Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 231835 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 135 PM 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/... As of 1130 AM EST Monday... Radar imagery indicates that the heaviest rain has exited the area to the north northwest as the upper low and nearly vertically stacked surface low make a jog from central North Carolina to the coast. Currently, only areas of light rain continue to pass across the forecast area. One of the chief concerns through at least mid afternoon will be rapid rises along creeks and smaller rivers in the vicinity of the Blue Ridge, especially in the Roanoke area. Runoff from the heavier rainfall earlier will continue to push these rivers higher through early afternoon, in some cases out of their banks to result in minor flooding. With no organized additional heavy rain expected today, expect that most rivers and creeks will crest during early afternoon, and will begin to recede before the afternoon commute. The pressure gradient east of the Blue Ridge remain tight enough to support 25mph to 35mph gusts as of 11 AM...longer than what weather forecast models have anticipated. Will update the forecast to reflect stronger gusts through mid afternoon, by which time winds speeds are expected to diminish as the low pressure system continues east. Also, with clouds expected to hold in place through the day, expect that we are already within a degree or two of or daytime high temperatures, and will adjust the forecast accordingly. For Tonight: The rain threat will continue to 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. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... 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. && .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 /18Z MONDAY THROUGH SATURDAY/...
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As of 100 PM EST Monday... Poor flying conditions will continue across much of the region and at all TAF sites through early Tuesday morning. Stacked upper level/surface low pressure systems currently making their way eastward across central North Carolina. As the lows progress, winds continue to back increasingly north- northeasterly. IFR ceilings remain widespread, with visibilities ranging from IFR to VFR depending on locality and proximity to rain showers developing under the upper low. Do not expect much change in these conditions through 24/06Z, by which time winds will back more northwesterly as low begins to push away. With the northwest wind shift overnight, expect cloud cover to decrease from east to west due to downslope flow. Believe that LYH/DAN/ROA will have scattered to VFR ceilings before 24/12Z while BCB will linger in low clouds through early Tuesday afternoon. Do not expect BLF/LWB to break out of MRVF/IFR until late Tuesday. Eastward push of the low pressure system will also cause wind speeds to increase as the pressure gradient tightens between the departing low and high pressure along the Mississippi River Valley. Expect 20kt to 30kt northwesterly surface gusts to be common areawide beginning Tuesday morning, with as high as 35kt possible at ROA due to wind channeling in the local terrain. 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... As of 1130 AM EST Monday... Heavy rainfall has exited the area, with only light pockets of rainfall expected to remain through the day. Area creeks and streams will continue to rise through early afternoon, with some pushing out of their banks in spots for a few hours. Expect all rivers to begin receding by mid afternoon. && .RNK WATCHES/WARNINGS/ADVISORIES... 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. && $$ SYNOPSIS...PM NEAR TERM...AL/NF/PM SHORT TERM...RCS LONG TERM...JH AVIATION...NF/RAB HYDROLOGY...AL/PM

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