Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
958 PM EDT Friday Oct 9 2015
a cold front will pass through the area this evening...associated
with showers and a few thunderstorms. This front is expected to
stall along the southeast Atlantic coast Saturday...becoming the
focus for an area of low pressure which will develop along the
coast and remain nearly stationary for the remainder of the
weekend. Meanwhile...high pressure will build across the Ohio
Valley and into New England Saturday...and wedging south along the
east side of the Appalachians by Sunday.
Near term /through Saturday/...
as of 945 PM EDT Friday...
Latest surface analysis indicates the cold front is moving
southward across the Alleghany Highlands and southeast West
Virginia this evening. Expect the front to continue passing across
our area into the early morning hours of Saturday. Convection
ahead of the boundary has weakened to a broken band of showers
passing across the Piedmont...occasionally with a rumble of
thunder...while spotty rain continues across the mountains.
While convection will continue to weaken into early Saturday
morning...the precipitation threat is expected to linger
overnight...mainly south of Highway 460...per the front stalling
and a wave of low pressure developing along the front vicinity of the
South Carolina coast Saturday.
Challenge Saturday will be whether precipitation will completely
clear the County Warning Area. Model consensus is for areas along and south of
Highway 58 to maintain at least chance probability of precipitation...with likely to
categorical probability of precipitation across the Carolinas. Clouds will persist
throughout the day...with potential for some clearing across the
northern County Warning Area as drier infiltrates the region from the north...high
pressure building from the Ohio Valley into New England.
Temperatures will remain relatively mild until the frontal passage
later this evening. Lowering dewpoints and cold air advection
behind the front will then result in about a 10-15 degree drop
thereafter. Saturday will likely be a cool day due to lingering
cloud cover...highs struggling to get above 60...down 15-20
degrees compared to Friday.
Short term /Saturday night through Monday night/...
as of 330 PM EDT Friday...
Digging upper trough will evolve into a cutoff low vicinity of the
South Carolina coast Saturday night. This feature is then expected
to linger until the arrival of a northern stream trough Monday
night... this trough acting as a kicker and booting the stationary
low away from the coast. Until this takes place there will likely
be a persistent area of cloud cover across the eastern Carolinas
and threat for rain along the coast. For our forecast area it
appears the low will be just far enough east to keep rain out of
the forecast. However...clouds may linger across our southeast
counties or at least be viewable on the southeast horizon until
the low finally moves far enough offshore.
With sunshine returning to most of the County Warning Area...expect temperatures
to warm well into the 60s Sunday...possibly testing 70... then
into the 70s Monday. Overnight lows will be in the 40s...with a
chance to dip as low as the upper 30s in some of the mountain
valleys of the Virginia/WV Highlands Sunday and Monday mornings.
Long term /Tuesday through Friday/...
as of 345 PM EDT Thursday...
Fast moving positively tilted upper level trough is expected to
move across the forecast area Tuesday. Associated surface cold
front will quickly move across the forecast area with chance threat
for showers. After Tuesday...the remainder of the week looks dry
as broad cyclonic flow over the eastern Continental U.S. Results in mainly
dry west-northwest flow aloft and no indication of moisture returning from
the Gulf or Atlantic. A broad area of surface high pressure is
forecast to extend from The Rockies east across the MS/Tennessee
valleys. This will favor near to slightly above normal
temperatures for the middle Atlantic.
Aviation /02z Saturday through Wednesday/...
as of 800 PM EDT Friday...
Latest radar imagery indicates the line of showers and isolated
embedded thunderstorms within are beginning to break up as they
push downslope off the Blue Ridge. However...modest instability
remains across the Piedmont...and may see a brief flare up in
convection through 10/03z.
A cold front will enter the area before 10/04z...and push quickly
to the southeast...with high pressure building east across the
Great Lakes region. Weather forecast models continue to indicate
the upper trough supporting the cold front transitioning to a cut
off low that stalls along the Carolina coast by Saturday evening.
As this occurs...will see a induced wedging pattern develop toward
dawn on Saturday...with winds veering from northwesterly to
northeasterly around sunrise...eventually becoming easterly during
Northeasterly to easterly windflow will support ceilings lowering
to high IFR/MVFR toward dawn Saturday...and expect these low
ceilings to persist through most of the day. Pockets of drizzle
and fog are also expected...especially where the low clouds meet
the higher terrain. In addition...the upper trough/low will
trigger areas of light rain that will at times limit visibilities
to the 2sm to 5sm range.
High pressure builds into the area behind the front Saturday
night through Monday...with most locations experiencing VFR
conditions early Sunday. On Tuesday...another cold front is
forecast to cross the area. Look for a return of scattered showers
and pockets of sub-VFR conditions.