Area Forecast Discussion
Issued by NWS Blacksburg, VA

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331 FXUS61 KRNK 230843 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 443 AM EDT Sun Apr 23 2017 .SYNOPSIS...
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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.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 340 AM EDT Sunday... 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/...
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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.
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&& .LONG TERM /THURSDAY THROUGH SATURDAY/...
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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.
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&& .AVIATION /08Z SUNDAY THROUGH THURSDAY/... As of 140 AM EDT Sunday... Continued to see poor flying conditions this period, but some lull in showers occurring this morning as main batch heads to the piedmont. With a very moist airmass have some fog issues, especially BLF where it could get dense at times. Overall leaning toward less pessimistic but still sub-VFR through the morning, where vsbys/cigs vary from LIFR to low end MVFR. During Sunday should see uptick in rain again, especially south of a BLF-LYH line. Some heavier downpours likely, but thunder threat is limited. Look for IFR-LIFR cigs generally in place at all TAF sites through the Sunday afternoon and evening. Visibilities will be dependent on areas of heavier rainfall, but prevailing MVFR visibilities in -RA/RA, with periods/pockets of IFR visibilities. Winds will be NE 7-10kts with low end gusts likely across the Piedmont through the TAF valid period. Extended Aviation Discussion... Poor aviation conditions expected to continue through Monday. Some improvement will begin late Monday, but more likely into Tuesday as the upper low moves northeast of the area and the surface winds come around to the northeast as opposed to the northeast. This will allow ceilings to improve to MVFR and visibilities to VFR as the rain comes to an end or at least becomes much more showery in nature. VFR conditions are expected Wed-Thu as high pressure, but surface and aloft, build over the area. Another weather system will bring showers and possibly thunderstorms into the area late in the week. && .HYDROLOGY...
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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.
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&& .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...RAB/WP SHORT TERM...AL LONG TERM...AL/AMS AVIATION...AMS/RAB/WP HYDROLOGY...WP

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