Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 201314 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 914 AM EDT Wed Sep 20 2017 .SYNOPSIS... A weak short wave will move southeast across our region today, then high pressure follows for tonight through Saturday. A cold front will approach the Mid Atlantic region the middle of next week. Tropical Storm Jose will drift north off the east coast today. && .NEAR TERM /THROUGH TONIGHT/... As of 914 AM EDT Wednesday... Adjusted temperatures with latest surface obs, trends and shaped towards GLAMP for late morning into this afternoon. Morning fog and low clouds mixing out or lifting similar to recent morning. WSR-88d showed isolated showers in Greenbrier associated with weak shortwave. The best chance of convection this afternoon will be in the west with westerly winds hindering storm development in the east. Increased cloud cover for this morning with latest satellite images and blended late morning towards conshort. More changes later this morning... As of 325 AM EDT Wednesday... GOES 16 water vapor loops show a short wave over Indiana early this morning with a secondary vorticity maximum over western North Carolina. The Indiana wave will track southeast to the Tennessee/North Carolina border by this evening, and a nearly closed off 500MB low remains over western Virginia and North Carolina overnight. Very subtle if any surface reflection of these features, perhaps a lee-side trof by this evening. Overall low level winds remain northwest today then 850MB winds become east late tonight. Forecast location and amount of deepest moisture today varies depending on the model. Northwest winds suggest that best probability of precipitation will be over the mountains. Expecting enough heating today, with only scattered to broken mid level clouds in the morning that air mass will become unstable enough to support isolated thunderstorms during the afternoon. Maximum temperatures today and minimum temperatures tonight will be similar to past few days. && .SHORT TERM /THURSDAY THROUGH SATURDAY/... As of 330 AM EDT Wednesday... Very slow-evolving, amplified mid-level pattern remains offered by deterministic and ensemble solutions for the late week/early weekend period. Lower than normal mid-level geopotential heights should predominate the western third of CONUS, with downstream amplified ridge with accompanying milder than normal temperatures in place for many areas east of the Rockies. Only limited chances for showers and thunderstorms are forecast for this period, with temperatures running some 5-10 degrees milder than late-September climatology. Given the slow-evolving persistent pattern, bias corrected temperature schemes should perform quite well in this period. Will keep an eye on developments in the tropics pertaining to Jose and later Maria, though the most likely outcome at this point is to keep these two systems over the western Atlantic, well away from the region. Interests are advised to continue to monitor the latest forecast advisories on Jose and Maria from the National Hurricane Center. The best chance for showers in this period is on Thursday as energy associated with weakening mid-level shortwave trough now across the Ohio Valley gets shunted southward and westward into the Carolinas. Differential heating and enough surface convergence along the central Appalachians into the southern Blue Ridge may produce some isolated to widely scattered showers or garden-variety storms. Shown pops in the 15-30% range along and southwest of a Lewisburg-Roanoke- Danville line Thursday. Not expecting any significant storms as convective depth stands to be rather shallow given dry mid-level air in place and surface-based CAPES at/below 1000 J/kg. Any showers or storms should follow a diurnal trend and dissipate with sunset. Beyond Thursday, we look to be entrenched in a mostly sunny and dry weather pattern for the foreseeable future - at least through the end of the weekend. With little change in air mass, highs through much of this period are in the 70s to mid 80s with lows mid-50s to low 60s, generally mildest in the urban centers such as Roanoke, Danville and Lynchburg. && .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... As of 130 PM EDT Tuesday... Surface and upper ridge will be sandwiched between tropical systems off the east coast and strong upper trough over the central/western U.S. this period. Will see how Hurricane Maria evolves and tracks northward off the east coast, depending on how Jose moves/weakens and if the upper ridge pushes further off the mid- Atlantic coast. At present, models in decent agreement keeping us on the warm and dry side. Highs and lows will continue to range about 3 to 8 degrees above normal. && .AVIATION /13Z WEDNESDAY THROUGH SUNDAY/... As of 740 AM EDT Wednesday... MVFR to LIFR fog in the valleys this morning and MVFR fog in the foothills and piedmont of Virginia and North Carolina. High confidence all of the fog to dissipate by 14Z. A weak short wave will be reaching the central Appalachians in the morning which would result in more cloud cover and scattered showers over the mountains. Radar already showing a small cluster of showers just west of KLWB. Low confidence on the probability of any thunderstorms. Any chance would be after 16Z/noon. Brief dips to MVFR ceilings in the localized downpours will not be out of the question. Low confidence in narrowing down the most likely location of showers and thunderstorms this afternoon. Extended Aviation Discussion... Overall persistence forecast to prevail for the rest of the week, but with a lower probability of precipitation than today. Strengthening high pressure remaining in place between exiting Jose offshore and a weak cold front approaching from the west. This should maintain good flying weather outside of isolated diurnal showers possible Thursday afternoon as upper level energy slides across. Dry weather is expected Friday through Sunday. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AMS NEAR TERM...AMS/KK SHORT TERM...AL LONG TERM...WP AVIATION...AMS/JM

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