Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 202314

Area Forecast Discussion
National Weather Service Blacksburg VA
614 PM EST Sat Jan 20 2018

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.


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.


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.


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.


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

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.


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.




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