Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 240447 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1147 PM EST Mon Jan 23 2017 .SYNOPSIS... A deep low pressure system will continue to shift to the mid- Atlantic Coast tonight. 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. && .NEAR TERM /THROUGH TUESDAY/... As of 920 PM EST Monday... While radar trends have diminished over the course of the evening there is still narrow bands of precipitation lined up north to south from Southeast WV to the NC piedmont. Models having a difficult time showing this in the near term and have been pulling the main precip threat to the southwest VA mountains overnight. This in line with upper pattern as sharp vort max rotates southeast to the Southern and Central Appalachians overnight. Temperatures sub-freezing in higher elevations will lead to some snowfall, possibly freezing drizzle or freezing rain if depth of moisture falls below the ice crystal formation zone. The threat of a good snow is nil, but some locations such as Mt Rogers, and Quinwood, WV are in line to get about an inch of snow. Though temperature at the higher elevations will be at or below freezing, a wet and warm ground should prevent most roads from becoming slick, so not expecting any hazards as far as snow goes. As far as winds goes, still looks likely the low level jet around 50 kts moves across the NC mountains between 06-12z and with some decent pressure rises, as well as lowering inversion should see some gusts close to 50 mph, in locations such as Boone and West Jefferson. Also with wet soils, some weakly rooted trees are likely to fall, so do not be surprised if some power outages occur across the High Country and northward toward Meadows of Dan late tonight into Tuesday morning. No other major changes were needed with lows still mainly ranging from upper 20s to lower 30s in the higher elevations to lower 40s southeast. Previous valid discussion... 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. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... 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. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... 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. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/...
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As of 1142 PM EST Monday... Narrow ribbon of upper energy and lift keeping a band of showers across southeast WV into the NC foothills, or roughly along a LWB-INT track as of 0440z. Expect the focus of showers to shift west overnight with diminishing trend at LWB/ROA. Will maintain a tempo group at BCB for moderate showers and MVFR vsbys. Overall still looks like flow will turn more northwest early in the period and lead to VFR conditions east of the mountains. As we head toward dawn winds will pick up a bit especially from Roanoke/Blacksburg and west with some gusts to 30 kts possible. Will see showers confined to BLF for most of the night then taper after 11z. Cloud cover will also lift to VFR at all sites between 10-16z except BLF which should hang onto MVFR cigs til 00z/25. Winds should start to fall off after sunset Tuesday as well. Extended Aviation Discussion... 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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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...Wind Advisory until noon EST Tuesday for VAZ015>017. NC...Wind Advisory until noon EST Tuesday for NCZ001-002-018. WV...None. && $$ SYNOPSIS...NF/WP NEAR TERM...NF/WP SHORT TERM...AL LONG TERM...AL AVIATION...NF/WP

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