Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 211843 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 243 PM EDT Mon Aug 21 2017 .SYNOPSIS...
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High pressure will gradually move off the Mid Atlantic coast tonight, allowing winds to turn southerly and bring a return of deeper moisture to the region along with a chance for showers and thunderstorms mainly along and west of the Blue Ridge. A cold front will pass over the area Wednesday, bringing a better chance for showers and storms to the Appalachians and central Mid Atlantic region.
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&& .NEAR TERM /THROUGH TUESDAY/...
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As of 200 PM EDT Monday... Surface high pressure will continue to move off the Virginia and Carolina coast tonight. Return southwesterly flow will maintain an influx of heat and humidity into the region. Under a weakly capped environment this afternoon, upslope flow has generated isolated showers and thunderstorms across the eastern slopes of the North Carolina High Country and southwest Virginia Blue Ridge. Some instability showers have also popped across the piedmont. Some lack in coverage is due to the eclipse as heating is temporarily halted. Some storms may continue into this evening as they track east in zonal flow, but will fade with loss of heating. Skies should be mostly clear through midnight then high clouds will advance over the area through the early morning hours. These high clouds should not be thick enough to deter patchy fog from forming in mountains and river valleys. Overnight conditions will remain muggy with lows in the 60s. Surface high pressure will lose its influence on our weather by Tuesday afternoon. A lee trough and southerly upslope flow may help generate a few storms across the mountains through the afternoon, but coverage may be limited with increase mixing ahead of an approaching front. Any diurnal showers will fade with loss of heating. There is a small chance that prefrontal showers may make it to the western slopes of SE WV and SW VA by evening, however the bulk of the showers will come with the front Wednesday. With limited coverage of showers, abundant sunshine and southerly flow, afternoon temperatures Tuesday will warm into the mid to upper 80s across the mountains to the lower 90s across the foothills and piedmont.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
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As of 230 PM EDT Monday... Short wave crosses through the base of a broad, somewhat flat upper trough of Monday night. This will result in a chance of showers Tuesday night. Better upper diffluence and coverage of precipitation will be approaching southeast West Virginia by 8AM/12Z Wednesday morning. 00Z ECMWF was bringing a pre-frontal trough and front through southern West Virginia, Virginia and northern North Carolina on Wednesday, with reasonable agreement from the 12Z NAM and GFS. The earlier in the day the front crosses through, the less instability will be available for showers and thunderstorms until the front gets farther east. Cloud cover from ongoing precipitation upstream Wednesday morning will also limit instability in the mountains. Higher probability of showers and thunderstorms Tuesday night and Wednesday will remain over the mountains due to the west wind that will be in place ahead of the front. By Wednesday evening the focus will shift to the piedmont of Virginia and North Carolina. The front and deeper moisture may be slow to exit southern Virginia and northern North Carolina. Clearing in those locations may not occur until late Thursday.
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&& .LONG TERM /FRIDAY THROUGH SUNDAY/...
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As of 130 PM EDT Monday... Deeper upper trof develops in the eastern United States with the Canadian, ECMWF, and GFS showing another strong short wave/potential upper low re-enforcing the trof over the Great Lakes on Monday. For the Mid Atlantic region the primary long wave trof axis will cross through the area on Friday. Then not much recover in 500 MB heights through Monday. By Friday morning 850MB temperatures are down to around +12. At the surface a large high passes through the Great Lakes on Friday, then wedges down the east side of the Appalachians on Saturday through Monday. Surface dew points and precipitable water values also drop by Friday, down under an inch for precipitable water and into the 50s for dew points. Saturday, Sunday and Monday some trapped or return low level moisture in the northwest North Carolina mountains, spreading north, west of the Appalachians each consecutive day. Sunday also has the potential for scattered to broken mid and high clouds along with the passage of a warm front from the west. Will keep the forecast dry Friday and Friday night with below normal temperatures through Sunday.
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&& .AVIATION /19Z MONDAY THROUGH SATURDAY/... As of 120 PM EDT Monday... Surface high pressure will slide off the VA/NC/SC this afternoon, then further out to sea on Tuesday. Return southwesterly flow will continue to bring in more heat and humidity. Upslope flow and afternoon instabilities may produce scattered showers and thunderstorms along the Blue Ridge this afternoon. The highest chance for afternoon convection will be along the eastern slopes of the northwest North Carolina Blue Ridge. Convection activity and coverage may be less this afternoon as the solar eclipse will reduce heating for a few hours. Any convection lingering past the eclipse will fade with loss of heating this evening. Clearing this evening will likely lead to fog forming in mountain and river valleys. Outside of any fog formation, high confidence in VFR conditions prevailing through the period. Extended Aviation Discussion... Moisture will continue to increase on Tuesday as high pressure moves farther offshore ahead of another cold front that will arrive from the northwest Wednesday. This will again lead to more afternoon clouds and isolated convection across the mountains Tuesday afternoon but overall VFR at this point. Better potential for sub- VFR will come Wednesday when more widespread showers and storms arrive with the next cold front. Flying conditions should slowly improve behind the passing cold front on Thursday although sub-VFR cigs may linger across southern/western sections a while longer. && .EQUIPMENT... As of 930 AM EDT Monday... KFCX doppler radar is expected to be back in operations as early as Wednesday evening (Aug 23rd). Technicians have replaced the bull gear and are reassembling the radar today and tomorrow with calibration worked on Wednesday. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RCS NEAR TERM...RCS SHORT TERM...AMS LONG TERM...AMS AVIATION...RCS EQUIPMENT...RCS

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