Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 261742 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 142 PM EDT Mon Sep 26 2016 .SYNOPSIS... High pressure will remain wedged against the east side of the Appalachians today. Meanwhile a cold front will be moving east across the Ohio Valley. This front will pass through the area tonight bringing showers and thunderstorms. && .NEAR TERM /THROUGH TONIGHT/... As of 915 AM EDT Monday... Made some minor adjustments in temperatures utilizing surface obs and trends, then shaped towards Lamp guidance for late morning into this afternoon. Increased pops in the east for this morning to capture prefrontal convection highlighted on HRRR and HiResW- arw-East. Cold front will move east...approaching the appalachians this afternoon and move across our area tonight. There is a Marginal Risk for severe storms across West Virginia into Alleghany highlands in Virginia this afternoon and evening, the main threat from strong damaging wind gusts. More changes later this morning. As of 430 AM EDT Monday... High pressure will remain wedged against the east side of the Appalachians today...east-southeast wind flow resulting in upslope cloudiness drizzle and fog. West of the Appalachian divide, downslope wind flow will result in a lot less cloud cover with little or no precip until the arrival of a cold front later in the day. A surface cold front extends south from the Great Lakes into the western OH/TN valleys. This front is forecast to move east...approaching the appalachians this afternoon. An axis of instability just ahead of the front will fuel scattered to numerous showers and thunderstorms, some of which will be rather strong as they move into West Virginia during the peak heating hours of the afternoon. There is a Marginal Risk for severe storms across West Virginia this afternoon and evening, the main threat from strong damaging wind gusts. These storms are expected to weaken as they cross the mountains this evening, encountering the stable airmass, cool wedge, on the east side of the mountains. Never the less, still anticipate a period of moderate to heavy showers this evening and early tonight with potential for a half inch of rain as the front moves over and east of the Blue Ridge. Forward progress of the front is expected to slow per the upper level support lagging, models trending toward a slower solution with respect to the eastward push of the front with time. Temperatures today will be relatively mild in spite of the cloudiness with highs in the 70s. Any sun, and we could easily test 80. Slower frontal progress also means lingering warmth tonight, especially east of the Blue Ridge where we are looking at another night with minimums above 60. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 400 AM EDT Monday... The Cold front will continue to slowly cross the region from west to east early Tuesday in advance of a closing upper low rotating through the Great Lakes into midweek. Synoptic scale models continue to trend slower with the frontal passage, and differ widely with the ultimate stalling location of the boundary. For now, have slowed the progression of said boundary by a few hours out of respect to the ECMWF and GFS solutions. All in all, expect to see impacts in the form of broken to overcast skies and scattered showers mainly east of the Blue Ridge Mountains through the day Tuesday, with a rumble of thunder or two possible in the far east if enough daytime heating is allowed, which for now seems doubtful. Boundary likely to stall just southeast of the area Tuesday night. Models begin trending differently at this point, with smaller scale solutions allowing the boundary a bit more progression toward the coast and introducing cold air advection more rapidly, while the GFS/ECMWF have it sliding back NW as the low begins to slip down into the mid-Atlantic Wed/Thr. With this uncertainty, have re- introduced POP/QPF values a bit earlier in the east, but continue to keep temperatures trending cooler into midweek with cloudcover and cold air advection in play, especially to the west. Appears enough progged 850 mb cooling out west under a period of clearing and light winds to result in some of the coolest lows of the season with low/mid 50s east, and 40s west including perhaps a few 30s deepest valleys outside of any fog by early Wednesday. Any drying between the frontal passage and the closed low will be short lived as the flow quickly backs aloft Wednesday in response to the upper low dropping south and deeper moisture to the east shifting back inland. This will bring a combination of increasing shower chances Blue Ridge east by afternoon with weak surface low pressure to the east, and showers along the western slopes along the leading edge of the deeper moisture axis on the front of the upper low. Kept pops mostly low end chance most sections with less southern Blue Ridge for now where expecting a gap between the two. Otherwise becoming partly/mostly cloudy with highs mostly 60s mountains to low/mid 70s east. && .LONG TERM /THURSDAY THROUGH SUNDAY/... As of 400 AM EDT Monday... Trend toward a cloudier/wetter and much cooler scenario continues at least to start the period with models swinging a strong upper low from the Ohio Valley early Thursday morning southeast into/and around the region into early next weekend. This would allow for some degree of deeper moisture with the residual front along the coast to get swung back inland around this feature, espcly by weeks end per latest GFS. However, model spread remains rather large with earlier ECMWF farther to the southwest with this feature, while the 12z GFS much stronger now with the cold pool about directly overhead Thursday into Friday night before the upper low lifts out. Latest ensembles were closer to the earlier weaker 00z runs excluding the Euro with a much weaker upper system keeping most showers to the north and east. Since great uncertainty plan to just continue trend of including more chance pops Wednesday night into Friday night, at least for diurnally driven showers under the cold air aloft. Should finally see this slow moving system weaken and lift out during the weekend with drier air aloft spilling in. This will allow for a return to dry weather for later Saturday into Sunday although clouds may linger given possible redevelopment of another low level wedge under leftover weakness aloft at this point. Temps likely to be below normal under very cool air aloft with highs 60s to low 70s through Friday with potential 50s at elevation pending clouds. Some rebound likely during the weekend as highs slide back into the 70s overall. Lows also chilly, mostly 40s to low/mid 50s, with possibly even a few 30s again deeper valleys early Thursday if a period of more clearing develops early on. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... As of 142 PM EDT Monday... Poor flight conditions will persist this afternoon into tonight with cool moist airmass banked up against the east side of the Appalachians and cold front moving east across the region. Pockets of low clouds with ifr/lifr conditions persist right along the Blue Ridge per clouds intersecting the terrain. To the west, the cool wedge has been eroding ahead of an approaching cold front. Scattered MVFR showers and thunderstorms have developed this afternoon in the unstable air ahead of this cold front across the mountains. The cold front will push east into WV/KY by late afternoon and into the mountains this evening with a line of showers and a few thunderstorms. This convection is expected to diminishing as it reaches the more stable air created by the wedge. The front will work its way east tonight into Tuesday. The front will slow in its forward progression across the Piedmont Tuesday, so MVFR showers and a few thunderstorms may linger across that region as a result. Low to medium confidence in ceilings,visibilities and winds during the taf period. Extended aviation discussion... A wave moving along this front will stall the activity across the far eastern sections of the area on Wednesday, finally exiting Wednesday evening. Conditions will improve with mostly VFR to MVFR conditions within this time frame. During midweek, a rather unsettled pattern is expected to evolve as a deep upper low sags southward from the Great Lakes into the Central Appalachians. This will keep variable clouds, MVFR cigs, and periods of -SHRA across the region through much of the period. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PM NEAR TERM...KK/PM SHORT TERM...JH/JM LONG TERM...JH AVIATION...KK/PM

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