Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 200455
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
1255 AM EDT Sat Oct 20 2018

.SYNOPSIS...
A cold front will approach from the northwest overnight before
passing southeast and through the region on Saturday. By Sunday
this front will be well off the southeast coast with colder high
pressure building over the area for Sunday and Monday.

&&

.NEAR TERM /THROUGH TODAY/...
As of 930 PM EDT Friday...

For the evening update, sped up timing of the rain by an hour or
two...otherwise forecast looks in pretty good shape. As of 2130,
radar indicated an area of light rain already entering the
northwestern CWA... mostly light rain with visibility above 6SM.

A broad upper level trough over southern Canada and Great Lakes
region will push a cold front from the upper Mid West tonight
to the south-central Appalachains by Saturday morning. Pre-
frontal showers are expected to cross the mountains this
evening, moving east of the Blue Ridge after midnight. The front
will catch up to these showers Saturday morning and both will
exit the forecast area by the afternoon. Estimated rainfall
amounts will be around a quarter of an inch across the Mountain
Empire of southwest Virginia into the North Carolina High
County. Around a tenth of an inch is expected across the rest of
the mountains. Given residual dry environment and downsloping
flow, a tenth of an inch or less of rain is expected over the
foothills and Piedmont counties. There is a low probability for
low-top convection to form along the front as it passes over
Southside VA late in the morning. If this convection
materializes, a quarter of an inch of rain is possible.

Mild overnight temperatures are expected tonight with a range
from the upper 40s across the mountains to mid 50s east of the
Blue Ridge. Despite the passing of a cold front Saturday
afternoon, temperatures will warm into the mid 50s to mid 60s
across the area. These temperatures are around 5F cooler than
normal.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/...
As of 315 PM EDT Friday...

Saturday night the northwest flow regime the area will be under
will experience a reinforcing shot of cold air, and a
tightening of the pressure gradient with the passage of a
secondary cold front, and shortwave trough within the broader
longwave trough pattern. Behind this feature 850mb winds are
expected to increase to the 40 to 50 kt range, and surface 6hr
pressure changes will be on the order of +6 to +9 mb. We will
need to continue to monitor for the potential for wind headline
hazards. While high wind warning criteria so far is not looking
widespread, we might have a better opportunity for a greater
part of the area to experiencing wind advisory level gusts. The
final details of that will be worked out in later shifts. For
now, the potential will be addressed in the Hazardous Weather
Outlook.

The arrival of colder air will mean a strong potential for
additional sections of our forecast area to experiencing
freezing temperatures. The area of the Northern Mountains of
North Carolina, north into portions of the Mountain Empire
region of southwest Virginia, will be under a Freeze Watch late
Saturday night into early Sunday morning to reflect this strong
potential.

The strong northwest winds across southeast West Virginia is
expected to bring some scattered upslope rain or snow showers.
The snow showers have the greatest potential of occurring over
the higher terrain of southeast West Virginia. Amounts are
expected to be on the light side with western Greenbrier County
seeing some the higher values - up to two inches.

High pressure, colder air, and weaker winds will work their way
into the region by Sunday night into Monday. Almost the entire
forecast area will have either frost or freezing conditions
forecast. The least likely candidate region will be immediately
along and near the crest of the Blue Ridge where temperatures
will remain a little warmer thanks to slightly stronger winds.

Forecast confidence is moderate for the above portion of the
forecast.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 1230 PM EDT Friday...

On Tuesday, the area will still be within a region of northwest
flow on the western extent of a longwave trough that will be
heading east through New England and mid-Atlantic region of the
U.S. Tuesday night into Wednesday, a dry cold front is expected
to cross the area with the most notable change in our weather
picture being a brief increase in gustiness. However, speeds of
the magnitude expected this coming Saturday night are not
forecast.

High pressure will settle over the area in the wake of this dry
cold front through at least Thursday.

Temperatures during the above portion of the forecast are
expected to be around, or slightly cooler than, normal.

Confidence in the above portion of the forecast is moderate to
high.

Thursday night into Friday, confidence in the forecast tanks.
While the GFS and Canadian solution continue with dry high
pressure dominating our weather pattern, their European
counterpart is very agressive in having a southern stream system
heading across the Carolinas, with its associated precipitation
advancing north into and across our region. Given the
variability of the guidance, but not completely discarding the
wetter European solution, our forecast will reflect increasing
low chances of precipitation but not advertise probabilities in
likely category Thursday night into Friday.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
As of 1253 AM EDT Saturday...

Band of showers now crossing east of the Blue Ridge with
another entering the west attm. These will continue to work east
bringing periods of rain mainly to western locations through
daybreak Saturday followed by lowering ceilings to MVFR or worse
at times at KBLF/KLWB overnight. Could also see a period of
MVFR vsbys in rain/fog across the west with mostly VFR ceilings
and vsbys expected from KROA east where rainfall is expected to
be lighter.

A cold front will cross the Appalachians Saturday morning. Rain
will end after the passage of the front with a return to VFR for
the afternoon. Anticipating a generous coverage of MVFR
ceilings and localized MVFR visibilities Saturday morning mainly
across the mountains, although could see showers linger
southeast into midday with sub-VFR possible there as well.

A secondary front associated with an upper level disturbance
will cross the mountains Saturday night. This will bring a blast
of colder air associated with MVFR Cigs and mountain snow
showers/flurries for late Saturday night into Sunday morning.


Extended Discussion...

High pressure on gusty northwest winds builds in behind the
front Saturday night into Sunday. Wind gusts at higher
elevations may be 30 to 40 knots from the northwest. Upslope
rain and snow showers are also possible in southeast West
Virginia, possibly impacting KBLF/KLWB between midnight
Saturday night and noon Sunday.

VFR returns across the region after any residual low clouds
clear Sunday afternoon. High pressure will keep it VFR into
Monday through Wednesday.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Freeze Watch from late tonight through Sunday morning for
     VAZ007-009-010-015.
NC...Freeze Watch from late tonight through Sunday morning for
     NCZ001-018.
WV...None.

&&

$$
SYNOPSIS...RCS
NEAR TERM...PM/RCS
SHORT TERM...DS
LONG TERM...DS
AVIATION...JH/PM/RCS


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