Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 150528 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1228 AM EST Wed Nov 15 2017 .SYNOPSIS... With the exception of a weak cold front bringing a chance of showers Wednesday night, fair weather will prevail across the Appalachians and central mid Atlantic region through the end of the workweek. A strong cold front will then bring more showers and windy conditions to the region this weekend. && .NEAR TERM /THROUGH TODAY/... As of 140 PM EST Tuesday... Uneventful weather with a lot of cloud cover through Wednesday. Wedge of high pressure is keeping low level moisture locked in across the Appalachians and central mid Atlantic. Expect east of the Blue Ridge may be able to slowly mix enough of the boundary layer to help break up the clouds, but locations west of the Ridge will likely stay in clouds until later Wednesday morning. However clearing in the east will lead to fog formation toward daybreak. By late Wednesday morning low clouds in the west dissipate just in time for higher clouds associated with a cold front approaching from the west to start moving in, while some low level moisture may spread some lower clouds into eastern sections. With lots of clouds expected, temperatures overnight look to be fairly uniform in the low/mid 30s, though if clearing develops earlier of is more aggressive than thought some locations may get colder. Highs tomorrow will continue on the cool side with low/mid 50s expected. && .SHORT TERM /TONIGHT THROUGH FRIDAY/... As of 200 PM EST Tuesday Next upper trough will pass well to the north Wednesday night with a preceding cold front pressing east into the mountains after midnight, and into eastern sections by early Thursday. Guidance continues to slow up the associated shower band with the boundary with much of the focus remaining over the west given downslope drying westerly flow east of the Blue Ridge. Also best dynamics look to swing by to the north given lack of much digging aloft. Therefore slowed up the onset of most showers until later Wednesday evening, while trending with mainly upslope driven post frontal showers overnight. However no higher than chance pops at this point given only weak upper support. Spoke of energy rotating around the upper low lingering to the north may keep some degree of upslope clouds/showers going far northwest into Thursday morning. Otherwise expecting good drying under shortwave ridging including surface high pressure sliding in from the west. This should result in increasing sunshine Thursday with temps jumping into the 60s east ahead of lagging cool advection with values leveling off in the 40s to mid 50s west behind the front. High should be overhead Friday allowing for another mainly sunny and cool day including uniform highs mostly in the low/mid 50s. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... As of 130 PM EST Tuesday... Rather flat upper flow across the region to end the week will quickly transition to strong upper troffiness over the weekend into early next week as a strong cold front pivots across by early Sunday. However timing of the front remains a bit uncertain given differences between the much slower ECMWF/ensembles and the fast GFS that swings the boundary across on Saturday. Latest guidance means suggest a trend more toward the slower solutions as the fast GFS looks too quick espcly given lagging upper support to the northwest. Otherwise warm front lifts north Friday night giving way to increasing warm advection overnight including gusty southwest winds on the ridges per 30-40+ knot 850 mb jet. Moisture lacking with this feature with best lift still to the west ahead of the cold front so keeping things dry Friday night. Surface cold front likely to cross the region later Saturday with perhaps the surface wind shift along the leading edge of the associated shower band. Latest GFS supports a swath of showers crossing the region later in the day into the evening with perhaps an embedded/narrow band of shallow convection, but without thunder per lack of forecast instability at this point. Precip may switch to western snow showers Sat night pending how fast the cold advection behind the front catches up but iffy elsewhere outside of the higher western elevations given slower timing. Main concern will be with post frontal northwest winds as strong cold advection follows the front on 40-45 kt 850 mb cross barrier flow. However model pressure rises show an initial surge in winds as the front passes, then a more prolonged round of gusty winds Saturday night into Sunday as more strung out pressure rises coincide with the coldest air aloft espcly from the late night hours of Saturday into Sunday night. Latest progged inversion levels remain rather high so likely looking at mainly mountain wind advisory criteria at times unless models trend even weaker. Therefore will continue mention in the HWO while expanding potential for stronger winds into Sunday. Upslope snow showers likely to linger into Sunday evening before low level moisture fades with high pressure building in from the southwest making for quiet weather into early next week. Will turn abruptly colder behind the front with a swing from highs in the 50s/60s Saturday to 30s/40s west and only around 50 east under gusty winds Sunday. This before readings slowly rebound Monday into Tuesday to more seasonal levels as the upper trough lifts out. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
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As of 1220 AM EST Wednesday... Wedge of high pressure is keeping low level moisture locked in across the Appalachians and central Mid Atlantic. Clouds along and either side of the Blue Ridge will keep BCB/ROA in MVFR cigs through the morning, and could expand into BLF/LWB and LYH. Fog at LYH will stay IFR or better. By mid to late morning expect conditions to improve to VFR through the rest of the period. Extended Discussion... A period of sub-VFR conditions, brief showers and a west- northwest wind shift likely for the mountains Wednesday night. Possible post-frontal sub-VFR ceilings into Thursday in the western Appalachians, otherwise VFR conditions. VFR then anticipated through Thursday evening. A cold front is expected to cross through the Mid Atlantic region Friday and Saturday with precipitation and strong winds both ahead of and behind the front. Gusty winds may continue into Sunday but there is large spread in the guidance at that time frame.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...MBS NEAR TERM...MBS SHORT TERM...JH LONG TERM...JH AVIATION...AMS/WP

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