Area Forecast Discussion
Issued by NWS Blacksburg, VA

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714 FXUS61 KRNK 240549 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 149 AM EDT Sat Sep 24 2016 .SYNOPSIS... Cold front arrives from the north today, moving south into the Carolinas Sunday, before stalling. Another cold front will shift in from the west Tuesday. && .NEAR TERM /THROUGH TODAY/... As of 140 AM EDT Saturday... No significant changes needed at this time. Forecast appears on track with clear skies overnight. Fog development will be patchy and favors areas in southside Virginia and the northwest NC piedmont per higher dewpoints, as well as the river valleys in the mountains. As of 745 PM EDT Friday... Temperatures were running quite a bit warmer than forecast, so had to raise them a few degrees over the next few hours. Otherwise, forecast on track with no cloud cover and zero pops through much of the night. As of 310 PM EDT Friday... An upper level trough across the southeast coast will move offshore tonight. Heights will build behind this trough from an upper level ridge centered over the southern Mississippi Valley. Heights will begin to lower again as a back door cold front approaches the area. This front may bring in low clouds and light rain late in the afternoon to the southern Shenadoah Valley. Even though the atmosphere remains stable, weak convergence over the foothills and along the Blue Ridge may also pop a few shallow showers in the afternoon. For now, the best chance for any rain will be north of I-64. Since this is a slow moving front, Saturday afternoon temperatures will once again be warmer than normal with widespread 80s, near 90F toward the NC/VA border. && .SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/... As of 250 PM EDT Friday... A upper level ridge will be building over the eastern part of the country through Sunday, then it flattens Monday into Monday night. Surface high pressure over central Canada will build southward and wedge down the east side of the Appalachians. A back door cold front drops south across the area Saturday night into Sunday. Initial, shaped the pops for the light upslope with the HiResW-ARW-east and NAM for Saturday evening into Saturday night. Low temperatures Saturday night will range from the mid 50s in the mountains to the mid 60s in the Piedmont. Look for much cooler conditions behind the front Sunday with a good deal of low level moisture and isentropic lift over the wedge. The wedge looks to be solid and wet bulb temperatures are in the 60s so any precipitation into the wedge will be effective in holding temperatures down. Lowered high temperatures Sunday to the upper 60s in the north with wedge to near 80 degrees in far west. Sunday night will feature plenty of clouds and potential for some light upslope rain showers. Low temperatures Sunday night into Monday morning will generally be from the mid 50s in the northern mountains to the lower 60s in the southeast. By Monday evening, the axis of the upper ridge will move to our east and allow a large closed low over the Great Lakes region to push a cold front toward the region from the west. Southwest flow ahead of the front will continue to generate lift over the wedge, while the western and southern portions of the region on the fringes of the wedge may get into enough unstable air to support a slight chance of thunderstorms. Highs on Monday will range from the around 70 in the northeast to the upper 70s in the western mountains. Monday night will cloudy with chance of showers. Elected to increase pops to allow for the mention of likely in northwest Greenbrier county in Southeast West Virginia. Low temperatures Monday night will vary from the lower 50s in the northwest mountains to the mid 60s in the Piedmont. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 230 PM EDT Friday... A deep upper level low over the Great Lakes will slowly push a cold front into the region Tuesday. The front and a secondary trof axis should continue to move east Tuesday night into Wednesday and push further off the coast Wednesday night into Thursday. (The 12Z GFS is on the slow end of the guidance envelope, while the 00Z ECMWF shows a more progressive solution with the surface cold front passage.) Decided to used Superblend with ensemble solution approach for the timing with the front. High pressure will build east across the region Thursday and Friday, then slide into the Atlantic ocean on Saturday. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... As of 745 PM EDT Friday... Could see fog at all but BLF/ROA/LYH this morning. At Danville, there is fog forming southeast of this terminal as of 530z. With higher dewpoint air remaining, there is a good chance of low end MVFR/high end IFR vsby here around 08-12z. Across the mountains, confidence is not that high, but enough to keep tempo of LIFR at LWB, but bumped vsbys up at BCB to 3sm, as airmass stays dry. However, with light northwest wind fog along the New River could advect into BCB toward 11-12z. Otherwise will see VFR conditions this period. Cold front backdooring from the north looks to bring some mid deck into the LWB-ROA-LYH corridor by early afternoon reaching BCB/DAN late in the day. Models favoring along and west of BCB-BLF with scattered clouds. Lowering of ceilings to low end VFR expected at ROA/LYH and possibly BCB by end of the taf period. Extended aviation discussion... As the weekend progresses and the backdoor front stalls just to our south allowing easterly flow to become established across the region, low-level moisture increases and a wedge evolves. Expect cigs to lower into the MVFR category or worse Sunday morning and likely remain in place through Monday with areas of fog and drizzle or light rain developing with time as well, especially along the east facing slopes of the Blue Ridge. A strong, but slow moving, cold front will be approaching the area from the west on early Tuesday. Models have significant differences on the timing and location of this front, but rain chances during the first half of next week will be on the increase. Until the front pushes across, Tuesday, we should stay in a period of sub-VFR at times, especially northeast of a line from LWB-BCB-DAN. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...WP NEAR TERM...RAB/RCS/WP SHORT TERM...KK LONG TERM...KK AVIATION...RAB/RCS/WP is the U.S. government's official web portal to all federal, state and local government web resources and services.