Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 150800 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 400 AM EDT Tue Aug 15 2017 .SYNOPSIS...
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Upper disturbances move over the area today, with a stalled frontal boundary in place. This front shift southeast tonight, with high pressure shifting over the Mid-Atlantic Wednesday. A cold front moves from the Midwest Thursday into the Appalachians Friday.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 330 AM EDT Tuesday... Scattered to numerous showers early this morning from WV/SW VA east to the piedmont. This is occurring along sfc boundary with wave of low pressure over KY/TN, interacting with pwats over 2", as well as a couple of vorts from TN to western NC. Will see greatest concentration of showers over the piedmont of VA and from the Mountain Empire north toward Greenbrier this morning. Overall high-res solutions painting a wet morning for most of the forecast area. Once main axis of upper level energy shifts east of the mountains this afternoon, should see decreasing threat over the mountains, then this evening in the east, though some of the high- res models pushing batch of showers east of the WV mountains/far SW VA by 12z this morning. Given radar trends, should be close. Nonetheless 50 pops to 80 pops warranted with highest along/east of the Blue Ridge. Again, hedging on whether we get sun this afternoon or not, and high-res models showing some breaks, so instability should increase with help of upper vort to allow thunderstorms to be isolated to scattered, or embedded in the main area of showers. Should see skies clearing tonight from the northwest as deeper moisture shifts to the east/southeast, though how far given Hurricane Gert further east slowing thing movement of the front down. Gert should be pushing back out toward the northeast late tonight allowing this to happen. Another shortwave skims across the TN/NC tonight which may keep showers isolated along/south of the NC/VA border. With clearing skies, light winds, and moist ground look for more fog late tonight into Wed morning. Highs today a few degrees warmer than Monday since wedge erodes, but still a few degrees below normal, with mid 70s to around 80 mountains, to lower to mid 80s east. PWATS are expected to drop off some late tonight, and should see lows still held up some, with lower to mid 60s mountains, to upper 60s to around 70 east of the Blue Ridge.
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&& .SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
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As of 245 AM EDT Tuesday... Another surface high will drift over the northern Mid Atlantic Wednesday and wedge south into the Carolinas Wednesday night. Upslope flow across North Carolina High Country may be enough to spark some storms late in the afternoon. Weak steering flow will have any storms drifting east over the foothills in the evening, then fading by sunset. Storms are also possible along the SW VA Blue Ridge in the afternoon. However, mid level cap is lower, therefore storms will have a tough time developing or be short-lived. The wedge boundary should not advance into the area until the evening, therefore temperatures Wednesday will warm to or a few degrees above normal. Shallow wedge comes sliding across the region Wednesday night. Easterly flow will bring some low deck clouds into the region, but models look to dry and stable for any precipitation overnight. A cold front is expected to move from the Midwest Thursday to the Appalachains Friday. Pressure falls Thursday will erode the wedge by the afternoon. Prefrontal short waves will then bring the first round of storms into the region Thursday afternoon and evening. The next round will be with the passing of the cold front Friday. Thursday looks to be the better of the two day for strong to severe storms to pass over the area. If Thursday`s activity is lack luster, then Friday may be busy. Temperatures Thursday will warm above normal with mid to upper 80s west of the Blue Ridge to the lower 90s east. Similar temperatures expect Friday but could be cooler depending on timing of the frontal passage.
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&& .LONG TERM /FRIDAY NIGHT THROUGH MONDAY/... As of 312 PM EDT Monday... Cold front finally moves across the forecast area Friday night. A considerable amount of variance exists in the 12z GFS and ECMWF solutions for the weekend, particularly on if the front makes a full clear across VA or if it hangs around/stalls and picks up tropical moisture keeping our eastern and southern counties wet. Adding to this uncertainty is the timing of a mid-level disturbance in the northern stream across the Great Lakes region. Therefore, kept at least 15-30% PoPs east of the Blue Ridge for the weekend until less variability in guidance becomes apparent. Stayed close to a blend of guidance for highs and lows which keep temperatures near typical mid- August levels. A potentially warmer period is indicated by the GFS and ECMWF early next week as a broad heat ridge dominates much of the Plains and into the Ohio Valley. && .AVIATION /08Z TUESDAY THROUGH SATURDAY/... As of 130 AM EDT Tuesday... Poor flying conditions expected across the entire region this morning with periods of showers heavy at times, especially in the Danville area. When showers occur vsbys could drop to IFR 1-3sm, with cigs around 1-3kft. With lighter showers or none, expect some vsbys to sink below 1sm, and confidence not high enough to go this direction except perhaps LWB/BCB/BLF. Cigs will also drop below 1kft. Overall sub MVFR with LIFR thru at least 12-14z, then should start to see cigs/vsbys edge up to MVFR at all sites in the 14z-17z time frame, then VFR afterwards, except lingering MVFR through mid afternoon at LYH/LWB/BCB. Greatest rainfall threat looks to occur through 15z today, then afternoon coverage looks less in the mountains, with better coverage in the piedmont. For now kept VCSH this afternoon east of the mountains, however, thunder is possible. Extended Aviation Discussion... Widespread fog is again expected late Tuesday night as we clear out some,with dense fog possible. Wednesday into Thursday the frontal boundary to our south will meander north and south for a bit until such time the departure of Hurricane Gert allows the front to be shunted to the southeast. While the front is in our proximity, daily scattered precipitation and rounds of sub-VFR conditions are probable. Late night/early morning mountain and river valley sub-VFR fog will be possible. Friday into Saturday, we look to our northwest for our next approaching upper level system. This one will bring a cold front into and through the area Friday night. Look for an increase in precipitation on Friday with storms possible during the afternoon and evening. Sub-VFR conditions will accompany the heavier showers and storms, and also persist in the form of late night and early morning fog heading into Saturday morning. && .EQUIPMENT... As of 755 PM EDT Saturday Aug 12th... KFCX doppler radar will continue to be down for the rest of the month due to a failing bull gear. It will only be operational during this time frame for brief periods if an imminent significant widespread severe weather and/or hydrologic event occurs. Operating the system for any amount of time until the bull gear is replaced risks a catastrophic failure that would further extend system downtime. From the 17th through the 27th the radar will most likely be down completely as the repairs are expected to be made during this period. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...DS/WP NEAR TERM...WP SHORT TERM...RCS LONG TERM...AL AVIATION...AMS/DS/WP EQUIPMENT...RAB/WERT

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