Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 210152 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 852 PM EST Sat Jan 20 2018 .SYNOPSIS... High pressure just south of the area tonight will drift east and offshore on Sunday allowing for a continued warm west to southwest flow across the region into Monday. A strong cold front approaches from the west Monday before crossing the area Monday night into early Tuesday. High pressure then follows the front resulting in colder temperatures on gusty northwest winds into midweek. && .NEAR TERM /THROUGH SUNDAY/...
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As of 845 PM EST Saturday... A much milder night ahead than many seen over the past week with the combination of higher dewpoints/mixing in conjunction with a warming airmass to keep lows mostly above freezing outside of the deepest valleys. Otherwise still seeing some low clouds invading the far west associated with return flow along a weak boundary heading back north. Despite very dry air aloft, expect some of this cloudiness may sneak east of the mountains per moisture advection, as should also see the downsloping 85h jet weaken overnight. Thus appears skies likely to remain mostly cloudy west with low clouds filling in under the inversion, and clear to partly cloudy east. Nam continues to produce light rainfall over the far west as well overnight but given only a shallow layer of moisture aloft off evening soundings appears too wet. Latest HRRR does have some spotty rain or sprinkles northwest late under the continued westerly flow convergence so left in some low pops very late and removed elsewhere. Fog still looks iffy but kept in far south where dewpoints remain the highest over spotty snow cover. Lows look to be mainly in the 30s with some 20s deepest valleys. However if winds stay up just a little and clouds head farther east, then likely to see some spots stay in the 40s all night. Previous discussion as of 309 PM EST Saturday... Arctic high pressure across our region will slowly drift east tonight and push off the North Carolina coast Sunday. Ahead of low pressure in the central United State, moisture was tracking northeast from the Gulf. Lower clouds associated with this moisture were pushing into western portions of our forecast area. A few showers are possible in the west tonight as a warm front lifts north through the region. With light winds and low level moisture, decided to add some patchy fog to southern portions of the forecast area. Overnight low temperatures will range from around 30 degrees with snowpack to near 40 degrees along the ridges. The closed upper low over the Midwest will open up and moves into New England early next week. High pressure will push out into the Atlantic ocean Sunday resulting in a warm southwest flow. Isolated to scattered showers are possible in the northwest Sunday morning. High temperatures on Sunday will vary from the upper 40s in the mountains to the lower 60s in the piedmont.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/... As of 309 PM EST Saturday... Warm front lifts north Sunday night into Monday with warm advection and southwest flow increasing. Will see some sun in the east Monday though cloudiness will move in aloft quickly ahead of the front. Models overall still advertising a line of showers, low topped with limited instability. Shear is high and shallow convection seems likely where winds aloft gust to the surface along the line of showers. At the moment SPC has not threat of severe, but cannot rule out some strong winds Monday evening/overnight, mainly southwest over the NC mountains/foothills. Will see area of showers lift out by midday Tuesday with lingering rain showers in the west. Colder air arrives Tuesday afternoon in the mountains with a few snow showers possible but moisture appears to dry out fast. Expect post-front winds Tuesday to possibly reach advisory levels along the Blue Ridge with 8h jet of 40-50kts and 4-6mb 6 hr pressure rises. Cloudiness may inhibit some of the stronger gusts. These winds along with potential gusty winds with showers will be mentioned in the HWO. Temperatures in the 50s to around 60 Monday cool to the 40s Tuesday in the mountains with falling temps over the higher terrain. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 130 PM EST Saturday... Overall pattern stays progressive with shortwave moving across midweek with limited moist, with brief cool down, but still close to normal temps for late January. 5h heights build late in the week while, strong trough shifts into the western U.S. As this strong trough moves into the middle of the country Saturday, southwest flow increases over us with moisture shifting toward our area. Surface high should be off the mid- Atlantic coast, but in-situ type wedge seems to set up allowing for potential of wintry mix during Saturday although at the moment will carry mainly rain, mixed at times with snow, and overall looks like Sat night-Sunday are wetter with wedge breaking. && .AVIATION /01Z SUNDAY THROUGH THURSDAY/... As of 610 PM EST Saturday... SCT to BKN MVFR clouds in the western mountains will spread east to the Blue Ridge this evening and perhaps east of the mountains tonight. This should result in periods of VFR to MVFR cigs at times from KBLF/KLWB east to KBCB, including at least scattered at KROA, and perhaps KLYH. As moisture increases, expect to see cigs lower further around KBLF overnight with IFR- LIFR cigs possible late tonight into Sunday morning. Visibilities are expected to be mostly VFR through the TAF valid period. However, if the ceilings drops below 005 at KBLF, MVFR visibilities in fog/mist will be possible. MVFR conditions may continue in the west Sunday, while VFR is expected in the east. Westerly winds at 10-20 kts mountains, and around 10 kts out east will diminish to less than 10 kts across most of the mountains, while becoming mainly light east of the Blue Ridge. However a few gusts may linger across the higher ridges as the jet aloft remains strong until late tonight. This may also result in areas of LLWS especially At KROA and KBCB this evening as surface winds decrease. Best axis of low level moisture will reside over the western sections on Sunday as decent westerly flow continues. Some of this may keep sub-VFR cigs going into mid or late morning west of the Blue Ridge with at least scattered low clouds out east into the afternoon. However moisture pinned in against the mountains may keep KBLF/KLWB MVFR at times well into the afternoon. Isolated showers may also track in from the west across far northwest sections on Sunday, but since iffy and mainly west of KLWB wont include mention. West winds should be much lighter on Sunday with speeds of 5-15 kts before backing southwest during the afternoon. Low confidence in ceilings, with medium confidence in visibilities and winds through the TAF valid period. Extended Discussion... Sub-VFR conditions will likely redevelop at least across the mountain locations Sunday night and across the entire area Monday afternoon into Monday night as a cold front and its associated precipitation approaches/arrives. Strong convective showers are expected with this front, including a potential QLCS and isolated thunderstorms. Should see a return to VFR east of the mountains by Tuesday afternoon with lingering upslope driven MVFR cigs across the western mountains into Tuesday night. Very gusty northwest winds return to the area as well Tuesday night into Wednesday on the backside of the departing system. Snow showers could also bring periods of sub-VFR vsbys Tuesday afternoon and night across the SE West Virginia sites thanks to strong upslope flow and residual low level moisture. High pressure should build in resulting in drier weather and diminishing winds on Thursday. && .EQUIPMENT... As of 325 PM EST Friday... NOAA Weather Radio, WXL60 (Roanoke Transmitter) which broadcasts at 162.475 MHz remains off the air. The phone company reported that the circuit line had been cut and will take until Monday January 22nd to fix it. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH NEAR TERM...JH/KK SHORT TERM...WP LONG TERM...WP AVIATION...JH/KK EQUIPMENT...WP

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