Area Forecast Discussion
Issued by NWS Blacksburg, VA

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276 FXUS61 KRNK 211802 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 202 PM EDT Sun Aug 21 2016 .SYNOPSIS... Scattered showers and thunderstorms today ahead of an approaching cold front which will bring cooler and drier air to the region. High pressure will dominate the weather until mid-week. && .NEAR TERM /THROUGH TONIGHT/... As of 1255 PM EDT Sunday... For this afternoon, a nearly solid line of showers will continue heading eastward across the region. No thunderstorms have occurred yet, but chances will increase as the activity moves into more unstable air in the east. No major changes made to the ongoing forecast. As of 1015 AM EDT Sunday... Forecast update this morning will see its biggest changes across the eastern portions of the area. Have removed the isolated to chance POPs across this region of the area, especially across the southeast portion of the area, until the early to middle afternoon. This adjustment was based upon the latest radar and guidance trends. Have also increased the high temperatures in this area by a degree or two with the later arrival of notable precipitation. As of 345 AM EDT Sunday... Upper trough will rotate across the Great Lakes today with associated cold front pushing from the eastern Ohio Valley at midday through to the Atlantic coast by early evening. Should see a period of showers and possibly a few embedded thunderstorms ahead of and along the boundary today with the best chances for rain in the west and best chances for thunder in the east although will maintain some thunder in the grids as MU Capes briefly reach 500-1500 J/kg from west to east across the CWA in the 12-21z time frame across the CWA per NCEP SREF. SPC maintaining marginal risk in the far eastern counties with that higher CAPE and it may depend on the amount of sun in that area. Best shear will be north of the RNK CWA so any severe threat will be isolated. Rainfall amounts in the 0.25 to 0.75 inch range today seem most probable as the front will make fairly rapid progress with the strong upper support. Rain should be tapering off by around 00z/22 with lingering showers in the far east possible after that time. Don`t anticipate any significant hydro issues with the speed of movement although high PWATS ahead of the front will allow for some pockets of heavy rainfall. After the front much drier air will work into the region which may be a welcome change for some from the remarkably persistent near tropical air mass of recent weeks. Should see lows into upper 50s west to mid- 60s east by Monday morning, the coolest we have seen since about one month ago. And actually those temps are about normal for this date in August which shows how long we have been above normal at night, over 30 days. && .SHORT TERM /MONDAY THROUGH WEDNESDAY/... As of 330 AM EDT Sunday... Dry cool air will filter into the region Monday as high pressure will be centered over the Ohio Valley. With zonal flow aloft, this high pressure system will drift east over the Appalachian Mountains Monday night, then wedges down the Mid Atlantic on Tuesday. The pattern remains progressive on Wednesday with the wedge center moving off the New England Coast. While this ridge is in the forecast area, temperatures will remain cooler than normal with the mountains being in the 70s and areas east of the Blue Ridge in the low to mid 80s. Humidity levels each day will stay below 50% but will increase on Wednesday as winds become southeasterly. Also with a very dry air in the region, there will not be any showers or thunderstorms in the area until late in the week. && .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/... As of 345 PM EDT Saturday... By Thursday, the surface high continues to drift off shore allowing better return of Gulf moisture into the region. A broad trough in the central U.S. will help drive a weak cold front toward the region late Thursday with a better chance of convection as a result west of the Blue Ridge. The front will continue to move southeast Friday toward the NC Piedmont, then wash out as high pressure aloft once again intensifies across the region. Dynamics are weak both days, but scattered convection can be expected, especially across the mountains, mainly west of the Blue Ridge Thursday, then more to the east of the Blue Ridge across the Piedmont on Friday. Temperatures and humidity levels will be on the increase again during this period as PWATS surge back toward the 2.0 inch mark and 850mb temps creep back toward +20C. The pattern established during the extended period opens the door to potential tropical activity that may be looming the future. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... As of 150 PM EDT Sunday... A cold front will move through the area this afternoon and early evening. Anticipate scattered showers and a few thunderstorms with its passage. The greatest concentration of storms will be along and east of a KLYH-KMTV line. Most areas east of the Blue Ridge will remain VFR except for brief moments under heavier showers or thunderstorms. The mountains will have areas of IFR/MVFR ceilings within the area of showers. Limited if any thunderstorms are expected in this region. Visibilities will also drop to MVFR or brief IFR levels under the areas of heavier precipitation. The front is expected to be through the region by the early evening. Look for skies to clear in areas mainly east of the Blue Ridge. Lingering low level moisture and a developing northwest flow behind the front will help maintain a IFR/LIFR ceiling across western parts of the region where the impacts of weak upslope will be maximized. Surface dew point depression will also remain lower with the the sheltered valleys locations. Look for development of IFR/LIFR fog as well. After sunrise Monday, look for the inversion to break in the west by the late morning. All locations are forecast to have VFR conditions by that time. Extended aviation discussion... High pressure will help provide for mainly VFR conditions Monday afternoon through Wednesday across the region. The exception will be isolated pockets of late night/early morning river and mountain valley fog. Thursday a bit more moisture will work its way north into western parts of the area on the west side of a departing high pressure. Isolated showers will be possible across the mountains, but for the most part, VFR conditions will still prevail. On Friday, there is a greater chance of showers, and possibly some storms, with the approach of our next cold front. Pockets of MVFR conditions will again occur briefly under the stronger showers or storms. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PC NEAR TERM...DS/PC SHORT TERM...RCS LONG TERM...RAB AVIATION...DS

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