Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 191745 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 145 PM EDT Wed Jul 19 2017 .SYNOPSIS... A weak upper low over southeast Virginia will move south along the North Carolina and South Carolina coast line through Friday. High pressure aloft will build east from the Midwest toward the southern Appalachians and Southeast U.S. through the weekend. A cold front will move southeast into the region from the Great Lakes late in the weekend. && .NEAR TERM /THROUGH TONIGHT/...
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As of 100 PM EDT Wednesday... Latest satellite imagery and radar returns are indicating the most probable location of isolated showers this afternoon will be along and near the crest of the Blue Ridge, and near Bluefield, WV, south into part of the Mountain Empire part of southwest Virginia, and the Northern Mountains and Foothills of North Carolina. Have updated the forecast accordingly. Have also tweaked hourly temperature, dew point, sky cover, and wind/gusts based upon the latest observations and expected trends through the afternoon. Have lowed the forecast high temperature for the Lewisburg, WV region given lengthy duration of fog this morning kept conditions a bit cooler their longer than originally anticipated. As of 940 AM EDT Wednesday... Fog over parts of the New and Greenbrier River Valleys is starting to erode, and that trend is expected to continue. Anticipate little if any fog remaining across this region by 1100 AM EDT. Have reflected the forecast accordingly. Am making no significant changes at this time to the remainder of the forecast for today. Have made minor tweaks to hourly temperature and dew points based upon the latest observations and expected trends into the early afternoon. As of 330 AM EDT Wednesday... Showers and thunderstorms, associated with a weak upper low now located over southeast Virginia, dissipated quickly after sunset with no convective activity left in or near the CWA at this hour. The upper low will drift further south along the North Carolina coast today and tonight. The associated cold pocket aloft will dissipate with 500mb temps warming from -10C yesterday to around -6C by the end of the day today. Lapse rates will be markedly weaker and overall the atmosphere much more stable. All this will be the result of the upper low moving away and heights building eastward from the Midwest where a strong 597dm upper ridge is located. Confidence in convection today is low. Situation is entirely different than yesterday and none of the models really indicating much occurring at all. HRRR and NSSL WRF very quiet with little to no convection indicated through the end of its cycle. Nonetheless, not comfortable with temperatures warming into the 90s and dewpoints well into the 60s of completely unmentionable pops, so have included a 15% pop for all areas east of the Alleghany front. Feel that areas along and west of the Alleghany front will be closer to the upper high and too stable for convection. The Piedmont and/or along the Blue Ridge should be the most favored areas for convection today. Then again, I could also see a scenario with no convection at all. It is rare to have two back-to-back days like yesterday and again it is worth noting that the synoptic situation is far from favorable for such today compared to yesterday. Temperatures will be on an upward trend the next couple of days as the upper ridge builds east. 850mb temps have been hovering near or just below 20C. These will be creeping up toward +22C to +24C over the next couple of days. Not enough rise today to really be reflected in the max temps, so have only raised them a degree or two in most areas. This will yield low 90s Piedmont to mid 80s west, except upper 70s higher elevations of the mountains. Overnight lows Thursday morning should be considerably warmer than this mornings temps as a consequence of the lack of convection to lead off with a rather cool evening. Lows Thursday should range from the lower 70s Piedmont to the lower and mid 60s across parts of the Greenbrier and New River Valley as well as mountain valleys throughout the west. Finally, do expect fairly widespread areas of dense fog this morning from late day rain Wednesday and calm winds, clear skies, and effective radiational cooling this morning. Fog will likely be less widespread Thursday morning with the lack of late day rainfall and warmer overall minimum temps, hence greater T/Td spreads.
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&& .SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/... As of 230 AM EDT Wednesday... Quieter yet hotter weather in store Thursday, as dome of high pressure slides east from the southern Plains and Mid-Mississippi Valley. Still enough low level convergence where an isolate storm could pop up along the higher terrain in the afternoon but most will be dry. Temperatures should peak out in the mid to upper 80s across the mountains, to the lower to mid 90s east. Dewpoints in the 60s should keep heat indices mostly in the 90s east. Friday, the upper center of the high remains over the TN valley, while southern belt of westerlies stays situated from the northern Plains, east to the mid-Atlantic. Will have to watch for convection firing upstream and density of an MCS being able to propagate southeast into our area. Most of the 0z models are favoring some convection sliding toward the northern CWA in the afternoon, roughly from the Greenbrier valley of WV eastward toward Lynchburg. Not too confident given the flow aloft and the warmer temps aloft with the ridge in place, so will have mainly slight chance pops in the mountains, to low chance over the Alleghanys, while keeping most of the piedmont/foothills south of Roanoke/Lynchburg dry. Friday`s highs should be a few degrees warmer if we have no convective blowoff, with upper 80s to lower 90s in the mountains, to mid to upper 90s in the piedmont/foothills/Roanoke. Dewpoints creeping up will make this the day where heat indices could exceed 105 degrees in some of the piedmont area. Heading into Saturday, 5h heights fall slightly with southern belt of westerlies dropping toward the south into Virginia. This combined with an frontal boundary across the mid-Atlantic and upstream convection should allow for at least outflow driven convection to fire during the afternoon. Highs again will be dependent on clouds, but should be a degree or two cooler than Friday but hot nonetheless, with mid 80s to near 90 west, to mid to upper 90s east. Again with dewpoints near 70, heat indices could threaten 105 degrees along/east of Highway 29 Lynchburg/Danville south into Yanceyville. Any convection Friday-Saturday should weaken/dissipate during the nighttime hours, while lows stay elevated in the upper 60s to mid 70s. && .LONG TERM /SUNDAY THROUGH TUESDAY/... As of 315 PM EDT Tuesday... Very warm/hot weather expected to persist through much of the long-term forecast period. Weak upper closed low expected to drift west into AL over the weekend, then shear slowly northeast back toward the southern and central Appalachians by early next week. Meanwhile, a series of short wave trofs in the northern stream are forecast to scoot east through the Great Lakes, with the strongest on Sunday into Monday likely to push cool front/baroclinic zone south toward or through the Blacksburg forecast area later Monday or Monday night. Whether the surface front can progress this far south while pushing against a strong Bermuda high pressure system still remains somewhat in question, but the frontal proximity, combined with at least some moisture streaming back northeast in advance of southern closed/shearing low should support a slowly increasing threat for mainly diurnally-driven showers/thunderstorms into portions of the Blacksburg forecast area, especially in the mountains (Saturday) and into most areas Sunday into early next week as the front nears or moves southeast through the region. Little overall change in airmass expected until the possible frontal passage - with a continuation of relatively hot days with warm nighttime lows, but with only a very limited threat for any record breaking readings. Cooler air may arrive by Tuesday, driving temperatures back down 5-7F and closer to seasonal levels. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
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As of 130 PM EDT Wednesday... VFR conditions are expected to prevail the remainder of the afternoon through the evening hours. The exception will be very isolated, brief, sub-VFR conditions under any of the heavier showers or storms that develop this afternoon. Overnight, anticipate a return of fog to mainly the mountain and and river valleys. MVFR visibilities are anticipated where the fog develops with localized LIFR/IFR visibilities. LIFR/IFR stratus, or vertical visibility, is also anticipated in conjunction with the fog, comparable to reality from this morning. Most of the sub-VFR conditions will improve to VFR by 14Z/10AM Thursday. Winds through the forecast period will mainly be light and variable or calm. Confidence levels are high regarding the wind through the 24 hour TAF period. Confidence levels regarding ceiling and visibilities are high during the daylight and evening hours. Confidence is moderate late tonight into early Thursday morning. Aviation Extended Discussion... Mainly VFR conditions are expected through Sunday as upper level ridging allows for at best isolated to scattered afternoon and evening showers and storms. Brief, sub-VFR conditions will be possible with the heavier showers and storms. Late night/early morning sub-VFR fog will be possible, mainly in the mountain and river valleys. A cold front will move into the region Sunday night into Monday. Look for an increase in convection, and better chances of sub- VFR conditions in association with convection along the front. Overnight fog will be more likely Sunday night into Monday morning. Confidence of all weather parameters is moderate during the extended portion of the forecast.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RAB NEAR TERM...DS/RAB SHORT TERM...WP LONG TERM...WERT AVIATION...DS

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