Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 211140 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 740 AM EDT SAT MAY 21 2016 .SYNOPSIS... Low pressure off the North Carolina coast will deepen and move northeast today through Sunday as a weaker low over the Ohio Valley tracks southeast and dissipates. High pressure over the central United States will move east Monday and Tuesday, then off the East Coast on Wednesday. && .NEAR TERM /THROUGH TONIGHT/... As of 430 AM EDT Saturday... Water vapor loop showed short waves crossing through the Ohio Valley and Mid Atlantic region early this morning with the upper low over Indiana. Main band of moderate rain was over the eastern half of the county warning and was progressing east. High Res WRF guidance along with HRRR and local WRF all have the western edge of the rain just exiting the forecast area around 12Z/8AM. MSAS analysis showed increasing pressure falls over eastern Virginia and North Carolina. The coastal low will move northeast and continue to deepen today with northwest winds in the eastern county warning area around this system. The low in the Ohio Valley will drift southeast today with winds over the mountains from the southwest. By the end of the day the coastal low will be deep enough to turn the winds across the forecast area to the northwest. Deeper moisture returns as the upper low approaches the area this afternoon, after brief drying in mid levels this morning. Bufkit forecast soundings showed large lapse rates this afternoon and short term guidance had scattered showers develop as early as 16Z/noon over the mountains. As winds come around to the northwest and the wedge breaks, there will be enough breaks in the clouds for some heating, especially in the North Carolina foothills, which will aide in destabilizing the air mass this afternoon. Have isolated to scattered thunder where the wedge retreats today. More questionable in the extreme northeast county warning area when and if the more stable air and low clouds will erode. Much of the guidance keeps Amherst, Appomattox and Buckingham counties in the cooler air through most of the day. Where there are breaks in the clouds today, temperatures will have a decent chance of getting into the lower 70s. Where the stable air remains in place, highs may only be in the lower to middle 60s. Any thunderstorms and some of the showers will dissipate with loss of heating this evening. Have held onto a chance of showers mainly in the northwest and eastern county warning area. Lows will be near normal. && .SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/... As of 330 AM EDT Saturday... The persistent blocky pattern will keep a closed low spinning off the mid Atlantic coast into the first part of next week. Cold temperatures aloft will create steep lapse rates and combine with diurnally driven instability along with short wave impulses to bring a good chance of showers and some thunder to our forecast on sunday. The low will still be close enough to us on Monday to keep some showers/thunder in the forecast mainly east of the Blue Ridge but by Tuesday we can expect some low amplitude ridging aloft to move in as the surface low moves up the coast towards Cape Cod. This should finally allow us to dry out a bit as we head towards midweek. Temperatures will start the period well below normal with highs on Sunday only in the low/mid 60s west of the Blue Ridge and in the upper 60s/near 70 to the east. But by Tuesday as the closed low loses its influence over our weather and temperatures moderate we will see readings return to normal levels with low/mid 70s west and upper 70s/around 80 east. && .LONG TERM /WEDNESDAY THROUGH FRIDAY/... As of 330 AM EDT Saturday... Broad low amplitude ridging will continue our moderating trend with temperatures well above normal Wednesday through Friday. However with the warmer temperatures will come moisture and a better chance for showers and thunderstorms each afternoon and evening...especially from the Blue Ridge westward. The pattern does not favor organized convection so any storms are expected to be of the pulse variety. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
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As of 740 AM EDT Saturday... Area radar indicated moderate rain was east of KLYH and KDAN as of 11Z/7AM. Isolated light showers were over the mountains. Low pressure off the North Carolina coast will continue to deepen and move northeast today. This will help erode the wedge east of the Appalachians as surface and low level winds come around to the northwest. As the upper low and associated cold pool aloft move southeast out of the Ohio Valley today, scattered showers and isolated thunderstorms will develop outside of the wedge. Large lapse rates will add to instability this afternoon as seen on the NAM and GFS Bufkit forecast soundings. Medium confidence on the areal coverage of any thunderstorms this afternoon. For now have left any thunder out of the TAFs. Expecting IFR to MVFR clouds to fill back in after sunset. Locations that have rain this afternoon may have MVFR to IFR fog overnight. High confidence in the evolution of events today, but low confidence on the timing. KLYH may stay in the wedge and stable air well into the afternoon. Extended discussion... Sunday and Sunday night, cigs look to remain quite variable under the passing upper low with periods of mainly MVFR cloud bases during the daylight hours and VFR cigs at night. Isolated to scattered showers will also occur, espcly across the east Sunday into Sunday evening making for MVFR vsbys or worse at times. Isolated thunder will also be possible along with patchy sub-VFR vsbys overnight in fog where earlier rainfall occurred. Northwest upslope flow may maintain some IFR ceilings at times in the west espcly around KBLF. Surface gusts of 20 to 25 kts will be possible across the mountains Sunday and Sunday night. 850 mb winds are progged to increase to 25 to 35 kts, and gradually veer northwest to north. On Monday, winds will start to decrease as the center of the upper low continues to exit the region. Isolated showers will still be possible, especially in the east, related to this feature. Monday night through Wednesday, expect mainly VFR conditions as high pressure settles offshore with southwest flow in place.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AMS NEAR TERM...AMS SHORT TERM...MBS LONG TERM...MBS AVIATION...AMS/JH

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