Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 192327 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 727 PM EDT THU MAY 19 2016 .SYNOPSIS... High pressure will be over the region tonight into Friday. Low pressure will advance towards the region Friday and move through the area Friday night into Saturday. An upper trough of low pressure will progress across the area on Sunday with area of high pressure close behind it for Monday. && .NEAR TERM /THROUGH FRIDAY NIGHT/... As of 335 pm EDT Thursday... High pressure was making its way into the region. Throughout the day, patchy light rain and drizzle has been slowly exiting the region to the south. Likewise, drier air has been eroding some of the cloud cover across the northern third of the forecast region. Cloud cover has held fast nearest the NC/VA border. Through the overnight hours, anticipate the lee side wedge to gradually become more entrenched. Anti-cyclonic flow around the wedge, plus the influence of an approaching area of low pressure, will bring wind around to the southeast across much of the region. The resultant flow will allow for cloud covers to redevelop where they had cleared earlier today. Areas with clouds currently, will remain cloudy. Also, patchy light rain will start to work its way back into the southwest portion of the area and spread slowly northeast. Light fog development is also anticipated for much of the region. Lows tonight will range from the mid 40s to around 50 across the mountains with upper 40s to lower 50s across the piedmont. Friday into Friday night we are still expecting widespread rain to overspread the region from southwest to northeast. Plenty of Gulf of Mexico moisture will be advected into the region in advance of an approaching area of low pressure. Moderate to heavy rain is still very likely late Friday afternoon through Friday night. At this time however, the amount of forecast rainfall does not warrant a flash flood or flood watch. Please reference the HYDROLOGY section of this discussion for more details. We will continue to discuss the expected moderate to heavy rain in the Hazardous Weather Outlook. High temperatures on Friday will range from the upper 50s to lower 60s across the mountains to the lower 60s to upper 60s across the piedmont. Lows Friday night will be a mix of the lower 50s across the mountains to the mid 50s across the piedmont. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 330 pm Thursday... An upper level trough will swing out of the Great Lakes and kick the heavy rain east of the area Saturday. The parent surface low is over the Ohio Valley with a secondary low forming off the Virginia coast. This may delay the exit of moderate to heavy rain Saturday morning, therefore left high PoPs. The secondary low becomes the primary low Saturday afternoon, pulling bulk of the precipitation out to sea. However, that does not end our rain chances. The upper level trough coming across the Ohio Valley will pivot over the region Saturday night, keeping the chance for rain showers over the mountains. A few showers may overcome northwest flow and push east of the Blue Ridge overnight. Cold pool remains over the region Sunday and with afternoon heating, scattered showers and isolated thunderstorms are possible into the evening. This trough is expected to become a closed low Sunday night. If this low is off the Mid Atlantic coast, then the forecast area will be in a subsidence region keeping our chance for showers low. If the low remains closer to the shore or inland, showers chances will remain Sunday night into Monday. We may see warmer than expected temperatures Saturday depending on when the bulk of the rain exits. Cooler air is not expected to enter the area until the trough pivots east. For now, temperatures will remain below normal and in the lower to mid 60s. Some areas across northern North Carolina may make it to 70F late Saturday. Sunday may be a little warmer with more chances to see the sun. Sunday afternoon will remain below normal with highs in the mid to upper 60s west to lower 70s east. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 330 pm Thursday... An upper level low in the vicinity of the Mid Atlantic will keep a chance for showers and a few afternoon thunderstorms in the area Monday. If this low wobbles offshore, the area will be in the subsidence zone and with high pressure building east, the chance for rain will drop to zero for a few days. Once this low departs, upper level ridging will increase, which means warmer temperatures are on the way. However, with warmer temperatures, the threat for thunderstorms will increase which looks to begin Wednesday. The threat of convection may hang around through the end of the week. Temperatures will moderate to near normal on Monday, then above normal for the remainder of the workweek. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/...
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As of 720 pm EDT Thursday... Overnight, low level moisture will condense into IFR/MVFR ceilings with some light fog possible as well in spots under a developing wedge of high pressure. After about 14Z/10am Friday, flight categories will again improve to VFR as the nocturnal inversion breaks. Rain will again start progressing into the area by the late morning across southwest portions of the forecast area. At this time, none of the TAF locations are expected to be impacted by 21Z/5pm. Rain will overrun the region Friday afternoon into Friday night on the east side of an approaching upper level trough and surface low. This rain will help to strengthen the lee side wedge. Anticipate cloud cover to trend to IFR/MVFR ceilings with MVFR visibilities for rain and light fog. Extended discussion... Saturday, the precipitation will trend more showery as the axis of the upper trough draws close and the surface low passes overhead. Flight conditions will improve as the low level winds become northwest and the lee side wedge erodes. Isolated afternoon thunderstorms cannot be ruled out as surface instability increases, especially in the west. Sunday, mainly VFR conditions are expected along with some hit or miss showers as the axis of the upper trough passes across the region. The best potential for MVFR conditions will be across southeast West Virginia where northwest upslope cloud cover is expected. Monday into Tuesday, most areas will experience VFR conditions as an upper level shortwave ridge noses itself into the area.
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&& .HYDROLOGY... As of 335 pm EDT Thursday... The latest WPC quantitative precipitation forecast for the time period of Friday through Saturday places an average of 1.25 to 2.00 inches across our region, with 75 to 85 percent of that occurring Friday night. The latest flash flood guidance from the river forecast center offer anywhere between 1.50 to 4.00 inches of rain in six hours to prompt flash flooding with similar values forecast to be required to prompt flash flooding in three hours. Our largest forecast six hour precipitation forecast Friday night is on the order of 0.80 to 0.90 inches in six hours. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...DS NEAR TERM...DS SHORT TERM...RCS LONG TERM...RCS AVIATION...DS/RCS HYDROLOGY...DS

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