Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 280948

Area Forecast Discussion
National Weather Service Blacksburg VA
448 AM EST Tue Feb 28 2017

High pressure along the Mid-Atlantic coast will continue to move
further east away from the region. A warm front, located across
the southeast states this morning, will lift northward through
the day in association with a weak upper-level disturbance
tracking toward the Ohio Valley. A strong cold front will then
move through the region from the west late Wednesday accompanied
by showers and thunderstorms, then followed by blustery and
much colder conditions for the end of the week.


As of 420 AM EST Tuesday...

High pressure located just off the Mid-Atlantic coastline will continue
to drift further out to sea today. Near zonal flow aloft will begin
to buckle and amplify as a strong Pacific-based system shifts eastward
off the west coast of the U.S. Short wave ridging will evolve across
the eastern U.S. through the day today allowing a warm front, located
across the southeast states, to lift northward. This in conjunction
with an upper disturbance tracking from the Southern Plains toward
the Ohio Valley will support showers developing and spreading
into the forecast area during the afternoon/evening hours, then
moving primarily north of the area overnight. As the warm front
lifts through the region during the late afternoon/evening,
dewpoints will climb from the 30s/40s into the 50s as warm/moist
air tracks northeast from the Gulf. There will be a small
window of opportunity across far southwest VA and extreme
southern WV, generally west of I-77 for isolated thunderstorms
during the late afternoon toward 00Z as thunderstorms move
northeast along the I-81 corridor from northeast TN. Even though
the entire CWA, with the exception of some of the NC counties
are outlooked for general thunder, feel that this is the primary
region where such could occur. Instability is quite limited,
although dynamics are decent and shear is notable.

Expect a big warmup by afternoon as the warm front moves into the
region. 850mb temps, still in the single digits this morning, will
recover into the low teens, say +12C to +14C, by afternoon/evening.
This will yield max temps in the 60s west to 70s east today. Minimum
temperatures Wednesday morning will be very mild with the entire
region in the warm sector ahead of the next front along with
low end gusty warm, moist south-southwest surface winds. Minimum
temperatures Wednesday morning will only be in the 50s west to
even lower 60s Piedmont, some 20+ degrees above normal for the
first day of March.


As of 400 AM EST Tuesday...

A large-scale mid-level trough over the central United States will
move eastward into the Ohio/Tennessee Valleys early Wednesday, then
across the Mid-Atlantic states Wednesday afternoon and evening.
A 100+ kt 500-mb speed max will translate generally eastward from
the OH Valley through New England and the Mid-Atlantic region during
the period. In the low levels, a surface low is forecast to develop
northeastward from near Detroit to the northern parts of New England
by Wednesday night, it`s associated cold front racing east across
the OH/TN valley Wednesday morning, then across the Appalachian
Mountains and the Mid-Atlantic States Wednesday afternoon and
evening, passing off the east coast by daybreak Thursday.

Per timing of front across our forecast area, which appears it will
occur during peak heating, concern for severe weather exists with
potential for damaging winds.  A strong deep-layer wind field of
southwesterly flow from 50-60 kts at 850 mb and increasing with
height to 70-100 kts in the midlevels, supports the development of a
fast moving squall line, and/or linear organized storm clusters.
Some tornadic risk may develop as the squall line matures, but
greatest threat attm appears that it will come from damaging wind
gusts associated from what appears to be an environment that will
favor a QLCS.

Overall risk assessment by the Storm Prediction Center places the
entire CWA under a Slight Risk for severe storms Wednesday,
deferring higher probabilities due to uncertainties with exact
timing of squall line and available CAPE.  It still appears that
onset will take place across areas west of the Blue Ridge between
Noon-4PM, then translating east of the Blue Ridge and across the
foothills and piedmont between 4-9PM. Due to the fast nature of the
front, this will limit overall QPF...model guidance entertaining
0.25 to 0.75 of an inch of rain.

Temperatures Wednesday will be unseasonably warm with readings in
the 70s, and possibly eclipsing 80 in the piedmont... then take a
nose dive behind the front with about a 25 degree drop, yielding a
much cooler day Thursday, although still slightly above normal.

Pressure rises post frontal support near advisory non-convective
wind gusts (40 kts) in the higher elevations Wednesday night.  Will
highlight this in the HWO, but think bigger story will be convective
wind threat from Wednesday`s prefrontal deep convection.

Some increase in clouds anticipated late Thursday night across WV
ahead of a southeast moving front, although precip production
appears low due to limited moisture. Aside for some snow showers
skirting the WV highlands by daybreak Friday, the remainder of the
CWA should remain dry with temperatures retreating closer to normal.


As of 430 AM EST Tuesday...

Secondary shot of cooler air arrives with a clipper like front from
the northwest Friday. Appears best lift/moisture will stay north of
the CWA, so only low chance pops for snow showers across the
mountains of Southeast WV into the Alleghany Highlands of VA.

Winds should speed up behind this system Friday afternoon but 8h
wind stay under 50kts, and pressure rises are marginal, so most
gusts will be under advisory levels.

Expect high pressure overhead Saturday to provide close to normal
highs for early March ranging from the lower to mid 50s over the
area, with some 40s in the mountains.

Keeping it dry Sunday with milder temperatures as high pressure
moves southeast off the Southeast coast. A front enters the northern
tier of the U.S. the slides southeast to the Ohio Valley by Monday.
Will see warmer temperatures Sunday-Monday with shower chances
increasing Monday.


As of 1120 PM EST Monday...

A weak upper level disturbance producing a high level strato-cu
cloud deck will continue to push east of the area overnight.
This will allow for a brief period of drying in the mid levels
of the atmosphere, providing relief for ceilings prior to the
arrival of a slow moving warm front approaching our from the
Carolinas. A transition from a 5K foot BKN/OVC deck to SCT/FEW
layers is expected during the overnight hours overnight into
Tuesday, especially for the northern/western airport locations.
These dry conditions should also limit any fog development, thus
allowing the continuation of VFR conditions through at least
the early morning hours Tuesday.

A warm front arrives on our southern doorstep Tuesday, allowing
for saturation of the lower atmospheric levels. This will act
to once again lower ceilings during the day on Tuesday. Early
indications have sub VFR conditions impacting KDAN/KLYH as early
as mid afternoon, with other sites following by Tuesday evening.
Precipitation chances also increase late in the TAF period, but
uncertainty remains on aerial coverage and intensity. For now,
have included an afternoon prevailing shower mention at
KBLF/KLWB but still VFR vsbys at this point. Also uncertainty in
just how far east and significant showers will make it later
Tuesday into Tuesday evening with some solutions keeping most
rainfall just west of the western TAF sites.  Winds shouldn`t
be much of a factor this period, remaining sustained below
10KTs, with only localized gusting along the ridges.

Overall, medium to high confidence of VFR conditions through
sunrise, with uncertainty increasing with ceilings + vsbys as
the day continues on Tuesday.

Extended Aviation Discussion...

A warm front across the southeast states will lift northeast
Tuesday night before passing to the north of the area on
Wednesday. An increase in low-level moisture will likely result
in MVFR cigs Tuesday evening, especially along and near the Blue
Ridge with moist southeast flow. A few light rain showers may
also accompany the front.

A cold front pushes east into the area Wednesday into Wednesday
night with potential for more widespread MVFR/IFR in showers
and thunderstorms. A west to east moving squall line with strong
to possibly severe thunderstorms, perhaps a QLCS type convective
configuration, will be possible late Wednesday into Wednesday
evening in advance of the front. Strong northwest winds along
with mountain sub-VFR in upslope low clouds and light precip
will likely follow the front for much of Thursday. Expect
downslope drying to return VFR to eastern locations by Thursday
afternoon with this trend lingering across eastern sections
through the end of the week. However another weak clipper area
of low pressure looks to track just north of the region by
Friday with possible mountain MVFR in at least upslope
cloudiness, and possible light precipitation western ridges
later Thursday night into Friday. High pressures builds in with
VFR expected Friday night into Saturday.


As of 330 AM EST Monday...

Record warm Mins for March 1

Roanoke.....52 in 1918
Lynchburg...57 in 1910
Danville....51 in 2012
Blacksburg..45 in 1997
Bluefield...56 in 1997

Record highs for March 1

Roanoke.....76 in 1972
Lynchburg...78 in 1918
Danville....80 in 1972
Blacksburg..72 in 1976
Bluefield...78 in 1997




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