Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 201501

Area Forecast Discussion
National Weather Service Blacksburg VA
1001 AM EST Mon Feb 20 2017

High pressure will build over the region today and remain in
place through at least Tuesday. A weak cold front will approach
the area from the west Tuesday night before weakening across
the mountains on Wednesday. A warm front will move north through
the region Thursday into Friday.


As of 1001 AM EST Monday...Visible satellite still reveals
ongoing stratus/fog across most of southeastern West Virginia
(excluding Mercer County). Low visibilities were still noted in
recent LWB METARs in the fog. While it has been slower to burn
off than initially anticipated due to some high clouds, high
cloudiness has begun to erode and should allow for sun to mix it
out through the rest of this morning.

Otherwise, I`ve tried to raise dewpoints through this morning
which are currently well into the 30s to mid 40s. However,
expect these to lower by late morning into the afternoon as
mixing of dry air aloft begins. It should be a great holiday for
those outdoors today with temperatures well into the 60s to
lower 70s, plentiful sun and light winds.

Previous near-term discussion issued at 218 AM follows...

Another very mild day for late February in store today as strong upper
level ridging builds overhead while surface high pressure bridges south
just east of the mountains later this afternoon. This coupled with high
heights and warm 850 mb temps under strong insolation despite some high
clouds, should allow highs to reach the 60s west to lower 70s east. Low
level flow turning more southeast later in the day likely to keep
values a bit more uniform as well with slight cooling noted aloft out
east later today and downslope warming into southeast West Va.
Therefore appears best shot at record highs mainly over the south and
west per the CLIMATE section below. Otherwise few changes other than to
include a bit more western fog/low clouds to start that should quickly
erode this morning with heating under dry air aloft.

Ridging aloft remains in place overnight with surface high pressure
becoming more wedge oriented as it slips southeast to along the Mid-
Atlantic coast late. Influx of sheared high/mid cloudiness coming
through the mid level ridging from showers well to the west likely to
become more widespread after midnight as suggested by most guidance.
Also low level southeast flow turning westerly with height could produce
a ribbon of low clouds along the Blue Ridge by daybreak but iffy
given such weak flow/subsidence. Thus keeping things more of a
partly cloudy flavor for now given mid level dryness seen on progged
cross sections, and model tendency to be overdone with high clouds
through strong ridging that will be overhead late. Warmest air
will again be over the far west with the cooler wedge out east
per onshore flow overnight. However think weak enough for some
decoupling espcly outlying areas, while the ridges likely to
keep some mixing. This supports a range of lows from near 50
higher western ridges to 30s/low 40s valleys/east, while keeping
mostly 40s elsewhere in between.


As of 240 AM EST Monday...

The upper level ridge will move offshore Tuesday afternoon with
zonal flow to follow Tuesday night. Within this zonal flow, a weak
cold front will move across the Ohio Valley and over the central
Appalachian Tuesday night. This front will help bring rain showers
to the area after midnight then exits Wednesday afternoon. This
front is initially lacking moisture, but will get hydrated with the
help of an open Gulf and an ejected short wave tracking over the
Tennessee Valley. This short wave will track out of the Gulf ahead
of a closed low and gets caught in zonal flow, moving into North
Carolina Wednesday. Models are in agreement with taking the short
wave and measurable rainfall south of the area Wednesday night.
However, an insitu wedge will follow with gray drizzly conditions
possible Wednesday night and Thursday. The chances for rain
returning Thursday increases as insentropic lift associated with a
warm front aloft tracks to the north and over the wedge.

Temperatures during the period will remain warmer than normal.
Tuesday looks to be the coolest day with rain and easterly flow in
the area. Temperatures Tuesday will be in the low to mid 60s across
most of the area with upper 50s along ridgetops. Once we break out
of the rain Wednesday afternoon, temperatures will jump into the
upper 60s to mid 70s. Thursday will be a tricky forecast with
temperatures. They could be similar to Tuesday or to Wednesday. Even
though the models are showing an insitu wedge over the region, they
also have southerly flow and temperatures warming into the upper 60s
to mid 70s. If the insitu wedge does linger through the day
Thursday, thick low clouds, easterly flow, and light rain/drizzle
could keep temperatures down into the lower to mid 60s areawide.
Until confidence increases on the scenario for Thursday, we will
stick close to model guidance.


As of 235 PM EST Saturday...

Per WPC, not much weight put on the GFS, especially Friday through
Sunday, as it is faster with most of the synoptic scale features
than much of the other guidance. Timing of the cold frontal passage
still similar with the front coming through Saturday morning.

00Z ECMWF had colder air behind the front just brushing through the
Mid Atlantic region, which was not nearly as cold and as far a push
south as previous runs. High temperatures will still drop about 10
degrees but coldest air will start moderating after Sunday morning. A
low level jet and cold air advection will result in strong gusty
winds behind the front into Sunday morning.


As of 610 AM EST Monday...

Low clouds and fog will persist in spots across the western
locations early this morning with IFR/LIFR cigs/vsbys primarily
at KLWB and MVFR possible KBLF/KBCB vicinity.

Further east will be VFR.

The low clouds/fog should dissipate by mid morning if not sooner
with periodic high/mid cloud canopy expected under
light/variable to easterly winds the rest of the day.

Moisture will continue to increase overnight with VFR high/mid
cloud cigs overnight at most locations. Also some strato-cu may
develop along the Blue Ridge late as onshore flow increases, but
too uncertain to include any lower cigs at this point tonight.
Fog/stratus likely quite spotty overnight as well unless less
high level cloud cover is realized allowing low level
saturation across the valleys such as KLWB/KBCB.

Extended Aviation Discussion...

Expect overall VFR to prevail through much of Tuesday as a weak
cold front to the west remains slow to move east with potential
for MVFR cigs to arrive mainly across the mountains later in the
day. However will have to watch possible MVFR level low clouds
earlier along the Blue Ridge as a weak low level wedge develops.

Showers and likely sub-VFR to develop Tuesday night into early
Wednesday with an axis of showers preceding the weakening cold
front arriving from the west. Expect showers to decrease
Wednesday afternoon and night while leaving residual MVFR cigs
in place. Later Thursday into Thursday night, low confidence of
patchy light rain returning to the area, with cigs and vsbys
remaining mainly VFR except for ocnl MVFR across southern and
western sections.

Friday, moderate confidence in precipitation trending more
showery, as the low level jet increases in advance of a strong
cold front. Expect a mix of MVFR and low end VFR ceilings and
mainly VFR visibilities. Surface wind gusts of 20 to 30 kts
possible across the higher terrain. Band of showers with the
front to arrive Friday night into early Saturday followed by drier
weather and increasing northwest wind by afternoon behind the


As of 315 PM EST Sunday...

Record High Temperatures and Year of Occurrence

Feb 20
Blacksburg, VA..68 in 1984
Bluefield, WV...67 in 1986
Danville, VA....74 in 1971
Lynchburg, VA...76 in 1930
Roanoke, VA.....75 in 1939




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