Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 201134 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 734 AM EDT FRI MAY 20 2016 .SYNOPSIS... Low pressure over the lower Mississippi Valley will deepen and move northeast into the Tennessee Valley today and tonight. At the same time, another low develops off of South Carolina and tracks northeast along the coast. By Sunday, these systems transition to a strong low well off of the New Jersey coast. && .NEAR TERM /THROUGH TONIGHT/... As of 430 AM EDT Friday... Low pressure will develop over the Tennessee Valley today. This will enhance a wedge of high pressure over the forecast area as a second low forms off the Carolina coast. Models were in good agreement spread clouds northeast across the region followed by rain. Have slowed the onset of the rain in the northern and eastern county warning area until late afternoon. Best forcing and isentropic list as well as strong upslope will be from 00Z/8PM through 06Z/2AM. 850MB southeast low level jet increases to around 40KTS which will enhance the upslope and precipitation amounts on the eastern slopes of the Blue Ridge. Have raised wind speeds and gusts in the western downslope area overnight. Expect the smallest rise in temperatures in the southwest county warning area, especially once the rain begins. Took a blend of guidance for lows tonight. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 330 am Friday... A Miller B type system expected with parent low weakening over the Ohio Valley and the energy is transferred to the coastal low. The upper level trough will move out of the Great Lakes and push the moderate to heavy rain east of the area Saturday. The challenge in the forecast is how long does it rain hard before the secondary low becomes the primary low Saturday afternoon, pulling bulk of the precipitation out to sea. Several shortwaves will rotate around the upper trough generating scattered convection afternoon into Saturday evening. High temperatures Saturday will range from the upper 50s in the northern mountains to the lower 70s in the Piedmont. We may see warmer than expected temperatures Saturday depending on when the bulk of the rain exits. The Coastal surface low lifts northeast along the coast Saturday night. The upper level trough will pivot over the region Saturday night, keeping the chance for rain showers especially over the mountains. A few showers may overcome northwest flow and push east of the Blue Ridge overnight. Low temperatures Saturday night will drop into the mid 40s in the mountains to the mid 50s in the Piedmont. Cold pool remains over the region Sunday and with afternoon heating, scattered showers and isolated thunderstorms are possible into the evening. Sunday afternoon high temperatures will remain below normal with readings from lower 60s in the west to the lower 70s in the east. The upper trough becomes a closed low Sunday night off the Mid Atlantic coast. As the low moves away, the chance of rain will decrease with our area in a subsidence region. The locations of this feature is similar on both the ECMWF and GFS. Low temperatures on Sunday night into Monday morning will generally be from the mid 40s in the west to the lower 50s in the east. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 330 AM EDT Friday... 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 decrease 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 /12Z FRIDAY THROUGH TUESDAY/...
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As of 730 AM EDT Friday... Leading northern edge of 4000-6000FT ceilings was advancing north across Virginia and will cover KLWB and KLYH just after the 12Z start of the TAF forecast period. Patchy dense fog with LIFR visibility had developed overnight. Visibility will improve this morning as mixing begin but only meduim confidence on the timing of this improvement. Ceilings will gradually lower today as a low pressure system approaches from the southwest. Models, including the GFS and variations of the WRF showed good consistency with the timing of the MVFR ceilings and arrival time of light to moderate rain. Still high confidence there will be widespread moderate to heavy rain across the region ceilings lowering to IFR between 00Z and 06Z. A low level jet from the southeast tonight will produce some wind gusts of 25 to 35 knots along the ridges. Gusts up to 30 knots are possible at KBLF. 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 be VFR.
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&& .HYDROLOGY... As of 450 AM EDT Friday... Consistent forecast from the models and the Weather Prediction Center with one to two inches of rain expected across the forecast area from this afternoon through late in the day Saturday. A bulk of this precipitation will fall this evening into Saturday morning. There is still a potential that this longer duration rainfall will lead to localized minor flooding along streams and creeks. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AMS NEAR TERM...AMS SHORT TERM...KK LONG TERM...KK AVIATION...AMS HYDROLOGY...AMS

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