Area Forecast Discussion
Issued by NWS Blacksburg, VA

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770 FXUS61 KRNK 260948 CCA AFDRNK Area Forecast Discussion...Corrected National Weather Service Blacksburg VA 438 AM EDT Fri May 26 2017 .SYNOPSIS... Low pressure will exit to the northeast of the region this morning followed by high pressure that should build in by afternoon bringing drier weather on gusty westerly winds. The high weakens overnight allowing a warm front to lift north across the region before stalling. Weak disturbances will ride east along this boundary resulting in a return to periodic rounds of showers and thunderstorms for the holiday weekend. && .NEAR TERM /THROUGH SATURDAY/... As of 300 AM EDT Friday... Upper low to the northeast will continue to pull away this morning allowing brief shortwave ridging to slide east as the associated surface high builds south of the area. This should bring a period of drying as the flow turns more westerly and decent subsidence arrives per drying seen on water vapor this morning. However expect will see low clouds persist far west through around midday per northwest upslope including trapped low level moisture with a few light showers/sprinkles possible. Thus will keep some low pops going before drying wins out and all break into sunny skies this afternoon. Winds to remain gusty with some enhancement due to heating/mixing so will keep the impact based wind advisory in place this morning. Otherwise more insolation along with eastern downsloping and exodus of the 850 mb cool pool should allow for much warmer highs, with readings rebounding back into the 70s most spots and perhaps around 80 southeast. Upper ridge starts to flatten overnight in response to shortwave energy passing north which will allow a warm front to shift north passing west of the mountains late. An initial belt of stronger winds aloft will ripple a weak sheared mid level impulse east along the boundary with this feature approaching by early Saturday. This along a baroclinic zone separating much warmer/juicier air to the southwest and more of a capped environment to the east. Latest guidance has a cluster/band of showers zipping east with this wave perhaps reaching the far northwest counties by daybreak Saturday within the sharp westerly flow aloft. However latest soundings still indicate some residual dry air aloft which should help to weaken coverage. Thus only running with low chances northwest third late. Otherwise more clouds north and remaining mostly clear south overnight. Lows mostly in the 50s but could rise late including the ridges where may stay above 60 as warm advection aloft quickly returns. Overall reprieve from persistent rainfall will be short as the boundary stalls just northwest of the area Saturday with an impressive return of moisture per jump in dewpoints and subsequent humidity by afternoon. In return, models indicate quite an unstable environment developing with MLCAPE values better than 1500 J/KG given heating under decent jet energy aloft ahead of a secondary wave aloft arriving over the northwest late. This impulse could lead to an organized area of convection riding east behind the initial wave with fast moving storms impacting espcly northern sections, and perhaps elsewhere pending organization under the fast flow aloft. Therefore will keep likely pops northern sections with high/decent chance pops elsewhere in the afternoon including severe mention in the HWO per slight risk in the SWODY2 attm. Will feel quite warm given the coolness of late as highs under strong 850 mb warming look to zoom back well into the 80s east, and around 80 west pending early debris clouds. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... As of 415 AM EDT Friday... Very active weather will continue through the period as a series of upper-level disturbances track along/near a baroclinic zone/frontal boundary that will be draped from west-east bisecting the forecast area. Very unstable air will persist south of the front Saturday night and continue Sunday as well. Ongoing thunderstorm activity Saturday evening could well linger into much of the night as the air mass south of the frontal zone remains warm and unstable. Some of these could continue be strong to severe, although the greater threat for severe will be during the early part of this period, namely Saturday evening, or before during Saturday afternoon. The axis of stronger thunderstorms is expected to shift slightly further south for Sunday, more into far southern VA and northern NC, as the boundary sags further south in response to upstream troughing and convective outflowboundaries from Saturday. Thermodynamic and dynamics parameters suggest strong instability and moderate shear. SPC continues to outlook much of this time frame in a Slight Risk for severe. Temperatures Saturday and Sunday will be warmer than in recent days, with widespread 80s outside the mountains, where highs will mostly be in the 70s. However, these warmer temperatures will not be sustained long as showers, thunderstorms, and associated clouds overspread the area during the afternoon. Low temperatures will be on the mild side, mostly in the mid 50s to lower 60s. For Monday, the upper low remains well to the northwest keeping a cyclonic flow in place across the region. The aforementioned surface boundary will be push a little further south and is expected to lie somewhere across the southeast states toward the VA Tidewater region. Scattered convection will remain in the forecast as another upper trough sweeps into the region from the northwest. Instability is less impressive with this activity, but with cooling temps aloft and good dynamics, even a few strong to severe thunderstorms could even occur within this time frame. Temperatures are expected to remain similar to what noted above, namely lows in the 50s west to 60s east with highs in the 70s west to the 80s east. && .LONG TERM /TUESDAY THROUGH THURSDAY/...
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As of 430 AM EDT Friday... Remaining active and wet more than dry. An upper-level low will persist across the Great Lakes region with a series of embedded disturbances rotating through the upper low keeping the threat for showers and thunderstorms going in our area. In addition, we will have yet another baroclinic zone, this time stalled just to our south. At this point, Thursday appears to be the most volatile day weather wise with widespread thunderstorms and heavy rainfall possible. Temperatures during the period will remain relatively close to climatological normals. Look mostly for highs in the 70s west to 80s east and lows in the 50s west to the 60s east.
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&& .AVIATION /08Z FRIDAY THROUGH TUESDAY/... As of 105 AM EDT Friday... Upper low will gradually lift northeast and away from the area through Friday morning. However northwest flow around this system will continue to result in a few showers across the northwest mountains in the vicinity of KLWB/KBLF into early Friday. A broad area of IFR/MVFR cloud cover will remain over the mountains overnight with improving conditions east of the Blue Ridge where VFR cigs to clear skies can be expected. Visibilities will mainly be VFR, but pockets of MVFR visibilities are possible across western slopes. Wind gusts across the higher elevations will be in the neighborhood of 25 to 35 kts through Friday afternoon. These winds will mix down to the lower levels at times with heating during Friday. Extended Aviation Discussion... We will transition back into a wet pattern over the weekend as a frontal boundary enters and stalls over the area. A series of disturbances will bring showers and storms to the area. Anticipate at least some periods of sub-VFR conditions into Monday. The coverage of showers and storms should decrease by Tuesday resulting in more widespread VFR toward the middle of next week. && .HYDROLOGY... As of 110 AM EDT Friday... Small streams and creeks have been receding and most are below flood stage. However most will stay elevated into Friday as significant runoff continues and crests move down the mainstem rivers. Good drying on Friday should also aid in helping levels drop fall a bit quicker. We are in a river flooding scenario for portions of the Roanoke and Dan River basins with at least minor flooding on some of the downstream sections such as Randolph and South Boston likely to persist into the weekend. The New River and Greenbrier river are expected to stay below flood stage with near bankfull levels on the James especially downstream from Buchanan into Friday. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Wind Advisory until noon EDT today for VAZ007-009>020-022>024- 032>035. NC...Wind Advisory until noon EDT today for NCZ001-002-018. WV...Wind Advisory until noon EDT today for WVZ042>044-507-508. && $$ SYNOPSIS...JH NEAR TERM...JH SHORT TERM...RAB LONG TERM...DS/RAB AVIATION...DS/JH/RCS HYDROLOGY...WP is the U.S. government's official web portal to all federal, state and local government web resources and services.