Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 151742 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1242 PM EST Wed Feb 15 2017 .SYNOPSIS... Low pressure over the Tennessee valley will cross the southern Appalachians this morning, then move east to along the North Carolina Coast this afternoon. Meanwhile, a cold front over the Great Lakes and Ohio Valley will move east, also crossing the Appalachians this morning, then to along the Mid-Atlantic coast this afternoon. The area of low pressure is then forecast to move northeast along the front tonight, strengthening into a winter storm as it passes near the New England coast. && .NEAR TERM /THROUGH THURSDAY/... As of 1013 AM EST Tuesday...Update to remove the Winter Weather Advisory for Tazewell County as snowfall has shifted well eastward and accumulating snowfall from earlier this morning having shifted well to the east. Generally nowcasted PoPs/Wx across the eastern part of our forecast area through 17z. Higher-resolution guidance is running about 2 hrs slower than the band of ongoing light rain across Caswell NC and Halifax/Charlotte counties in VA is moving; but used a blend of it into the updated forecast to reduce PoPs in these areas. Cold front aloft - essentially manifesting itself as a fine line of reflectivity extending from central PA southwestward into north-central WV - gradually working its way southeastward. HRRR and WRF ARW/NMM depict at least some potential enhancement into southeastern WV again into the early afternoon. So I`ve generally maintained isolated snow/rain showers into the afternoon for these areas. Otherwise, made no other changes to the forecast at this point. Expect some breaks in overcast through the early afternoon with temps only slowly climbing west of the Blue Ridge, with a bit more of a diurnal trend out east. Previous near-term discussion issued at 500 AM follows... Vigorous short wave trough over the eastern TN valley will move east this morning crossing the southern Appalachians. Area of precipitation cover the central and southern Appalachians with primarily rain in the lower elevations, and some snow in the higher elevations. Within our CWA, the snow has been confined mainly to the western New River Valley and into the high country of NC and the mountains of far southwestern VA, including Mercer County WV. Do not have a lot of ground truth to offer, but there has been a mesoscale band of moderate snow aligned from west to east across Tazewell County Virginia since midnight, so would anticipate upwards of 2 to 4 inches of snow between Bluefield and Marion...especially across the higher terrain... such as East River Mountain, Rich and Brushy mountains, and along Big Walker mountain near Bland. Models indicate moisture associated with the area of low pressure will peak early this morning between now and 9AM, then taper from west to east across the CWA between 9AM-Noon...exiting the CWA for this afternoon. The eastern part of the New River Valley, and higher terrain near the Blue Ridge may see a mix or change over to snow before the precipitation comes to an end. Ground temperatures are warm, so not expecting any road issues, other than just being wet. For this afternoon, the short wave and associated surface low will pass off the NC coast, and will begin to phase with an upper level long wave trough which is moving east across the Great Lakes. This phasing will result in a rapid strengthening of the surface low (initially at 1000 mb), the pressure dropping to near 975 mb as the storm moves northeast along the New England Coast tonight. End result will be a winter storm with heavy snow for parts of New England, and strong Northwest winds across the Mid-Atlantic with near advisory level gusts across the mountain ridges. In addition to the wind, wrap around moisture from the storm will combine with low level moisture from the Ohio Valley side of the mountains to produce snow showers and flurries across the VA/WV highlands with some accumulating snow north and west of Lewisburg. Temperatures today will warm very little until we begin to clear this afternoon. Introduction of a little sun, will allow temperatures to sneak above freezing in the mountains and into the 40s to near 50 for the foothills and piedmont. 85H temperatures take a respectable plunge tonight (M8 to M10 deg C by 12Z/7AM Thursday), so all areas expected to drop below freezing tonight, with readings in the teens for elevations above 3500 feet MSL and wind chill readings in the single digits for Thursday morning for areas west of the Blue Ridge. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/... As of 400 AM EST Wednesday... Northern stream and southern stream systems will be phased together along the eastern seaboard at the beginning of this period resulting in a deep upper trough anchored just east of the Appalachian Divide and centered over New England. Lingering upslope snow showers will be possible through the first half of the day with low-level cold advection in place. Expect a fairly decent surge of cold air to be in place as 850mb temps plunge back toward the -12C level. The ECMWF has trended a tad colder with this air mass while the GFS has trended a tad warmer, but both are in the -10C to -12C range across the northern parts of the CWA. This will yield lows in the upper teens across the higher elevations of the western mountains to the mid and upper 20s across the Piedmont. Gusty northwest winds will be the main concern for Thursday until the upper trough begins to lift out during the afternoon. Winds may well approach wind advisory criteria across northwest NC into southwest VA, especially along the higher terrain of the Blue Ridge. For now, will just highlight the mention of such in the HWO and allow the day shift to take a closer look at this before issuing an advisory. The upper trough will begin to lift out fairly quickly during the afternoon and evening allowing low-level warm advection to ensue sooner than with previous similar such cold fronts/air masses. This will allow afternoon maximum temperatures to recover to the 30s west to the 50s east, roughly just a bit below normal. Weak northwest flow aloft will prevail for Friday as the upper trough lifts further northeast away from the region. The northern stream will gradually lift north Friday through Saturday with the southern stream remaining quite active along the southern border of the U.S. A powerful storm system will shift eastward into the southwestern U.S. with pieces of energy ejecting eastward from this system along the Gulf Coast states. Meanwhile, a mean ridge will dominate the east central U.S. during this period. 850mb temps will rise dramatically toward +10C by the end of the day resulting in a rapid warmup from the cold weather of Thursday. Maximum temps Friday will be a good 10-15 degrees warmer than Thursday, namely 50s west to 60s east. The first southern stream system of concern for our area will lift northeast from the southeast states in a greatly weakened fashion. Despite the weakness of this system and generally lifting into an area of confluent flow, the models have gradually been increasing the impacts of this system on our region resulting in a period of light rain likely spreading into the area Saturday night into Sunday morning. With temperatures well above freezing, there are no concerns for any winter precipitation with this event. Increased cloud cover Saturday will hold max temperatures into the 50s west and 60s again east, but this is still well above normal for mid-February. && .LONG TERM /SUNDAY THROUGH TUESDAY/... As of 445 AM EST Wednesday... The deep upper low along the west coast will slowly shift eastward through the far southwestern U.S. into Texas and the western Gulf Coast states during the first half of next week. Meanwhile, an upper ridge in advance of this upper low will drift slowly east into the eastern U.S. Beyond Monday, significant timing and track differences are noted between the various long range models, with the ECMWF faster and further south with the upper low, while the Canadian and GFS remain further north and much deeper/more intense. The ECMWF solution would take the track of the upper low so far to the south that the Mid-Atlantic region/central Appalachians would only be left with some light showers in a lingering confluent zone. The GFS, on the other hand, would bring a substantial amount of rainfall and possibly even some stronger convection into our area late in the week. At any rate, it will be mid week or later before any model brings sensible weather from this system into our region. Thus, mostly dry and unseasonably warm weather will prevail until that time. With 850mb temps hovering in the +10C to +12C range throughout this period, look for surface lows in the 40s and 50s and highs in the 60s and 70s. These temperatures are a good 15-20 degrees above normal. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
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As of 1241 PM EST Wednesday... Generally SCT-OVC VFR stratocu through 00z as a dry cold front advances southeastward, with a wind shift to northwest 10-12 kts gusts to 25 kts accompanying the frontal passage. While skies clear early this evening for most of the TAFs, expect a lowering to MVFR around/after 02z as moisture from the Great Lakes is forced upslope, predominantly affecting BLF and LWB. These ceiling trends generally continue until around mid-day Thursday. Gusty northwest winds will continue through the remainder of the TAF period, gusting the strongest at BLF and ROA (30-32 kts). Given the strong wind field, some potential for turbulence in/around the ridgetops due to mountain waves Thursday. Extended Aviation Discussion... Ceilings begin to improve to VFR all terminals late Thursday afternoon. While winds will continue to be rather gusty, anticipate a diminishing trend to northwesterly sustained wind and gusts during the overnight hours on Thursday. Generally VFR overnight into early Friday, perhaps briefly falling to an MVFR ceiling at BLF and LWB as a shortwave trough rotates southeastward. Next potential for sub-VFR conditions is not until later Saturday as a disturbance moves in from the Deep South producing showers. Lower ceilings may linger into Sunday across BLF and LWB, but becomes VFR Sunday night through Monday.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PM NEAR TERM...AL/PM SHORT TERM...RAB LONG TERM...RAB AVIATION...AL/PM is the U.S. government's official web portal to all federal, state and local government web resources and services.