Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 231850 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 250 PM EDT Fri Sep 23 2016 .SYNOPSIS... Low pressure along the coast of the Carolinas will weaken and head east tonight. A back door cold front enters the area by Saturday night. As it moves south of us Sunday the flow turns east which brings in more clouds and a threat of showers into early next week. && .NEAR TERM /THROUGH SATURDAY/... As of 100 PM EDT Friday... An upper level ridge over the southern Mississippi Valley will stretch east over the region this afternoon. This ridge will help push an upper level trough currently over the southeast coast, offshore. With heights building along with abundant sunshine, temperatures will warm into the 80s this afternoon. Previous morning discussion... Upper trough situated across the mid-Atlantic and Southeast will continue to weaken and get kicked eastward ahead of a digging northern stream shortwave over the northeast through late tonight. Model do cut off a piece of the upper energy and drift it southwest to southern Georgia. For our area the upper heights will begin to build as strong ridge pushes into the Mid Mississippi Valley. The few showers over southside Virginia into northwest NC will fade and/or shift southeast of the forecast area by mid morning. Should see increasing sunshine. There will be a difference in dewpoints from the mountains to the piedmont, ranging from the mid 50s west to mid 60s southeast. With drier air and sunshine temperatures are expected to warm into the 80s, except some upper 70s higher elevations. Tonight, the high pressure at the surface will keep light winds in place with mainly clear skies. Backdoor front expected to slide into northern Virginia by 12z Saturday and may push a few clouds toward the Shenandoah Valley but overall generally clear. Patchy fog in the river valleys possible in the west. Lows will vary from the mid 50s deeper valleys in the west to lower to mid 60s elsewhere. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
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As of 250 PM EDT Friday... A upper level ridge will be building over the eastern part of the country through Sunday, then it flattens Monday into Monday night. Surface high pressure over central Canada will build southward and wedge down the east side of the Appalachians. A back door cold front drops south across the area Saturday night into Sunday. Initial, shaped the pops for the light upslope with the HiResW-ARW-east and NAM for Saturday evening into Saturday night. Low temperatures Saturday night will range from the mid 50s in the mountains to the mid 60s in the Piedmont. Look for much cooler conditions behind the front Sunday with a good deal of low level moisture and isentropic lift over the wedge. The wedge looks to be solid and wet bulb temperatures are in the 60s so any precipitation into the wedge will be effective in holding temperatures down. Lowered high temperatures Sunday to the upper 60s in the north with wedge to near 80 degrees in far west. Sunday night will feature plenty of clouds and potential for some light upslope rain showers. Low temperatures Sunday night into Monday morning will generally be from the mid 50s in the northern mountains to the lower 60s in the southeast. By Monday evening, the axis of the upper ridge will move to our east and allow a large closed low over the Great Lakes region to push a cold front toward the region from the west. Southwest flow ahead of the front will continue to generate lift over the wedge, while the western and southern portions of the region on the fringes of the wedge may get into enough unstable air to support a slight chance of thunderstorms. Highs on Monday will range from the around 70 in the northeast to the upper 70s in the western mountains. Monday night will cloudy with chance of showers. Elected to increase pops to allow for the mention of likely in northwest Greenbrier county in Southeast West Virginia. Low temperatures Monday night will vary from the lower 50s in the northwest mountains to the mid 60s in the Piedmont.
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&& .LONG TERM /TUESDAY THROUGH THURSDAY/...
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As of 230 PM EDT Friday... A deep upper level low over the Great Lakes will slowly push a cold front into the region Tuesday. The front and a secondary trof axis should continue to move east Tuesday night into Wednesday and push further off the coast Wednesday night into Thursday. (The 12Z GFS is on the slow end of the guidance envelope, while the 00Z ECMWF shows a more progressive solution with the surface cold front passage.) Decided to used Superblend with ensemble solution approach for the timing with the front. High pressure will build east across the region Thursday and Friday, then slide into the Atlantic ocean on Saturday.
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&& .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/... As of 100 PM EDT Friday... High pressure enters the area this afternoon and tonight with VFR expected along with light winds. A potential for fog in the valleys exists again late tonight at BCB/LWB. Question is how low to go. Will follow the trend of what happened this morning so going LIFR at LWB and IFR at BCB by 10z/24. Extended aviation discussion... VFR conditions will prevail through Saturday with high pressure in place. A back door front passes across late in the weekend into early next week which may bring sub VFR ceilings as an easterly flow sets up. These MVFR or lower ceilings may stay in place through Monday. Rainfall chances will stay low however, though some upslope component from the southeast could bring showers/rain to along the Blue Ridge south of Roanoke/Blacksburg Monday. A strong, but slow moving, cold front will be approaching the area from the west on Tuesday. Models have significant differences on the timing and location of this front. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...WP NEAR TERM...RCS/WP SHORT TERM...KK LONG TERM...KK AVIATION...AMS/RCS

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