Area Forecast Discussion
Issued by NWS Blacksburg, VA

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011 FXUS61 KRNK 130449 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1149 PM EST Wed Dec 12 2018 .SYNOPSIS... High pressure will remain over the region tonight ahead of a weak cold front that will approach from the west overnight before dissipating across the mountains on Thursday. A developing low pressure system will eject northeast out of the southern states Thursday into Friday before crossing the Mid Atlantic region this weekend. High pressure follows this system for early next week. && .NEAR TERM /THROUGH THURSDAY/... As of 845 PM EST Wednesday... Lower level moisture continues to slide east across the mountains tonight in advance of low pressure passing well to the north, and ahead of a weak surface cold front entering the Ohio Valley. Expect some of this cloudiness to spill east crossing the Blue Ridge overnight before getting clipped by downsloping westerly flow as seen via the evening RNK sounding aloft. Soundings also show quite a bit of dry air in the low levels which so far has acted to keep cloud bases higher, and the northwest sections free of any freezing drizzle per forecast shallow moisture beneath the mid level inversion. Latest Nam/HREF still indicate the potential for some spotty very light precip in southeast West Va overnight, so keeping in mention for spotty freezing drizzle for now. Otherwise beefed up clouds early on west, and kept things mainly cloudy outside of the piedmont where appears skies will stay clear longer. Temps remain quite varied given clouds/mixing mountains and decoupling over snow pack in the valleys near the Blue Ridge and outlying eastern locations. Appears most lows outside of the piedmont to occur through midnight before steadying/rising pending extent of the low clouds through dawn. Thus lowered readings a few degrees where already at earlier forecast lows before slowly rising as clouds arrive mountains, while keeping the east also colder under better radiational cooling a bit longer. Previous discussion as of 242 PM EST Wednesday... High pressure over Georgia and Florida this afternoon will slide east tonight into Thursday. Low pressure centered near Chicago will drop southeast quickly tonight into Thursday. Plenty of high clouds across the region enhanced by standing wave clouds downstream of the southern Appalachians and high level moisture advection into our region. Some low clouds will from in the mountains tonight. Shallow moisture will advect into the western mountains late tonight. Bufkit model sounding support the mention of slight chance of drizzle or freezing drizzle in the northwest mountains late tonight. The NAM and HiResW-ARw-East had some light return in the northwest mountains. Low temperatures tonight will range from the mid 20s along the southern Blue ridge to the lower 30s in the far west mountains. The upper low center will slide from the Great Lakes to southern New England on Thursday with mid to upper ridging building overhead. A cold front will be approaching from the west Thursday. High temperatures will vary from the lower 40s in the northwest to the upper 40s in the southeast. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/... As of 242 PM EST Wednesday... An active weather pattern is forecast to close out the end of the week. High pressure over the northern mid Atlantic will transition into a wedge Thursday night ahead of an approaching low pressure system moving out of the lower Mississippi valley. Wedge of high pressure is expected to keep shallow layer of cold air locked into place within the boundary layer with a chance for some freezing rain as precipitation overspreads the region by daybreak Friday. Confidence in fine details of the temperature forecast and resulting precipitation type is not high, but there is the potential for some locations mainly north of Route 460 to pick up a light glaze of ice early Friday morning before a transition to all rain. As the precipitation advances, the low level wind field will become quite energetic with some gusty winds expected at the higher elevations west of the Blue Ridge, especially from the NC mountains up into the Mountain Empire region of VA, and from Bluefield to Beckley in WV. Per the 12Z model guidance primary focus for the heaviest rain from this system will be late Friday into Saturday. QPF of 1 to 2 inches of rain seem to be common amongst the models with the heaviest amounts occurring across the piedmont and tidewater regions of VA/NC. However, upslope southeasterly low level flow is still expected to enhance amounts near the Blue Ridge. Flooding will become a concern by Saturday, but the big unknown with respect runoff is how much snowmelt will take place. The snowpack may initially act as a catchers mitt with respect to rainfall intercept, delaying potential runoff, especially if temperatures and more importantly wet-bulb temperatures remain cold enough to mitigate melting. This may be the case in the mountains, but for the piedmont where warmer temperatures will occur, the chances for flooding are much higher. Hydro ensembles continue to show a robust response particularly along the Dan river so there is growing concern for potentially significant flooding Friday night and into the weekend for at least some of our rivers. The vertically stacked closed low is forecast to move directly over the region by Saturday night, keeping a good chance of showers around with potential for some wet snow mixing in at the higher elevations west of the Blue Ridge late Saturday night. Temperatures will remain below normal through the end of the week before trending upward a bit once the wedge breaks later in the weekend. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 200 PM EST Wednesday... Cutoff low will continue to impact the region Sunday. Even though model simulations indicate the deeper moisture gets shunted to our east, the presence of the cold pool aloft associated with the upper low will result in scattered to numerous showers, with mainly rain showers in the lower elevations Sunday, and potential for rain mixing with or changing to snow showers across the mountains. A northern stream shortwave is expected to give the cutoff low a boot off the coast Monday with colder but dry weather resuming for next week. && .AVIATION /04Z THURSDAY THROUGH MONDAY/... As of 1140 PM EST Wednesday... Lower clouds within deep westerly flow continue to push east across the region except in the southeast where downsloping is acting to clip moisture crossing the foothills. This ahead of a weak cold front that is pulling low level moisture northeast into more of an upslope regime tonight. This supports MVFR ceilings at KLWB/KBLF and perhaps at times at KBCB. More in the way of VFR ceilings are expected at KROA/KLYH and only scattered clouds around KDAN overnight. As the shallow moisture increases cant totally rule out IFR ceilings espcly at KBLF with some light drizzle and possibly freezing drizzle along the far western slopes. However for now confidence/PoPs remain low so keeping out any precip mention at this point. Dry weather will continue into Thursday with warm advection helping to scour out low level moisture leaving mostly VFR during the afternoon. Moisture well in advance of a deepening low pressure system to the southwest will increase Thursday evening with potential for southeast flow upslope flow to produce MVFR/IFR ceilings prior to midnight along the Blue Ridge. Ceiling heights and exact timing of changes for the mountain location is low to medium, however confidence is fairly high that VFR conditions will prevail throughout for eastern locations. Extended Aviation Discussion... A strong low tracks across the southern United States at the end of the week. There are some timing differences in the models but at this point the widespread rain and associated sub-VFR conditions will be very late Thursday night into Friday. This ahead of the low and a strong coastal warm front that will aid lift across the region on Friday and result in widespread rain and likely IFR or worse conditions by afternoon. Upper low may then linger Friday night into Saturday with potential MVFR/IFR lingering to start the weekend as added bands of showers work north ahead of the upper system. Sct MVFR conditions in showers and low clouds are still possible in the west on Sunday in the wake of the departing upper low. Improving conditions to VFR will then be on tap for Monday. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH NEAR TERM...JH/KK SHORT TERM...PM LONG TERM...PM AVIATION...JH/JR/KK

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