Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 171515 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1115 AM EDT Tue Apr 17 2018 .SYNOPSIS... The combination of high pressure well south of the region and low pressure to the northeast will maintain a gusty northwest flow across the region today and tonight. The next chance of showers arrives late Wednesday as low pressure moving through the Great Lakes pushes a cold front through the region. Strong high pressure follows the front with another round of gusty winds for late in the week. && .NEAR TERM /THROUGH TONIGHT/...
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As of 1115 AM EDT Tuesday... Back edge of extensive area of clouds lifting rapidly northeast on nose of strong warm advection zone, and expected to clear much of the forecast area early this afternoon. Will make some adjustments to current and near-term hourly temperatures to reflect slightly cooler readings initially with respect to previous forecast in areas that still have cloud cover, but temperature trend back to forecasted highs still seems likely once strong insolation begins as cloud cover retreats. Also, depth of moist layer no longer supportive of any additional accumulating snow across the higher terrain of western Greenbrier County, WV, so have allowed Winter Weather Advisory for that area to expire. Increasing insolation with clearing skies will help maintain sufficient mixing/momentum transfer over the southwestern mountains to warrant continuation of existing Wind Advisory. As of 915 AM EDT Tuesday... Temperatures have risen above freezing across much of southwestern sections of the Blacksburg forecast area excluding the higher ridges, and also east of the Blue Ridge. Have therefore allowed Special Weather Statement for Black Ice to expire across the southwest - and have allowed the Frost Advisory to expire across the foothills and Piedmont. Otherwise, no changes needed to the forecast at the present time. As of 300 AM EDT Tuesday... Large upper low to finally lift out to the northeast today with one final shortwave progged to slide through the region early this morning. This may allow for another quick burst of snow showers over the west so will keep the going winter weather advisory in place mainly for impact given temps below freezing for the morning rush. Otherwise will cover elsewhere with a SPS if needed. Other bigger concern remains with the strong winds across the ridges as guidance suggests ongoing stronger speeds due to subsidence within lowering inversion levels behind the passing wave from earlier. Once this passes expect may see some dropoff in the gradient before deeper mixing takes shape by afternoon when speeds may increase again. However this during a transition to warm advection aloft as weak ridging develops so could offset higher winds reaching the ground to some degree. Thus will continue with the current advisory and allow the dayshift to expand if needed. Frost also looks quite iffy east given clouds/mixing and dryness but since have a few locations that are near freezing will let the headline ride at this point. Otherwise looking at another breezy/windy day with decreasing clouds by afternoon and some surge in temps as a quick transition from very cold 850 mb temps to much warmer aloft takes shape this afternoon. This could quickly push highs well into the 50s/60s southern half, while the north remains in the 40s northwest to mid 50s northeast where still under the edge of the thermal cool pool aloft. Combination of shortwave ridging and increasing warm advection to return overnight within continued strong northwest flow aloft. However with more of a warm advection regime aloft, not expecting winds to mix down as much overnight with latest forecast soundings showing higher speeds trapped above a rather high inversion. Therefore appears winds should diminish rather quickly after sunset and actually become light in spots outside of the ridge tops overnight. Does appear will have some jet induced mid/high clouds sliding in from the west overnight with a decent setup for mountain wave clouds by daybreak. Therefore clear to partly cloudy but dry overnight. This cloudiness should also act to hold temps up as well with lows mostly 40s south to 30s north including the deeper valleys where could sneak down to around freezing west.
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&& .SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/... As of 415 AM EDT Tuesday... A relatively quiescent period, although a progressive series of vigorous upper lows will continue to track in a zonal fashion across the U.S. during the period. The first such system will track across the upper Midwest into the Great Lakes Wed-Thu. The main impact of this system on our CWA will be to bring us another period of strong/gusty west to northwest winds, another surge of cold/sub-freezing air, and snow showers to the mountains. 850mb temperatures on a roller coast from -8C today to +12C Tuesday and then back to -8C on Wed. By far, however, the biggest concern with the next weather system will be strong northwest winds Wed night into early Friday, most likely requiring a Wind Advisory for much of that period with later forecasts. The strongest winds will again be along the Blue Ridge. The combination of strong upslope flow and significant CAA Thursday into Thursday night will likely bring another period of snow showers to the Alleghanys, possibly into southwest VA and northwest NC as well, with minor accumulations of snow again possible, mainly in western Greenbrier county. Surface temperatures will follow the roller coaster of the 850mb temps and progression of low pressure areas with highs in the 60s and 70s Wednesday, dropping back only to the 40s and 50s for Thu and Fri, warming back into the 60s for the weekend. This period should be relatively benign with no significant rainfall, winter weather, or severe storms. && .LONG TERM /SATURDAY THROUGH MONDAY/... As of 425 AM EDT Tuesday... The focus during this period will be on a vigorous southern stream closed upper low tracking from Texas into the southeast states over the weekend. Latest model trends have shifted the track of this system quite a bit to the south, thus that minimal effects are felt much north of NC. However, the trend with later model runs is often to shift the track of the system back to the north. For now, pops have been decreased over the weekend and also mentionable pops have been kept further south closer to the NC/VA/TN border than were previously advertised. We will need to keep a close eye on this system, because a southern track with the cold air mass residing over the eastern U.S. prior to its arrival could bring accumulating snow to the region. While increasingly unusual this late in the season, it is not impossible, although more likely in the higher elevations across the west than other areas. More than likely outside the highest elevations, it would just be a cold rain. Confidence in any one solution for the weekend at this point is low. Overall, residual Canadian air, 850mb temps no warmer than about +6C, and cloud cover/possibly precipitation will hold temperatures around 5-10 degrees below normal during the period. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... As of 710 AM EDT Tuesday... Split in low clouds between VFR cigs out east and MVFR/ocnl IFR continues along the Blue Ridge this morning with sporadic snow showers/flurries in spots around KBLF/KLWB. Expect this trend to continue this morning before winds turn a bit more westerly allowing drying to take shape through the afternoon. This should bring most locations back up to VFR this afternoon. Winds will remain an issue through the day espcly across western locations where gusts may exceed 40 kts at times during deeper mixing this afternoon. VFR should prevail overnight with some influx of mid/high cloud canopy during the evening and perhaps a period of sub-VFR lower cigs around KBLF late given upslope flow. Surface winds should be lighter except along the ridges where gusts to 30 kts may still occur. Extended Aviation Discussion... Overall conditions Wednesday VFR, although there will continue to be a gusty southwest wind ahead of yet another approaching cold front. Next front arrives Wed night-Thu with a chance of showers, with gusty winds and sub-VFR cigs again Thursday in the mountains. VFR returns Friday although gusty northerly winds to persist as high pressure slowly builds in from the northwest. Winds should diminish on Saturday with VFR continuing to start the weekend. && .RNK WATCHES/WARNINGS/ADVISORIES...
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VA...Wind Advisory until 8 PM EDT this evening for VAZ015>017-022. NC...Wind Advisory until 8 PM EDT this evening for NCZ001-002-018. WV...None.
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&& $$ SYNOPSIS...JH NEAR TERM...JH/WERT SHORT TERM...RAB LONG TERM...RAB AVIATION...JH/PM

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