Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 232114 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 414 PM EST Mon Jan 23 2017 .SYNOPSIS...
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A deep low pressure system will drift toward the coast this evening from central North Carolina, triggering periods of rain through the evening. In the wake of the low pressure system, a period of gusty northwest winds are expected for the North Carolina high country and the Blue Ridge overnight into Tuesday morning. Temperatures will rise well above normal for Wednesday, but will trend closer to seasonal levels late in the workweek.
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&& .NEAR TERM /THROUGH TUESDAY/...
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As of 330 PM EST Monday... A deep upper level low pressure system and its associated surface low will continue to drift from central North Carolina toward the coast this evening. Cold air aloft associated with the low is triggering a renewed round of rain showers across the New River Valley and into the foothills this afternoon, a trend that will continue into the mid evening until the better instability associated with the low moves away and winds shift more northwesterly. The first concern for the overnight hours will be an increase in wind speeds around the backside of the departing low pressure system as high pressure approaches from the Mississippi River Valley. Model soundings indicate 50 to 60 mph winds off the surface, which will translate to 45 to 55 mph winds along the higher ridges of the North Carolina Highlands through Floyd County VA. A wind advisory is already in effect for these counties through noon Tuesday. Elsewhere, winds will not be quite as gusty, but may reach 25 mph at times toward sunrise. Also, will be keeping an eye on the possibility of snow showers across the higher ridges on Greenbrier County into the Alleghany Highlands. Outside of those concerns, clouds will gradually decrease from east to west through the night as drier air works into the area on the backside of the departing low. Clearing will continue through the day on Tuesday as high pressure continues to work in from the west. Temperature forecast remains somewhat challenging, moreso for the mountains, as it will depend on the timing of clearing taking place. Have portions of southeast West Virginia and far western Virginia warming into the mid 40s during the afternoon, but admit this may be a few degrees too optimistic. Further east, more confident of temperatures warming into the mid and upper 50s east of the Blue Ridge, where clearing early in the day will allow for abundant sunshine.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
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As of 330 PM EST Monday... Mid-level heights begin to rise significantly Tuesday night into Wednesday, with leftover shallow moisture in the favored upslope region in southeast West Virginia thinning out even further. Forecast trends dry early Tuesday, lasting into a good part of Wednesday as aforementioned mid-level ridge crests over the region. Under plentiful sunshine and 850 mb temperatures between +9 and +11C, Wednesday`s highs stand to be well above normal. Highs into the 60s should be common across the forecast area, and a few point locations east of the Blue Ridge may touch 70 degrees given adiabatic downslope warming off the Blue Ridge. Later Wednesday and into Wednesday night, we start to see modest mid- level height falls associated with a broad, positively-tilted trough with an associated surface front. Front itself moves across the forecast area Wednesday into a part of Thursday. There are some differences between the 12z global suite of models on the degree of precipitation associated with the front, with the GFS and Canadian GEM offering a slightly wetter forecast than the ECMWF depiction. Given that there may be little moisture ahead of the front to work with, sheared-out vort energy and limited progged surface convergence, I`ve kept PoPs on the lower side - no higher than low Chance - closer to the ECMWF idea. Strong cold advection behind the front Thursday, modest post-frontal pressure rises and a northwesterly jet of up to 45 kts will pose at least some risk for at least breezy northwest winds, especially at elevations above 3000 feet. Cold advection aloft also forces northwesterly upslope precipitation in southeast West Virginia, the Mountain Empire and Grayson Highlands down into the North Carolina high country to change from rain to light wet snow by late in the day Thursday. Would expect little if any snow accumulation initially given the prolonged stretch of mild temperatures we`ve had. While still appears to be above-normal from a high temperature perspective - 40s to low 50s - our 850 mb temperatures then start a downward trend late in the day.
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&& .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
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As of 330 PM EST Monday... Our 500 mb height pattern begins to change in the mean to one of cyclonic flow aloft late in the week through early next week. Such a pattern lends itself to relatively unsettled weather conditions and cooler temperatures - to values near or slightly below late-January normals. Indications from today`s global models continue to point to a rather long duration northwest flow upslope snowfall starting Thursday evening into the weekend, and strictly limited to the favored western-facing hillsides in southeastern West Virginia, far southwest Virginia and the high country of North Carolina. It does appear that some light accumulations of snow would be possible through much of this period. How much snow still remains in some question as periods of more persistent snow would be governed to some extent by embedded shortwaves in the broader cyclonic flow, and largely westerly continental flow would also serve to keep available moisture limited. Outside of these upslope areas however, at this point it appears to be a largely cooler and dry period with highs generally in the 30s to low 40s and lows in the 20s.
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&& .AVIATION /21Z MONDAY THROUGH SATURDAY/... 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. && .RNK WATCHES/WARNINGS/ADVISORIES...
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VA...Wind Advisory until noon EST Tuesday for VAZ015>017. NC...Wind Advisory until noon EST Tuesday for NCZ001-002-018. WV...None.
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&& $$ SYNOPSIS...NF NEAR TERM...NF/PM SHORT TERM...AL LONG TERM...AL AVIATION...NF/RAB

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