Area Forecast Discussion
Issued by NWS Blacksburg, VA

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082 FXUS61 KRNK 230003 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 803 PM EDT Sat Jul 22 2017 .SYNOPSIS... 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. && .NEAR TERM /THROUGH SUNDAY/...
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As of 745 PM EDT Saturday... Have drastically reduced pops per latest radar, satellite, and hires/short term model trends. A weak short wave moved through the CWA earlier this afternoon, to which scattered thunderstorms developed along the Blue Ridge, quickly moved southeast, and dissipated as it moved out of the CWA. Stronger activity associated with a wavy frontal boundary to our north will remain very close to the boundary and gradually work its way south during the night in a much weaker fashion. Have retained chance pops after midnight, but these will likely need to be reduced drastically in the next update if the current and projected trends by short range models (e.g., HRRR) hold true, there may be little overnight until after 08Z, then mostly in the west. SPC indicates that they will remove the SLIGHT RISK in our CWA for tonight with the 01Z update. Confidence in activity for tomorrow is still only in the chance range, much of which will depend on how much cloud cover and convection there is in the morning. Will not make any changes to tomorrow`s pops for now. SPC still holding a SLIGHT RISK for tomorrow. Heat Advisory expired at 7 PM EDT. Will let mid shift decide if another one needs to be issued for tomorrow in the Piedmont in coordination with our eastern/southern neighbors. 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 TUESDAY NIGHT/... 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. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... 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. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/...
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As of 750 PM EDT Saturday... No convection left in the CWA at this time. Meso-high has built across the area and left us with mainly just a high cirrus deck from upstream convection. HRRR suggests little will happen until after 08Z, when some showers/thunderstorms may begin to spread back into the area from the west/northwest. Current thunderstorms to our north extend along a wavy quasi-stationary frontal boundary that will move little overnight. Southward push of convection will be largely from cold pool outflow and density. However, the overnight trends will determine how active Sunday becomes in terms of convection. HRRR, as well as larger synoptic-scale models, through tomorrow afternoon is not excited about much convection in our CWA, largely in part because of downslope westerly winds that develop in the morning in the wake of potential MCV. We could see a situation where clouds and early morning showers relocate to stronger convection in the afternoon mostly across eastern/southern areas. For now, have left VCTS/TS out of the TAFs until there is greater consensus among the synoptic scale and short range models. All this being said, generally looking at a VFR forecast through the TAF valid period. Not expecting fog/low cloud development tonight/early Sunday because of high temperatures today, large T/Td spreads, and extensive mid/high clouds overnight from upstream convection and possible convection later tonight. Winds will be SW-WSW through the period at speeds of 4-6kts overnight and 8-10kts after 14Z Sunday with low end gusts possible at most sites. Medium confidence in ceilings through the TAF valid period. Medium to high confidence in visibilities through the TAF valid period. High confidence in wind speed/direction through the TAF valid period. Aviation Extended Discussion... The cold front currently to our north should be near the NC/VA border by Monday. This leaves a baroclinic zone in or near the area through much of the extended period. Additional upper-level disturbances are progged in northwest flow to impact the area, leaving an unsettled weather pattern in place. The most likely areas to see convection, at least during the first part of the week would be near the NC/VA border, mainly affecting KDAN. Late/night early morning fog can be expected in the usual locations, otherwise outside these concerns and scattered convection, mainly in the south, look for mostly VFR cigs/vsbys.
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&& .RNK WATCHES/WARNINGS/ADVISORIES...
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VA...None. NC...None. WV...None.
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&& $$ SYNOPSIS...PW NEAR TERM...PW/RAB SHORT TERM...NF LONG TERM...NF AVIATION...PW/RAB

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