the spine of the Appalachians during the peak heating hours each afternoon. && .HYDROLOGY... As of 525 PM EDT Wednesday... Flood warnings continues for the Dan and Roanoke Rivers The Dan River has crested and is falling at Danville, and has crested at Paces. At South Boston the river is slowly rising and should crest after midnight tonight. The Roanoke River at Randolph has crested and will begin falling this evening. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PM NEAR TERM...MBS/RCS SHORT TERM...KK LONG TERM...KK AVIATION...PM HYDROLOGY...

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