Marion, Virginia Banner
 

The Latest NWS Regional Area Forecast Discussions

Select Your Area NWS Weather Forecast Office


NWS Area Weather Forecast Discussion
County Warning Area [CWA]: RNK
Regional NWS Weather Office: Blacksburg, VA

000
FXUS61 KRNK 182030
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
330 PM EST Sat Nov 18 2017

.SYNOPSIS...
A strong cold front will sweep southeast through the region
tonight preceded and accompanied by gusty winds and scattered
to numerous showers. Much colder air on blustery winds will
arrive behind the front on Sunday, with clearing skies across
the Piedmont, but with abundant clouds over the mountains along
with some upsloping snow showers across the western flanks of
the Appalachains.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 330 PM EST Saturday...

Strong cold front moving through the OH and TV Valley will
sweep east through the Blacksburg forecast area tonight,
preceded and accompanied by scattered to numerous showers.
Instability is very limited with this feature, such that
thunder, if any, will remain isolated and likely confined to the
extreme western or southwestern portion of the forecast area
where some mid level buoyancy will be maximized.

Strong prefrontal winds approaching 45 knots just above the
developing inversion layer, and strong post-frontal winds
behind the front of the same magnitude with 6-hour pressure
rises around 10 millibars support ongoing Wind Advisories though
Noon on Sunday for the mountains and the VA foothills. Some
localized gusts to around 50 knots possible across elevations at
or above 5K feet, but see no need at the present time to hoist
High Wind Warning for this area considering limited areal
coverage.

Fast moving system should keep precipitation amounts tonight to
under one half inch, with most areas receiving a quarter inch
or less. Strong cold advection and increased upsloping should
help transition rain to snow showers later tonight across the
western flanks of the Appalachians - with a continuation through
Sunday - perhaps into the early part of the short-term period
as a second short wave trof races northeast through SE WV Sunday
afternoon into early evening.

Some spotty snowfall amounts in the 1-2" range are possible
across the highest terrain, such as at Mount Rogers, VA and
across Western Greenbrier County, WV; however, most other
upsloping areas from the mountains of NW NC north through SW VA
into SE WV should receive only an inch or less.

With the strongest cold air advection to arrive on Sunday,
expect to see temperatures flatline near freezing or even
slowly fall during the day, especially across the higher
terrain where clouds will hold fast. East of the Blue Ridge
into the Piedmont, downslope clearing and a bit later arrival
of the coldest air should allow temperatures to recover into the
lower or mid 50s.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 215 AM EST Saturday...

While snow showers are likely to be ongoing in the mountains of
southeastern WV, a secondary shortwave trough/500 mb vort max
progged to ripple through the northwest cyclonic flow likely to lead
to a brief enhancement of snow showers in southeast WV at least.
Shortwave is expected to move across the northern half of the
forecast area through midnight, with a reinforcing shot of colder
air awaiting behind it. Froude number is initially unblocked which
supports possible flurries as far east as the Alleghany Highlands in
VA early Sunday evening, but are expected to become more neutral to
blocked by overnight. The moisture layer also begins thinning out
and PoPs taper from south to north toward dry by the pre-dawn hours.
Any accumulations of less than an inch would be confined to western
Greenbrier southwest into parts of Mercer County before midnight,
with just a few flakes into the Alleghany Highlands. Passage of the
shortwave and pressure rises may initially maintain gusty ridgetop
winds into Sunday evening; though as inversion height shrinks the
mixed layer around midnight, a decrease in wind speeds and gusts
along the ridges can be expected. A rather cold night with many
areas likely to fall below freezing, with the coldest values in the
low 20s in southeast WV and the Mountain Empire region.

A broad area of high pressure then begins to settle into the region
Monday into Tuesday. Shot of colder air is brief, and low-level
temperatures begin to moderate as we tap into a modest west to
southwesterly component. It will be pretty chilly early on Monday
with apparent temperatures west of the Blue Ridge in the teens
through the morning commute, so bring along an extra layer as the
holiday workweek begins. Monday and Tuesday overall appear
uneventful otherwise with high pressure and ridging aloft in
control. May see a few high clouds intrude into Tuesday, but overall
lots of sunshine this period. Forecast calls for dry conditions
Monday with highs low 40s to lower 50s, lows mid 20s to near
freezing Monday night, and highs back well into the 50s come
Tuesday.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 300 PM EST Friday...

GFS ensemble indicates a 500 mb pattern resembling a cold season
positive Pacific-North American (PNA) teleconnection regime centered
around the Thanksgiving holiday period. This often translates to
mean troughiness at 500 mb into the central and eastern US, as
repeated shortwave troughs round the top of a large ridge across the
Pacific Coast and dig/reinforce cyclonic flow aloft. Overall an
unsettled holiday period but nothing that would significantly hamper
travel plans attm.

The GFS and ECMWF indicate show a trough in the southern branch of
the jet across the Mississippi Valley/Deep South, and a more potent
northern stream trough over the Great Lakes/Upper Midwest Tuesday
night. Both also show a weak Gulf coast low developing on an old
frontal zone around the Wednesday timeframe. Question that will
likely govern what unfolds is if phasing can occur between the two
streams. This isn`t indicated at all in the GFS, which would serve
to keep us at least partly cloudy but dry. The ECMWF on the other
hand was indicating a little more phasing in its 00z run, which
would do two things: (1) bring an area of showers further north into
the Blue Ridge and Piedmont Tuesday night/overnight and (2) tap into
colder temperature profiles behind the departing system for the
Thanksgiving holiday Thursday. Less phasing was noted in the 12z
ECMWF, so while still some level of uncertainty to be accounted for,
sided a little closer to the more temperate GFS idea for the Tuesday
through Thursday timeframe. This keeps temperatures slightly below
normal, with only a limited chance for PoPs east of the Blue Ridge
on Tuesday night. Even if the more pessimistic ECMWF solution plays
out, it still wouldn`t likely lead to any significant/impactful
weather. Kept highs for the Thanksgiving holiday only in the 40s
with partly cloudy skies and dry conditions.

Looks to be a warming/moderating trend to temperatures Friday into
the holiday weekend and will likely trend temperatures to near/above
late-November normals. Weather pattern then turns more unsettled
after the holiday weekend with a larger degree of guidance solution
spread.

&&

.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
As of 115 PM EST Saturday...

Southwest winds along with mid and higher level clouds will
continue to increase for the rest of the afternoon in advance of
an approaching cold front. Some winds before prior to and
following the arrival of the front could gust as high as 30
knots into Sunday morning, especially in the mountains, with
localized gusts in excess of 40 knots across the highest
elevations - especially tonight into mid-morning Sunday.

VFR flight conditions expected to persist at all terminal
forecast points until around or shortly after sunset today
until prefrontal and frontal lines of showers begin to arrive
from the west. These showers expected to drive flight conditions
back down into the MVFR range at KBLF and KLWB in the
01-02Z/8-9 PM timeframe, then reach KBCB by/around 05Z/Midnight.

Further east, look for ceilings to fall down to the 3-5K FT
level in the 05-09Z timeframe/Midnight-4AM tonight, but still in
the VFR range, as narrow lines of showers sweep east with the
front.

Post-frontal upsloping clouds and occasional rain/snow showers
should maintain MVFR to localized IFR flight conditions across
the SE WV terminal forecast sites for much of Sunday, perhaps
even until mid-late afternoon at KBCB. Downsloping winds east of
the Blue Ridge should maintain VFR conditions with clearing
skies elsewhere on Sunday.

Medium to high confidence in wind, ceiling, and visibility
forecasts for all terminal forecast points through the
18-18Z/1-1PM forecast period.

Extended Discussion...

Higher pressure and a weakening pressure gradient should allow
for northwesterly winds to slowly abate by late Sunday night,
along with decreasing clouds across the western flanks of the
Appalachians.Widespread VFR conditions are expected thereafter
from Sunday night into Thursday.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Wind Advisory until noon EST Sunday for VAZ007-009>020-022>024-
     032>035.
NC...Wind Advisory until noon EST Sunday for NCZ001-002-018.
WV...Wind Advisory until noon EST Sunday for WVZ044-507-508.

&&

$$
SYNOPSIS...WERT
NEAR TERM...WERT
SHORT TERM...AL
LONG TERM...AL
AVIATION...WERT

Forecast Discussion from: NOAA-NWS Script developed by: El Dorado Weather