Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 181418 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 918 AM EST Wed Jan 18 2017 .SYNOPSIS... A cold front will move southeast to the coast by midday today. Weak high pressure builds over tonight, then another storm system moves over the southern Appalachians by Friday. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 918 AM EST Wednesday... Modified temperatures with latest sfc obs and trended towards GLAMP to capture warmer temperatures in the Piedmont with downslope wind. Made a few minor adjustments in pops for this morning. More changes later this morning... AS OF 630 AM EST Wednesday... Just a quick update to take pops out in the southeast, lower cloud cover a little quicker lee of the Blue Ridge and bump temps a few degrees warmer the next couple hours. Previous forecast discussion... Frontal boundary bisecting the forecast area this morning will slide southeast to the Outer Banks of NC west-southwest to the Gulf Coast states by early afternoon. Should see shower activity diminish this morning and temperatures in the west will star to drop off. A decent shortwave moves across the Central Appalachians into the mid- Atlantic during the morning to midday. A brief period of strong subsidence behind this will bring strong wind gusts to the higher elevations from around dawn to early afternoon. At the moment should stay under advisory level winds of 45 mph for gusts, though some of the elevations above 4000 feet in the NC mountains and Grayson Highlands should see some gusts to 45 to 55 mph for a few hours. Will only mention in the HWO and possibly a Special Weather Statement since coverage will not be great. This shortwave and northwest flow will also increase the moisture across the upslope side of the mountains in WV so keeping some pops in through the morning. 8h temps sink to zero or below briefly across the Alleghanys so some snow flakes possible in the Greenbrier mountains. Going with a somewhat non-diurnal temperature forecast mainly in the west where early morning temperatures still sitting in the upper 40s to mid 50s. Temperatures should drop to the upper 30s to lower 40s by the afternoon over WV with mid 40s to near 50 elsewhere west of the Blue Ridge. The foothills/piedmont will be in the mid 50s to lower 60s. Sunshine will finally make a return to most of the area except the mountains of WV. Tonight skies will be mostly clear with some increase late in the west of the high variety. Low temperatures as high pressure builds overhead should be in the 30s, but still a bit above normal for most areas for mid January.
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&& .SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/... As of 145 AM EST Wednesday... This portion of the forecast will be characterized by a series of upper level troughs that will progress northeast from the Four Corners region northeast into the Central and High Plains states. This scenario will keep our region within a mild, southwest flow regime with impulses ejecting across our region from off the eastern edges of the main upper troughs, all while tapping Gulf of Mexico moisture. The exception to this rule will be on Thursday when a brief upper level ridge swings trough the region bringing drier weather and more sun than clouds. Otherwise, Thursday night into Friday look for a band of widespread light to moderate rain to overspread the region. After a brief break Friday night into early Saturday, another round of light to moderate rain is expected move into and across the area late Saturday into Saturday night. For the most part, we will be forecasting stratiform rain with these pseudo-warm front features as they impact our region. The exception will be the western quarter of the region Friday afternoon where rain showers are forecast. Guidance is suggesting some weak surface based instability. Temperatures will be on the mild side during this part of the forecast, averaging around fifteen degrees above normal. && .LONG TERM /SUNDAY THROUGH TUESDAY/... As of 330 PM EST Tuesday.... The main concern for the extended period is the potential for significant precipitation, and to a lesser extent wind, in the Sunday/Monday time frame. Guidance has been consistent with developing a full latitude trof with a deep closed low over the deep south by Sunday night. Persistent southerly flow will allow for efficient moisture transport into the region and by Monday morning, precipitable water values will be approaching 1.2 inches which is near record territory for January. At the surface, occluded low pressure will be moving up the Mississippi valley with a frontal boundary pushing in from the west. With a very moist atmosphere, strong low level flow parallel to thew baroclinic zone, and orographic effects from the Blue Ridge, guidance begins to generate substantial rainfall on Sunday with a continuation through Monday as the front moves through. These parameters are consistent with heavy precipitation events, though we are still out in the day 6/7 time frame and much of this, especially in regards to timing and placement of heavy precipitation, is subject to change with later model runs so the situation will be monitored closely. Some embedded convection is also possible especially as the front moves through Sunday night/Monday morning so this is another aspect to watch in the days ahead. Lingering wrap around precipitation will continue as the large system unwinds and pulls off to the north early next week. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/... As of 630 AM EST Wednesday... MVFR ceiling should stay confined across BLF most of the period with the rest of the forecast area seeing an improvement to VFR between 14-18z. Winds will be gusty at least in the mountains, including Roanoke thru mid afternoon, then winds will trail off overnight with high pressure building in. Some gusts could exceed 30 mph. As high builds in tonight the lower cigs at BLF should erode as well becoming scattered by 02z. Extended Aviation Discussion... VFR conditions will prevail into Thursday. However, this is expected to be short-lived as moisture returns from the southwest. Expect periods of rain Thursday night-Friday night, then again Sunday into Monday. During this time expect sub-VFR cigs and at times vsbys. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...KK/WP NEAR TERM...KK/WP SHORT TERM...DS LONG TERM...MBS AVIATION...AMS/WP is the U.S. government's official web portal to all federal, state and local government web resources and services.