Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 221933 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 333 PM EDT Sat Jul 22 2017 .SYNOPSIS...
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A cold front will cross overhead during tonight into Sunday, which should spark showers and thunderstorms. This front should pass south of our region by Monday. High pressure will arrive to bring slightly cooler conditions by the middle of the week.
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&& .NEAR TERM /THROUGH SUNDAY/...
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As of 330 PM EDT Saturday... Scattered showers and thunderstorms have developed along the southern Blue Ridge, while the vast majority of the convection along the cold front to our north has remained well north of the CWA. SPC has a marginal risk of severe weather south of I-64 and a slight risk to the north. The latest high resolution models only clip areas north of I-64 later this evening. The heat and humidity has been impressive so far in the Piedmont with heat indices crossing into the 100-105 degree range at this time. Highs were bumped upward, especially in the Roanoke Valley as ROA is going for it in terms of a 100-degree high. Shower and thunderstorm coverage should remain scattered through the night as the cold front pushes southward over the CWA. High resolution models do hint at another round of convection arriving west of I-77 by early Sunday morning. Therefore, chance POPs were kept throughout most of the CWA tonight. Cloud cover from upstream convection could limit high temperatures from climbing as high by Sunday afternoon compared to Saturday afternoon. Still, it will be quite hot and humid, and the cold front may reach the VA/NC border by the afternoon. This situation should allow enough instability and lift for more scattered showers and thunderstorms to develop in this area toward the evening.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
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As of 230 PM EDT Saturday... For Sunday evening, weather forecast models are hinting at a line of thunderstorms entering our far western Virginia/northern North Carolina counties during late evening as an upper level disturbance passes overhead. Believe any storms would diminish in intensity quickly as they cross the ridges and move into downslope flow. Have introduced a period of higher rain chances across the west for the possibility of this system, however admit that confidence of the occurrence/timing/location of any organized line of storms moving in from the west is marginal. The coming overnight forecast shift will have the benefit of an updated set of models to have a look at and will make adjustments to these rain chances accordingly. Outside of these storms, convection is expected to diminish after sunset with the loss of daytime heating. Widely scattered showers and thunderstorms can be expected for Monday despite a cold front approaching from the northwest. Slightly drier air and stronger northwest wind flow will help to inhibit convective development, though those storms which do develop may pulse up to strong/severe intensity for brief periods of time, capable of producing localized damaging winds. The cold front will enter the southeast West Virginia counties during late Monday evening, and gradually loose momentum as it continue south across our area.
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/...
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As of 1230 PM EDT Saturday... Looking to Tuesday, long-range weather models are indicating that the cold front may not pass completely across our forecast region, possibly stalling near the Virginia-North Carolina border as high pressure shifts from the Great Lakes toward New England. Will hold close to the previous forecast of a higher chance of spotty afternoon showers/storms south of Highway 460...closer to the front. Passage of high pressure off the coast on Wednesday will bring cooler easterly windflow to the mid-Atlantic, resulting in likely the coolest afternoon temperatures of the week. Upslope wind flow will make for the best chances of shower/thunderstorm activity across the mountains. Winds will shift more southerly by Thursday, resulting in a return of warmer temperatures and higher humidity, and greater coverage of afternoon showers/storms, more so across the mountains. A cold front will slowly make its way across the mid Atlantic on Friday and Saturday, again resulting in scattered showers and thunderstorms both days, a few of which may become severe for brief periods of time.
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&& .AVIATION /19Z SATURDAY THROUGH THURSDAY/... As of 210 PM EDT Saturday... Scattered showers and thunderstorms will continue to develop over the remainder of the afternoon. The most organized convection should stay to the north, but the chances are good enough to keep VCTS for all TAF sites except DAN. Confidence is not high enough yet to mention thunder more strongly, but amendments will be made if needed through the afternoon. Otherwise, VFR conditions should persist outside of the showers and thunderstorms. There is a threat for severe weather, so turbulence will be an issue this afternoon. Another cluster of showers and thunderstorms could arrive overnight toward early Sunday morning near BLF and LWB, but confidence is too low to mention in the TAFs at this point. High clouds from convective debris upstream and a breeze through the night in the mountains will not permit fog to form. Scattered low clouds were kept for BLF and LWB due to the potential for MVFR ceilings. Ceilings and visibilities should be VFR during the day with winds starting to gust from the west just past 18Z on Sunday afternoon. Aviation Extended Discussion... Confidence is growing for the potential of a rather active period for Sunday afternoon and Sunday night. A cold front will be passing overhead, which should spark clusters of showers and thunderstorms. The models shift the front toward North Carolina by Monday with the potential for convection developing in the afternoon along the VA/NC border. However, most locations should remain VFR outside of the convection. Another cold front could push some of the moisture eastward by Tuesday, but high pressure may possibly wedge southward on Wednesday to create the possibility for MVFR/IFR ceilings. Conditions should return to VFR by Thursday as the weak wedge erodes quickly. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Heat Advisory until 7 PM EDT this evening for VAZ044>047-058- 059. NC...Heat Advisory until 7 PM EDT this evening for NCZ005-006. WV...None. && $$ SYNOPSIS...PW NEAR TERM...PW SHORT TERM...NF LONG TERM...NF AVIATION...PW

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