Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 292356 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 756 PM EDT Wed Mar 29 2017 .SYNOPSIS... High pressure will build into our region from the north tonight, then slide east and offshore on Thursday. The next storm system arrives from the west triggering showers and thunderstorms during Friday. Mainly dry weather is expected over the weekend in the wake of this system. && .NEAR TERM /THROUGH THURSDAY/... As of 645 PM EDT Wednesday... No major changes are in store for the early evening update. The one change reflects less cloud cover across the area currently, and through the next few hours, as compared to the previous forecast. We still anticipate a return of clouds, and some light upslope patchy light rain, along and near the crest of the Blue Ridge, but with an onset now a little later than previously advertised. Have also adjusted hourly temperatures, dew points, and winds based upon the latest observations and expected trends through the evening hours. As of 310 PM EDT Wednesday... High pressure has begun building into the region this afternoon from the north to start setting up a wedge. Easterly flow around the high has allowed clouds to develop for areas in the piedmont. The mountains will also begin to see some cloud cover in the evening to overnight hours ahead of a low pressure system moving in from the west. Temps tonight should remain relatively mild due to this cloud cover. Virga, eventually turning to rain falling into the dry lower layers should cause the cloud deck and temperatures to fall. High temps tomorrow should be much cooler than today, much closer to normal. Trended toward the higher end of guidance for the low temps tonight, and the lower end for highs Thursday. Expect precip to begin mainly along the Blue Ridge through North Carolina, and become more widespread over the course of the day Thursday as the cold front approaches. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/... As of 230 PM EDT Wednesday... Onset of more significant rainfall will start Thursday night as deep southeast flow transitions to a more south/southwest trajectory in advance of a warm front approaching from the southwest. This aided by initial upslope flow ahead of an axis of deeper moisture along a lead shortwave ejecting east from the parent midwest upper system. Models appear a bit fast although increasing support along with strong diffluence above a sharp 850 mb theta-e gradient would suggest a quick uptick in pops to likely/categorical by daybreak Friday. Guidance even showing some weak instability late Thursday night over the southwest near the approach of the triple point to the west so added a thunder mention there. Appears south/southeast winds again quite gusty across the highest elevations but below advisory levels given deep saturation and limited mixing below. Lows mostly in the 40s to lower 50s as could even rise some late as warmer air aloft arrives. Main period of more widespread heavier showers likely Friday morning into early afternoon as the upper low to the west swings a front aloft across the region. This should allow some deeper warm air to the south to spill north with a few hours of moderate to perhaps heavy rain decreasing during the afternoon as a mid level dry slot arrives. Likely to be some embedded thunder as well espcly closer to the warm front/triple point lifting across the south and west. This also supported by a strongly sheared environment while severe potential possibly limited via rainfall and some degree of wedging pending just how fast the cool pool lifts out Friday. Expect added convection Friday afternoon mainly east where more heating possible if can get some breaks behind the axis of deep moisture, and ahead of the actual upstream cold front as cooling aloft takes place. Otherwise upwards of an inch of rain or more possible espcly Blue Ridge with high pops tapering from the southwest by Friday evening. Highs Friday all dependent on when the heavier rainfall exits, as for now staying on the cooler side of Mos, per the initial wedge and lingering clouds/showers until late that should hold most in the 60s. Wave departs offshore Friday night into Saturday leaving decent northwest upslope flow in place as post frontal cool advection kicks in. This should bring an end to showers across the far east by Friday evening with pops mainly confined to the northwest ridges espcly Friday night into Saturday morning where high end chance to low likelys on tap. Elsewhere downslope drying under a gusty northwest breeze to bring clearing skies later Friday night and a cool but mainly sunny day Saturday under slowly diminishing winds. Lows Friday night mostly in the 40s under steady cooling aloft, then 50s/around 60 mountains Saturday to some downslope aided low 70s southeast. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... As of 200 PM EDT Wednesday... Shortwave ridging will take hold to start the period as surface high pressure builds in from the northwest making for a dry/pleasant end of the weekend. This will basically be between systems as the surface ridge ends up wedging south along the Mid-Atlantic coast by Sunday night. Similar to past events, expect south/southeast flow ahead of the next vigorous southern stream upper low heading out of the southern Plains to start generating low clouds later Sunday night, with spotty light rain or drizzle possible southern Blue Ridge late. Lift will then steadily increase along with stronger overrunning late Monday into early Tuesday as the main wave passes to the west and a warm front pushes north into southern sections Tuesday morning. This will bring another round of at least light/moderate rain espcly Monday afternoon into early Tuesday before the warm front passes north per latest wetter ECMWF. Convective threat again focused along the retreating warm front and perhaps within the warm sector Tuesday pending timing and subsequent heating ahead of the trailing cold front Tuesday afternoon. System exits Tuesday night into Wednesday with shortwave ridging returning, allowing for a period of drier weather for middle of next week. High temps to stay above normal, mainly 60s mountains to low 70 east, except cooler within the wedge Monday when some 50s could occur. Lows to start out on the cool side, mostly 40s, before rebounding under clouds/warm advection to mainly 50s into midweek. && .AVIATION /00Z THURSDAY THROUGH MONDAY/...
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As of 745 PM EDT Wednesday... VFR conditions prevail across the region with limited coverage of clouds in general through approximately 03Z/11PM to 05Z/1AM. Confidence is high that cloud cover will develop over the region overnight as southeast flow allows for upslope development along and near the crest of the Blue Ridge. Areas closest to the Blue Ridge can expect ceilings to drop into the MVFR range, with low end VFR common farther east across the Piedmont, and farther west into parts of West Virginia. Patchy light rain will also develop in the preferred upslope region with visibilities remaining VFR through the forecast period. Any sub-VFR ceilings will likely remain at those levels through the remainder of the latest TAF forecast period. Confidence in the general trend through the forecast period is moderate to high. Confidence specific boundaries between VFR and MVFR ceilings low to moderate. Extended Aviation Discussion... Thursday night into Friday, a storm system will begin moving toward the region. Highest rain chances look to be on Friday. Sub-VFR ceilings and vis are likely with these showers and potentially an isolated thunderstorm passes through. With frontal passage, MVFR and IFR conditions look to persist over the mountains and gust winds will be possible.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/PH NEAR TERM...DS/JR SHORT TERM...JH LONG TERM...JH AVIATION...DS/JR/PH

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