Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 231424 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1024 AM EDT Sun Apr 23 2017 .SYNOPSIS... Expect wet weather at least through Monday night, with surface low slowly moving from northern Georgia this morning, to the NC/SC coast by Tuesday morning, while upper low slowly traverse the same general area. && .NEAR TERM /THROUGH TONIGHT/...
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As of 1024 AM EDT Sunday... The cold front is pushing south and cool wedge is in place resulting in clouds and cooler temperatures. Made some minor changes in temperatures this morning using the GLAMP, with little change in temperatures throughout the day with highs generally from 50 to 55 across the area. Rain cooled areas in the southwest mountains may stay in the low 40s. Low pressure in Georgia will move southeast into South Carolina tonight. This system will generate rain across our area today into Monday. Rain will be heavy at times and a flood watch remains in effect until 8pm Monday. Current radar shows rain in the southwest moving towards our area. Rain will become widespread this afternoon into tonight. more changes later this morning... Previous morning discussion... As of 734 AM EDT Sunday... Not much on radar at the moment but upstream area of rain coming together over Eastern TN, and look for the southern county warning area to fill back in with rain as upper divergence shifts to the region after 10am. No other changes needed to the forecast. Expect a lull in heavier showers this morning as we wait for the positive tilt trough over the Mid-MS valley shift east and become more neutral then negatively tilted by tonight, while deepening. For this morning, pockets of deep moisture convergence situated from the southern Appalachians northeast to the VA piedmont will continue the shower threat here with less to little coverage over Southeast WV to the southern Shenandoah Valley. Some fog at the higher elevations is likely with low clouds in place. Better lift/jet dynamics/upper difluence start to move into southern forecast area after mid morning, then shield of rain stays elongated from Southeast KY/Eastern TN east to the VA/NC piedmont with models varying on where the heavier rain falls, but based on high-res runs and track of sfc/upper low, the flow into the southern Blue Ridge favors higher totals here, this afternoon/evening then expanding over the Piedmont tonight. Convection should be limited with stable airmass under high pressure wedge, but cannot rule out some elevated convection near the NC piedmont south of Danville/South Boston, but overall not enough support for thunder. Per models, and not expecting deeper convection, hourly rainfall rates should be limited, however, still after the past couple of days of scattered to numerous showers, and adding on another 1-2 inches, with possibly up to 3 inches near/east of the Blue Ridge south of Roanoke to the NC piedmont, the flood threat remains for creeks/streams and rivers. The flash flood threat will be isolated but cannot rule out some pockets across the southern Blue Ridge this evening. So in essence after somewhat of a quiet early morning, look for rain to pick up late this morning and especially this evening and overnight, when the flow in the low levels increases out of the east. Late tonight, some potential for dry slot to work toward the Mountain Empire before the easterly fetch off the Atlantic pulls rain back to the west Monday. Temperatures during this time will be cool with upper 40s to lower 50s for most, with coolest readings along the Blue Ridge south of Roanoke to Boone. Rainfall overnight will keep temps from falling much but expect 40s areawide.
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&& .SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/... As of 400 AM EDT Sunday... Vertically stacked cyclone will continue to slowly pinwheel into central Georgia Monday into Monday night. There still is a good transport of moisture in southeast flow Monday with PWAT values on the order of 1.25" along/east of the Blue Ridge and into the Piedmont, though the highest values are more focused into eastern sections of North Carolina and eastern Virginia. In addition, stable thermodynamic profiles owing to residual wedge should keep rainfall rates lower/more gradual and also likely mitigate any thunder. Steadiest rainfall and highest PoPs Monday into Monday evening will also be more focused in the southeast upslope areas in the Blue Ridge foothills and eastward into the Piedmont, with relatively lower (Likely tapering to Chance) with more shadowing into southeast West Virginia and adjacent sections in southwest Virginia. Will also start to see increasingly more breezy northeast to north winds particularly in eastern sections later Monday into Monday night. This is due to a strengthening pressure gradient between high pressure over the Northeast states and a sub-1000 mb low over the Carolinas, with northerly isallobaric component also helping to keep breezy conditions going even into overnight. Highs are only in the 50s tomorrow and fall to lows in the upper 40s to low 50s. By Tuesday, upper low begins to undergo deamplification with an eventual track along the Carolina coastline. As the upper low pivots northward on Tuesday, we should see a northward commahead rain band brush our Piedmont and Southside counties during the morning hrs, with accumulations here tending to be two tenth of an inch or less. Lighter showers in central and western counties are anticipated. Forcing for precipitation then becomes more nebulous through the afternoon with a taper-down in PoPs areawide to dry on Tuesday night. A little less cloudiness in the afternoon should help to boost highs back into the mid 60s to near 70 with lows mid 40s to lower 50s. We return to sunnier, milder and drier weather looking ahead to Wednesday. The upper low that plagues our weather loses its influence and pivots into New England, with mid-level ridging building out ahead of more unsettled weather that looks to evolve across the central Plains and upper Mississippi Valley. Southwesterly warm advection pattern begins and temperatures then return back into the upper 70s to a few 80s. && .LONG TERM /THURSDAY THROUGH SATURDAY/... As of 400 AM EDT Sunday... The long wave trough deepens in the central United States putting the region in broad southwest flow Thursday through Saturday. Models were showing varying degrees of strength of the southeast ridge. Low pressure tracking northeast into the Great Lakes will move a front into the Ohio and Tennessee Valleys on Thursday. This boundary stalls on Friday before another low moving out of the southern Plains pushes a warm front into the Ohio Valley on Saturday. This pattern keeps the rain potential to the west of the Mid Atlantic states. Temperatures will be above normal Wednesday and Thursday. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/... As of 730 AM EDT Sunday... Not too much change to the forecast and overall keeping sites under VFR through the period. Expect rain to overspread the area from southwest to northeast after 14z with moderate to heavy rain at times, especially along and south of ROA/BCB toward TNB/MWK/UKF and eventually DAN. No thunder expected at this time, so mainly looking MVFR to IFR vsbys in rain, with VFR at times, while cigs fluctuate between high end MVFR to IFR, with higher ridges more prone to lower cigs/vsbys thru the period. Winds will be out of the east mainly around 10kts all sites, some gusts to 20kts possible near ROA/BCB/LYH. Extended Aviation Discussion... Poor aviation conditions expected to continue through Monday, and at times into Tuesday, thanks to the slow moving upper low and attendant sfc system. Look for gradual improvement sometime Tuesday from west to east with better flying wx for by midweek, though another front may bring scattered showers/storms toward late Thursday in the mountains. && .HYDROLOGY... As of 330 AM EDT Sunday... No changes to the flood watch, with still some model differences in placement of highest rainfall threat. High-res models and analogs along with pattern recognition favor the southern Blue Ridge from Roanoke to Boone, east to the piedmont of VA/NC as those areas which appear to be in line to receive 2-3" today through early Tuesday. This amount of rain combined with the 1 to 2+ inches that has already fallen since Friday should lead to hydro issues on rivers, as well as smaller creeks and streams. Looking at the analogs this pattern favors April 5th, 1993, and March 27th, 1993 which produced some minor to moderate flooding along portions of the Dan and Roanoke River mainly downstream of Danville and Altavista. Still will have to see how this sets up as we had been dry prior to this event. WPC has moderate risk of FFG exceeded over the southern Blue Ridge. As mentioned in the near term, deep convection seems limited thereby will have to rely on upslope component to enhance rainfall rates, so isolate flash flooding is possible, but more longer term >6hr flooding is more likely. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Flood Watch through Monday evening for VAZ007-009>018-022-023- 032>034-043>046-058-059. NC...Flood Watch through Monday evening for NCZ001>006-018>020. WV...Flood Watch through Monday evening for WVZ042. && $$ SYNOPSIS...WP NEAR TERM...KK/RAB/WP/SW SHORT TERM...AL LONG TERM...AL/AMS AVIATION...AMS/RAB/WP HYDROLOGY...KK/MBS/WP

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