Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 200817 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 417 AM EDT Wed Jul 20 2016 .SYNOPSIS...
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A weak cold front will remain to the south of our forecast area today with high pressure in control through the remainder of the week. This will result in warm and drier weather, but an isolated shower or storm still cannot be ruled out.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 405 AM EDT Wednesday... Difficult to find exact location of diffuse cold front any more, but based on mean sea level pressure trough it may rn from far southeastern VA into northern NC and then southwest into far northern GA. Surface dew point front may still lie just to the north of our CWA. Still, it is clear much drier air has moved in aloft behind last evenings upper short wave and with mixing during the day should expect the dew point front to shift to the south of the area as well. SBCAPE values may be moderate during much of the morning, but with daytime mixing of drier air these should drop during the afternoon. Therefore, would expect a drier day, but with more sunshine still quite warm, or at least seasonable daytime temperatures. Some very weak convergence in the NW NC mountains and perhaps still close to the frontal boundary may be just enough to squeeze out an isolated storm or two, but anything trying to form will be battling entrainment of drier air aloft so not especially confident in anything forming. Hardly any hi-res models suggest this either. One small concern is that by evening as dew points increase again with loss of mixing that surface- based instability increases again. While there is hard to find any kind of triggering mechanism, any lingering outflow boundary may be enough to pop something but would tend to be weak and shoirt- lived. The NAM is suggesting scattered storms across central part of forecast area by evening but think its low- level moistuire is overdone. However, one or two other hi-res models or ensemble members suggest some signals similar but not as agressive as NAM. Based on this idea, have added a slight chance PoP in basically from ROA southeastward where these models suggest the best potential is, and only from about 6pm through 10pm. There may end up being nothing at all, but feel this pattern can produce isolated overnight weak convection and since just a couple of models hinted at it, felt it worthy of a very small PoP. Otherwise clearing skies again overnight with light winds under influence of surface high pressure. Patchy early morning fog a decent possibility in favored locations and especially if there are any pop-up evening showers which help to re-moisten the ground.
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&& .SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/...
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As of 200 AM EDT Wednesday... During this portion of the forecast a broad upper ridge will be centered over the central portion of the country. The center of this high will very gradually retrograde westward. The result will be a trend towards better chances of disturbances across the Great Lakes region heading southeast towards our region. This looks to happen on Saturday when a cold front works its way into the area and brings isolated to scattered showers to the region Saturday into Saturday night. Prior to this time, precipitation on Thursday and Friday will be limited to primarily isolated orographical activity along the crest of the Blue Ridge. Temperatures will trend warmer through the period with readings on Saturday averaging five to ten degrees above normal. Also on Saturday, the heat index is expected to be in the 100 to 105 range generally along and east of a Lawsonville, NC to Lynchburg, VA line.
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&& .LONG TERM /SUNDAY THROUGH TUESDAY/... As of 230 PM EDT Tuesday... By Sunday the upper pattern will have transitioned to a quasi zonal regime with the jet stream riding well to our north. This will keep us in the heat and humidity through the first part of next week. The zonal flow will result in little push to get fronts trough the region and as a result, a washed out frontal boundary combined with a lee/thermal trof will keep an elevated chance for thunderstorms across the region on Sunday, followed by another weak front moving in from the northwest and continuing our chances for thunderstorms as it washes out over the area Tuesday. Air temperatures and heat index values will remain at hazardous levels on Sunday especially across the piedmont, with only a slight tempering of the heat through the first part of next week. && .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/... As of 155 aM EDT Wednesday... Weak and slowly moving cool front still across central part of Blacksburg forecast area and weak upper level wave exiting the region as well. these both helped to spawn scattered strong late night storms but these have now weakened and moved southeast of the area. Otherwise skies are clearing under mid level dry air and upper ridge. this could result in patchy IFR fog at favored locations before dawn, most notably KLWB and perhaps KBCB, and lower confidence at KLYH and KDAN but they did receive rainfall Tuesday so at least a chance for MVFR fog there before dawn as well. For Wednesday...upper ridge from the central U.S. will continue to build eastward resulting in increasing subsidence. With the front drifting south of the area this should finally yield a mostly convection free day. The main area to watch would be far SW VA and perhaps the NW NC mountains, but not at any of the TAF sites. One or two models, including 00Z NAM, does suggest widely scattered storms again in ther Piedmont but very low confidence in this solution given very dry mid level air and lack of any lifting mechanism unless there are lingering outflow boundaries that may help trigger something. not nearly enough confidence to mention thunder at any TAF sites. Winds will be light northwest through the 06Z to 06Z TAF period, mostly less than 5kts. Extended aviation discussion... Strong high pressure aloft will bridge east across the region Thursday into next weekend. Cannot totally rule out an isolated storm each afternoon/evening through the period but appears overall VFR outside of the typical late night valley fog in spots. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/SK NEAR TERM...RAB/SK SHORT TERM...DS LONG TERM...MBS AVIATION...JH/RAB/SK

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