Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 122104 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 404 PM EST Fri Jan 12 2018 .SYNOPSIS...
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A strong cold front will cross the region this evening along with bands of moderate to heavy rain. Gusty winds and much colder air come in behind the front, along with a mix of winter precipitation in the mountains. A second surge of arctic air comes in behind a cold front that passes through the area on Monday night and Tuesday.
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&& .NEAR TERM /THROUGH SATURDAY/...
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As of 340 PM EST Friday... Following two main bands of showers over southwest Virginia, northwest North Carolina, and southeast West Virginia. The first is a more meso-scale band oriented north to south that had passed east of Lynchburg and Danville. CAPES in this area were around 800 J/Kg. The next is broad band of showers along and ahead of a cold front that extended from western Pennsylvania to near the Tennessee/North Carolina border to southwest Georgia. This front will cross through the area between 5PM and midnight. Combination of cold air advection and pressure rises will lead to gusty winds. This will enhance upslope snow showers. There will be a brief transition from rain to freezing rain to sleet then snow as cold air comes in. Bufkit soundings show more support for sleet than any other precipitation type in the transition period. Winter Weather Advisories have been posted where the temperatures drops below freezing by morning. Between the light snow and ice amounts and the freezing of any wet roads, travel will be hazardous later tonight into Saturday morning. Dry slot and clearing works into the foothills and piedmont on Saturday but models now have some lingering low level moisture in central and eastern Virginia on Saturday morning so have probability of precipitation ending a bit later east of Lynchburg. Temperature trend for Saturday will be non diurnal. Maxes for the day will be around midnight tonight.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
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As of 255 PM EST Friday... Saturday night the northwest flow weakens and moisture becomes very shallow so do not expect any lingering upslope snow showers in the far west. However with very cold airmass back in place and potential decoupling in deeper valleys by morning could see temps bottom out in single digits some mountain locations and lower to mid teens in some Piedmont locations. Where a little wind stays up along ridges expect some sub-zero wind chills, but most mountain locations will be into single digits. May not quite need wind chill advisory for a few mountain locations but will keep an eye on. Otherwise dry but cold conditions remain through Monday as surface high pressure drifts eastward across the central Appalachians. Highs and lows generally running about 10 deg below normal through this stretch, with some moderation in lows by Monday night as some southwest flow increases on back side of high ahead of a clipper system and associated arctic front approaching from the west.
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&& .LONG TERM /TUESDAY THROUGH FRIDAY/...
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As of 320 PM EST Friday... The above mentioned clipper and arctic front should move through the Appalachians on Tuesday, with GFS still slightly faster than ECMWF but for that far out in time the models overall are in fairly good agreement. However the trends with the 12Z cycles suggest a better potential for more deeply digging trough and surface wave developing along the Atlantic coast by Wednesday with some jet dynamics contributing to deeper lift on NW side of the developing surface low, which could then result in at least some light snow mainly east of the Blue Ridge. Of course as the clipper moves into the western Appalachians we expect fairly high potential on Tuesday and into Tues night for at least some light snow accumulation, but models have been trending lower on this aspect and upslope flow i s relatively weak actually. Obviously details of this entire evolution will need to be monitored as trends could still shift more progressive with the developing wave and keep any snow well east of our forecast area, but could also trend deeper, stronger, and farther west. If anything, the latter is more likely but still not especially confident this far out. For now have only gradually increased precip chances mainly for the east into the low chance category for late Tuesday night and into the day Wednesday. Most likely there will be fairly significant adjustments to the forecast as we get into early next week. While confidence may still be low in the evolution of this potential system and the overall precip chances, confidence is quite high that any precip would be in the form of snow for all locations. Confidence is also fairly high that this upper trough will lift out pretty quickly Thursday into Friday being replaced by an upper ridge and pretty quick return of normal to even above normal airmass.
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&& .AVIATION /21Z 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. && .RNK WATCHES/WARNINGS/ADVISORIES...
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VA...Winter Weather Advisory from midnight tonight to 10 AM EST Saturday for VAZ007-009>020. NC...Winter Weather Advisory from midnight tonight to 10 AM EST Saturday for NCZ001-002-018. WV...Winter Weather Advisory from midnight tonight to 10 AM EST Saturday for WVZ042>044-507-508.
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&& $$ SYNOPSIS...JH NEAR TERM...AMS/JH SHORT TERM...RCS LONG TERM...RCS AVIATION...AMS/JH

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