Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 152311 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 711 PM EDT Fri Sep 15 2017 .SYNOPSIS... High pressure will build over the Mid Atlantic region tonight and cover much of the eastern United States through Sunday. Hurricane, or remnants of, Jose will track north well off the east coast Monday and Tuesday, then track close to the New England shore Wednesday before turning to the northeast Thursday. && .NEAR TERM /THROUGH SATURDAY/... As of 644 PM EDT Friday...Rather steep surface-700 mb lapse rates combined with trapped PBL moisture underneath surface high helping to lead to a pretty extensive stratocumulus field late this afternoon across the western Appalachians to the Blue Ridge. Coverage of cumulus a little less out in the Piedmont of VA/NC. Already noting some decrease in such cloudiness back into eastern KY/southern WV and as PBL stabilizes a continued decrease is expected. Still, am not entirely convinced skies will be fully clear based on extent of lingering moisture depicted in RAP- based BUFKIT fields, particularly to the north and west. Clearing or breaks in cloudiness should lead to shallow radiation inversion and development of at least patchy fog as the nighttime hours progress. Given very light flow, wouldn`t rule out possibility of pockets of locally dense fog overnight, though extent may be limited with the best shot in areas where skies can stay clear the longest and also near climo favored river valleys. Otherwise looking at relatively quiescent conditions tonight with lows ranging from the low/mid 50s to the lower 60s. Previous near-term discussion issued at 210 PM follows... Surface high pressure will cover the Mid Atlantic region and much of the eastern United States tonight and Saturday. Low level moisture remains trapped under a slowly building upper ridge but 12Z/8AM sounding and models showed dry mid and upper levels of the atmosphere. Expecting a persistent pattern of a strong, but shallow, surface based inversion forming overnight, leading to fog and stratus in the morning, which then lifts into a scattered to broken stratocumulus layer. More questionable is any probability of precipitation. This will be during daytime heating since there is no upslope nor any other forcing on a meso or synoptic scale. Similar to the weather pattern this morning, once fog and low clouds mix out, temperatures on Saturday will climb well into the 70s. Lows 80s are likely in the foothills and piedmont were 850MB temperatures reach about +16C. Will stay cooler than guidance for minimum temperatures tonight, based on the MAV/MET performance this morning. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... As of 230 PM EDT Friday... There are two main weather features for the period. News headlines will focus on newly upgraded Hurricane Jose in the western Atlantic tracking off/along the east coast. The second features is a warm upper level ridge centered in the western Gulf stretching northward into the Ohio Valley. It is the upper level ridge that has the better chance to bring showers into the region than Jose. Impulses on the outer rings of the ridge will bring a chance for showers across the mountains each afternoon. Downsloping northwesterly flow should limit showers from moving east of the Blue Ridge Tuesday. However, an area of convergence may develop over the area Monday afternoon as Jose`s position is parallel to VA/NC. Both systems will provide moisture and convergence will give the necessary lift for showers. If Jose tracks closer to the VA/NC coast than currently forecast, this may place the region in a subsidence zone further limiting the chance for showers. For now, confidence is low to keep PoPs in the 20%-30% range for Monday afternoon. In any case, afternoon showers will likely fade each evening with loss of heating. Afternoon temperatures will be near seasonal with mid to upper 70s across the mountains and low 80s east. Overnight lows will run 3F to 6F warmer than normal with lows in the 60s. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 250 PM EDT Friday... Hurricane Jose will track north, remaining off the New England shore Tuesday then turns to the northeast and away from the US mainland Wednesday. Windy to possibly tropical-storm-force winds may impact northeast coastal states Tuesday night into Wednesday, but landfall is not expected. Based on the 12Z GFS, our area will have a chance for showers Tuesday and Wednesday afternoon as an upper level ridge continues to send weak impulses over the region. The GFS then has high pressure moving in behind Jose and wedging south into the Carolina by the weekend. The ECM keeps the area dry Tuesday and Wednesday as Jose continues to keep subsidence over the region. The ECM, moreso the 00Z than the 12Z, then has Jose doing a loop off the northeast coast Thursday and inland into New York next weekend. With a high degree of uncertainty, we will keep PoPs low through the period. Likewise on temperatures forecast, keeping near seasonal levels. && .AVIATION /23Z FRIDAY THROUGH WEDNESDAY/...
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As of 711 PM EDT Friday... SCT-OVC VFR stratocumulus ceilings should persist through 02z with thinning anticipated as boundary layer stabilizes. Question for tonight from an aviation perspective is on degree of cloud clearing and the extent of overnight IFR to LIFR fog. Recent guidance indicates that fully clear skies don`t look likely overnight but should clear sufficiently enough. Given winds under 10 knots through a deep depth of atmosphere, these are conditions that should promote patchy fog development. Indicated a general IFR mist (though VFR at Roanoke) developing no sooner than 04z, with temporary LIFR fog at Blacksburg, Lewisburg and Danville after 07z. These latter sites have the best chance of longest clearing and/or are located near favored river valleys. Confidence on extent of fog and visibilities only medium. Any overnight fog should burn off by mid-morning to reveal FEW-SCT VFR stratocu Saturday. Surface winds through the 00z TAF forecast period are light to calm. Extended Aviation Discussion... Areas of LIFR to MVFR fog in the favored mountain and river valleys are likely each night through Wednesday. The chance of precipitation remains low for Sunday. Monday there will be enough low level convergence for diurnal isolated to scattered showers and thunderstorms. Tuesday and Wednesday may feature some isolated MVFR showers in the mountains.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RCS NEAR TERM...AL/AMS SHORT TERM...RCS LONG TERM...RCS AVIATION...AL/AMS

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