Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 121910 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 210 PM EST Fri Jan 12 2018 .SYNOPSIS... A warm front will move north of the area this morning. This occurs ahead of a strong cold front that will approach the region from the west later today, before crossing the area tonight. Cold high pressure follows this system for later Saturday into early next week, with added chances of upslope snow showers possible. && .NEAR TERM /THROUGH TONIGHT/...
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As of 200 PM EST Friday... Have adjusted maxes based on current temperature trends. ALso added isolated thunderstorms in with gusty wind potential east of Lynchburg and Danville where MSAS analysis showed CAPES around 600J/kg and Lifted Index values around -1. Models remain consistent in bringing the next stronger surface wave across the southern Tn Valley up along the western spine of the Appalachians this evening and well to the northeast late tonight. Very strong dynamics with this feature along with strong convergence likely to result in a more concentrated band(s) of heavy rain producing showers in from the southwest by late afternoon with the heavier showers exiting across northeast sections after midnight as the associated strong cold front whips east through the mountains. This likely to bring another 1-2 inches of rain espcly west with some low topped convection possible south/east this evening given weak instability and shear. Given antecedent rainfall over the NC mountains from overnight may need to hoist a flood watch for added heavy rain for later this afternoon but will hold off for now and handle with statements/HWO since expecting a lull in rain until later this afternoon. Also included a bit more thunder over the southeast where isolated bands could precede the main axis along the front this evening. Otherwise running with a window of categorical pops from later this afternoon through mid evening from southwest to northeast before tapering to mainly upslope pops for rain to snow changeover after midnight. Very mild highs today, mostly 60s as the wedge exits and deeper warm advection wins out. Abrupt shot of cold advection to follow the front later tonight with a 15-20 deg/C drop in 85h temps over the west by dawn Saturday. Strong pressure rises along with this change in airmass supports winds near advisory mountains but given a weaker jet appears may stay just below criteria at this point, so will only mention in the HWO for now. Deeper moisture will also be streaking off to the northeast as the cold air arrives resulting in a race between it and the cold advection to whether or not more snow occurs over the far west. Latest guidance showing perhaps an inch or so possible from Western Greenbrier down to near BLF with lighter amounts farther south and flurries out to the Blue Ridge. However will need to watch for possible late night flash freeze given the quick drop in temps espcly far western sections. Should see things clearing out late across the east behind the front but lows remain tricky as exact timing of the arrival of the cold air remains a bit iffy. Therefore keeping range of lows from around 20 far west to around 40 southeast with falling temps across the board late.
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&& .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 225 AM EST Friday... A surface cold front will slide into North Carolina Saturday morning, while an upper level trough and deformation zone tracks northeast across the Ohio Valley. Behind the surface front, winds become westerly and as moisture becomes limited, rain showers will be ending or may have ended by first light. The mountains will see light snow showers/flurries through the morning, tapering off through the afternoon. The highest accumulations will be around 2 inches in western Greenbrier and maybe an inch towards Bluefield. Little to no accumulations elsewhere. Winds will be breezy through the day Saturday, but will not meet criteria for a wind advisory. These winds will usher in very cold air. Mountain temperatures may only rise 3F-5F from Saturday morning`s lows, then become steady or fall through the afternoon. Highs across the mountains will range from the mid 20s to low 30s. Temperatures east of the Blue Ridge will see highs peaking around noon with a range from the upper 30s in the foothills to the mid 40s across the piedmont. Temperatures will continue to fall overnight with lows 8F-13F across the west and upper teens to lower 20s east. Wind chill readings will be 5F-8F colder than the air temperature. Weakening winds and more sunshine will help warm temperatures Sunday. Highs west will be in the 20s and east will see 30s. Similar temperatures to Saturday night are expected Sunday night but with less winds. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 325 AM EST Friday... High pressure will make a brief stay over the region Monday, then an Arctic front, set to cross the area Tuesday (GFS) or Wednesday (ECM), will bring another round of bitterly cold temperatures to the region in the later half of the week. If this front can gather enough moisture and the area stays cold, precipitation with this front will likely be snow. The ECM is the model showing the most snow at 2 inches. The GFS only has an inch for the mountains and lesser amounts east of the Blue Ridge. Following this front, high pressure will build over the region for the remainder of the week. Temperatures will warm to near normal levels Monday and Tuesday, then fall below normal following the frontal passage. Wind chill values fall below zero across the mountains Wednesday and Thursday mornings. && .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/... As of 1245 PM EST Friday... Ceilings will be IFR to MVFR for this afternoon with bands of moderate to heavy showers across southwest Virginia, northwest North Carolina and southeast West Virginia. Conditions will be changing quickly through Saturday morning. Showers will continue until a strong cold front crosses through the area. Medium to high confidence on the timing of the wind shift from south to west and northwest. Expecting the front to reach KBLF around 04Z/11PM. The front will be past KLYH and KDAN before 11Z/6AM. Warm air over relatively colder ground had created fog in some spots today. MVFR visibilities or lower are expected with any of the heavier showers. Isolated thunderstorms are possible at KDAN between 22Z/5PM and 03Z/10PM but probability was too low to include in the TAF. Behind the front drier air comes in east of the Blue Ridge and across the foothills. Models were suggesting some residual MVFR clouds and low level moisture in central and eastern Virginia Saturday so clearing may be slower at KDAN and especially KLYH. Snow showers develop at KBLF/KLWB as temperatures drop tonight. Northwest winds will ramp up behind the front overnight with gusts to 25-35 knots possible over the mountains. Be alert for rain that falls today to freeze overnight on runways/taxiways as the temperature drop below freezing. Extended Discussion... Snow showers will end by Saturday night over the mountains. and northwest winds will diminish. VFR across the region Sunday. MVFR snow showers are possible Monday night and Tuesday, mainly over the western locations with the passage over a clipper system. This will lead in a surge of arctic air. && .HYDROLOGY... As of 400 AM EST Friday... Rainfall amounts over the past 24 hours have ranged from 3-4 inches across parts of the NC mountains to an inch or two along the remainder of the Blue Ridge, to less than an inch elsewhere. This has led to minor flooding across parts of Watauga county perhaps partly due to ice issues and fast runoff. Expecting steadier rainfall to taper off from south to north this morning before another round of heavier showers arrives from the west later today into early this evening. This may bring another inch or two of rain to the mountains and perhaps upwards of an inch east of the Blue Ridge. Pending how fast soils recover along the Blue Ridge, this could lead to added problems farther north by this evening so something to watch. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH NEAR TERM...AMS/JH SHORT TERM...RCS LONG TERM...RCS AVIATION...AMS/JH HYDROLOGY...JH is the U.S. government's official web portal to all federal, state and local government web resources and services.