Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 260636 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 236 AM EDT Sun Mar 26 2017 .SYNOPSIS... High pressure is off the coast in the western Atlantic, stretching back across the southeastern states. A deep area of low pressure will drift east over the Midwest tonight with a trailing cold south into Louisiana. A warm front will reside from the Great Lakes region to Lake Erie into Sunday. && .NEAR TERM /THROUGH TODAY/... As of 955 PM EDT Saturday... Satellite fog product showed some breaks in the high clouds over the mountains this evening. Seeing some low clouds forming on the eastern slopes of the Blue Ridge as far north as Watauga and Wilkes county. Models showed these lower clouds expanding northeast after 06Z/2AM. HRRR and other Hi-Res guidance have been consistent in bringing higher probability of precipitation into the mountains around 12Z/8AM. Have trimmed back chance of showers before then. Also adjusted low temperatures in a few locations mainly based on the expected cloud cover. An upper level ridge off the southeast coast will continue to play blocker and divert a closed low over the Midwest toward the Ohio Valley through Sunday. Meanwhile, a dry surface high pressure system has moved off into the western Atlantic, however it remains stretched back over the southeastern US. The combination of these two stable high pressure systems will keep the area dry into tonight. As the closed low enters the Ohio Valley tomorrow morning, prefrontal showers will slowly move eastward through the day. Rain showers will cross over the mountains in the morning, then over the foothills in the afternoon. By late afternoon and into the evening, these showers will track across the piedmont. Lingering stable surface high will still cover the area east of the Blue Ridge in the morning and into parts of the afternoon. This will limit storms from becoming to strong in the afternoon and reduce rainfall amounts. Some wind gusts up to 35 mph are possible in isolated stronger storms but chances are very low. Southerly flow around these systems and a slower entry of showers into the area will help Sunday temperatures warm into the lower to mid 60s across the mountains. With the later arrive of rain east of the Blue Ridge, temperatures will be able to warm into the low to mid 70s. && .SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/... As of 330 PM EDT Saturday... Upcoming week will be active nationwide as series of Pacific Low pressure systems propagate east across the CONUS. Leading system will be weakening as it moves northeast around the periphery of an upper level ridge of High pressure over the western Atlantic early Monday. A second shortwave will be close on the heals of the first, passing across the area Monday night into Tuesday. The overall result will be a threat for showers and isolated thunderstorms across our region from Sunday night through Tuesday night...qpf averaging about a quarter to a half of an inch. In spite of the weather being somewhat unsettled, it will be mild with temperatures running about 15 degrees above normal. Can`t rule out a strong thunderstorm or two Monday, but overall dynamic support appears to be lacking for anything organized. Tuesday`s trough passage may come through early enough to preclude an organized severe threat for our CWA, except for maybe the Piedmont. Instability and moisture are significantly more abundant Tuesday compared to Monday, but favoring the Piedmont and Tidewater where there will be higher CAPE and and better dynamic support aloft. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 400 PM EDT Saturday... Behind the Tuesday system, we will see a brief respite from the parade of storm systems as an area of high pressure from Canada filters southward into the area stabilizing and cooling the air mass. This should lead to a relatively precipitation free and slightly cooler period. Cannot completely rule out some light showers due to weak ripples in the flow aloft. Temperatures and dewpoints will drop about 10 degrees from the Mon-Tue period. By Friday, the next, and fairly potent, upper low tracks toward the area. However, there is considerable discrepancy between the GFS and the ECMWF in the configuration and timing of this system into the eastern U.S. The GFS depicts more of an open wave reaching the CWA as early as Thursday night moving east of the area by Friday afternoon. Meanwhile, the ECMWF is much slower, deeper, and further south with a cutoff upper low lifting it slowly north-northeast into the Ohio Valley by late Friday. The difference between the two models can be accounted for in noting the strength and blocking of an upstream ridge across the Atlantic. This upstream ridge is much stronger per ECMWF, which also depicts a notable wedge down the east side of the Appalachians as the closed low lifts north into the Ohio Valley. The ECMWF would result in a much wetter and stormier pattern for the CWA, although it would not arrive until Friday as opposed to Thu night per GFS. For now, have generally broad brushed the area with high chance to likely pops beginning Thu night and continuing into Friday. In addition to the differences noted above, there are also massive differences between the two models regarding instability and the potential for severe, with the ECMWF much more noteworthy in this category. For now, have included a chance for thunder without any further details. It will likely take several runs for the models to resolve their differences on this system. Another system is slated to follow by the end of the weekend or the beginning of the next week, so the active pattern is expected to continue into the next week. Temperatures will be closer to normal Wed-Thu, then begin to trend back to above normal levels Fri-Sat. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... As of 235 AM EDT Sunday... A slow moving stacked low pressure system will move from the Mississippi valley into the Great Lakes region and push a frontal system into the area from the west. This will allow us to start Sunday with VFR at TAF sites, followed by precipitation spreading westward across the area and a trend for lowering cigs to MVFR by the afternoon along and west of the Blue Ridge. The downward trend will continue as we head into Sunday evening with MVFR spreading east of the Ridge and IFR setting in to the west, but any significant obvis looks to hold off until after this TAF period. Instability is largely absent but modestly steep mid/upper lapse rates may be able to support some rumbles of thunder. However, believe the expected chances and coverage of thunder is quite low so will not include any mention in the TAFs. The low level wind field will be amplifying west of the Blue Ridge as the low approaches and this will create some gusty conditions but wind speeds do not appear as if they will pose any significant issues for aircraft. Extended Aviation Discussion... An active weather period with a series of vigorous upper-level low pressure areas tracking from west to east across the U.S. during the week. Monday the area will be between systems, but a moist/unstable air mass will remain in place and widely scattered showers and isolated thunderstorms are possible. Areas of sub-VFR cigs/vsbys are also possible, especially during the morning hours, in low clouds and fog. The next upper-level low will arrive Tuesday with another chance for showers and thunderstorms along with periods of sub-VFR conditions. Wednesday-Thursday may bring a period of improved aviation conditions as a weak cold front temporarily pushes the deeper moisture south of the area. However, by Friday the next in the series of upper-level systems arrives with another chance for showers, thunderstorms, and sub-VFR conditions. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RCS NEAR TERM...AMS SHORT TERM...PM LONG TERM...RAB AVIATION...MBS/AL

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