Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 231114 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 614 AM EST Mon Jan 23 2017 .SYNOPSIS... A strong area of low pressure over the Mid Mississippi valley will approach from the west tonight bringing a period of moderate to heavy rain. This low pressure system will slide slowly east across across the area Monday before exiting Monday night. In the wake of the low pressure system, a period of gusty northwest winds are possible for the North Carolina high country and the Blue Ridge. Temperatures trend closer to seasonal levels by later in the week. && .NEAR TERM /THROUGH TONIGHT/...
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As of 530 AM EST Monday... Regional surface analysis depicts strong low pressure of 986 mb over southwestern NC with the upper low over North Georgia. System is nearly vertically stacked with main area of lift and associated rainfall spiraling around the northern periphery of the surface low. Surface cyclone is progged to move east to along the North Carolina Coast by this evening, then northeast to near the Delaware coast by daybreak Tuesday. For Today: Moderate to locally heavy showers will continue this morning with embedded thunderstorms over southside VA into the NC piedmont. Rainfall of 1 to 2 inches will be common. As long as the showers remain transient, then amounts should remain at or below 2 inches. Some concern exists for potential flooding, but since individual convective cells are moving so fast, residence time of the heaviest rain will be limited. Worse case would be for training to occur. Unless we start to see rainfall amounts exceed 2 inches, will forgo Flood Watch and/or warnings attm. Models are in relative agreement the overall area of rain will lift north as a dry slot works around the east side of the upper low. This should cause the rain to become more showery east of the Blue Ridge as that process proceeds. North and west of the dry slot the rain will remain more continuous. A strong East-Northeast fetch of wind is being drawn into the low from the coastal Atlantic. This is resulting in some healthy wind gusts from southside Va northeast along the eastern slope of the Blue Ridge. Models suggest this wind will continue through at least noon before veering and decreasing as the low passes by just to our south this afternoon. Once the low gets to the coast, then concern for stronger wind speeds will focus on on the NC high country and the Blue Ridge southwest of Roanoke where models suggest speeds of up to 50 mph are possible late tonight into Tuesday morning. For Tonight: The rain threat will subside, becoming more confined to the west, upslope side of the Appalachians. With lingering precip in the mountains there may be some mix of snow at the higher elevations north of Bluefield and west of Lewisburg where temperatures slip into the lower to mid 30s. The NAM is by far the coldest of the models suggesting an inch or two for western Greenbrier. Attm think this is overdone and will go with the slightly warmer GFS which indicates only a coating to an inch. Elsewhere, the boundary layer appears to be too warm, so will keep the p-type as rain. On the downslope, east side of the Appalachians look for partial clearing.
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&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
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As of 400 AM EST Monday... Upper low near the VA/DE coast Tuesday, will head northeast out to sea on Wednesday. Cooler air will follow this system Tuesday, however high temperatures will remain above normal. Also in the wake of this system, pressure gradient and rises, subsidence and a 40-50kt low level jet will bring windy and gusty conditions to the area. These strong winds will start across the southern Appalachian Mountains in North Carolina Monday night into Tuesday morning, then across southwestern Virginia early Tuesday morning into Tuesday evening. Winds will be their strongest across northwestern North Carolina, enough to issue an advisory. High pressure and upper level ridging will move over the region Tuesday night, ending the threat for strong winds. A disturbance will track east across the Great Lakes Wednesday. The cold front associated with this disturbance will not cross the area until Wednesday night. With abundant sunshine and increasing southwesterly flow ahead of the front, temperatures will warm 20F above normal Wednesday with widespread 60s across the forecast area to near 70F across Southside Virginia.
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&& .LONG TERM /THURSDAY THROUGH SUNDAY/... As of 337 PM EST Sunday... Pattern change to overall broad longwave troughing over the region will begin to take shape Thursday in the wake of a passing surface cold front by early in the day. This will lead to a prolonged period of cold advection under west/northwest flow to the east of the main surface high situated over the Rockies through next weekend. However appears the overall scenario to remain on the quiet side with mainly shallow moisture resulting in upslope driven periodic snow showers espcly northwest sections into Sunday. Appears amounts to be limited though given more westerly trajectory and only shallow moisture beneath the inversion, so overall only chance pops this far out along the western slopes. Otherwise should see the typical split from mainly sunny/clear skies east of the ridges per downslope, to clouds far west, and at times out to the Blue Ridge pending the passage of weak impulses. With the broad trough becoming rather flat and 850 mb temps roughly above minus 10C, only expecting a return to normal or slightly below normal temps with highs 30s/low 40s mountains, to low/mid 40s east, and lows in the 20s. However will feel quite a bit colder after all the recent warmth, given a persistent blustery northwest wind under the lingering gradient between low pressure well north and the high well to the west. Appears coldest could occur during the weekend when thickness drop a bit so trended toward the colder earlier EC mos as the GFS MEX values remain warmer. && .AVIATION /10Z MONDAY THROUGH FRIDAY/...
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As of 600 AM EST Monday... Poor flying conditions will continue across much of the region and at all TAF sites through early afternoon. Wedge/CAD conditions in place with widespread IFR-LIFR ceilings and MVFR visibilities with intermittent periods of IFR rain. Some lightning has been detected in the showers east of the Blue Ridge. Deep upper low across the southeast states is moving northeast today, reaching the NC coast by this evening before inching its way up the coast and just offshore tonight and Tuesday. Rain and low cigs will be common throughout the region today with a gradual improvement later this afternoon and tonight, and an eventual return to VFR Tuesday on the east side of the Appalachians. Wrap around moisture from the storm will likely result in persistent low cloudiness in the mountains through Tuesday, although these cloud bases should improve with time. There is a strong East-Northeast barrier jet along the east side of the Appalachians this morning. This is resulting is wind gusts of 30 kts vcnty of LYH and CHO this morning. This jet is expected to weaken by early afternoon. Additional wind concerns will develop in the wake of the departing storm tonight and Tuesday with strong northwest winds developing across the ridges after midnight with the potential for 30-40 kt gusts. Extended Aviation Discussion... Winds will subside Tuesday night. High pressure will finally spread into the region by Wednesday. A band of MVFR showers is possible along/behind a cold front Thursday into Thursday night. Colder west to northwest wind flow will develop behind this front with mountain snow showers possible for the weekend associated with MVFR CIGS/VSBYS.
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&& .HYDROLOGY...
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As of 600 AM EST Monday... Periods of rain will continue to impact the Blacksburg hydrologic service area today, heaviest this morning. Rainfall amounts of 1 to 2 inches will likely result in rising stream levels. While minor to moderate rises on rivers, streams, and creeks can be expected, flooding is not anticipated at this time. Only if rainfall begins to exceed 2 inches would flooding become a concern. Although this is locally possible, the risk for widespread flooding is low enough to forgo need for an areal flood watch. Of more concern will be ponding of water on roads and reduction in visibility due to the intermittent heavier showers.
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&& .RNK WATCHES/WARNINGS/ADVISORIES...
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VA...Wind Advisory from 6 PM this evening to noon EST Tuesday for VAZ015>017. NC...Wind Advisory from 6 PM this evening to noon EST Tuesday for NCZ001-002-018. WV...None.
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&& $$ SYNOPSIS...PM NEAR TERM...AL/PM SHORT TERM...RCS LONG TERM...JH AVIATION...AL/KK/RAB HYDROLOGY...AL/PM

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