Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 132327

Area Forecast Discussion
National Weather Service Blacksburg VA
727 PM EDT Fri Oct 13 2017

High pressure will continue to wedge southward along the eastern
slopes of the Blue Ridge tonight before eroding by Saturday
afternoon. A cold front will arrive during Sunday night into
Monday. High pressure should return to provide cooler and drier
weather for most of next week.


As of 700 PM EDT Friday...

The forecast heading into the evening, cloudy skies still
persist across the vast majority of the area. Parts of southeast
West Virginia are seeing breaks in the cloud cover. Limited
cloud cover still exits across Tazewell and Smyth Counties of
southwest Virginia. As the evening progresses, these area too
are anticipated to see cloud cover expand.

Light rain and/or patchy drizzle still is expected overnight,
especially areas along and near the crest of the Blue Ridge.

Have made minor adjustments to temperature, dew point, wind, and
sky cover to reflect the latest observations and expected trends
through the evening.

As of 220 PM EDT Friday...

While high pressure wedges southward along the eastern slopes of
the Blue Ridge, the resulting cold air damming pattern has kept
skies cloudy with patchy drizzle and isolated showers for the
afternoon. Temperatures are sluggishly moving upward, and highs
will pretty much be in the 60s for most locations. Locations
west of the wedge like far southwest Virginia and southeast West
Virginia could reach the mid 70s where more sunshine will exist.

By tonight, moisture will remain trapped below the subsidence
inversion. Expect patchy fog and drizzle to persist through the
night into Saturday morning. Lows should mainly be in the 50s.
The moisture near the surface should lessen enough to stop the
drizzle and fog around 10 AM. Temperatures will struggle to
rise at first under cloudy skies, but the wedge should erode
after midday. A rapid clearing and warming will take place from
west to east. High pressure and considerable ridging aloft will
allow high temperatures to jump into the 70s by the late
afternoon. The timing of when this jump occurs does make the
prediction of the highs a little uncertain as there will be a
sharp gradient between sunshine and cloud cover.


As of 340 AM EDT Friday...

With the wedge out of the area and a strong subtropical ridge
building back over the area from the south, increasing
southwest flow in advance of an approaching front/upper trough,
unseasonably warm temperatures will return to the area. Maximum
temperatures Sunday will likely run 15-20 degrees above normal
with 80s across much of the forecast area, 70s in the higher

A frontal system will approach the area from the northwest late
in the day, possibly moving into the western mountains before
sunset. Even with limited moisture, strong forcing should
support a narrow line of showers with the front, largely behind
the front. While the front appears on all models to be about 6
hours slower than earlier thought, still expecting all areas to
see some showers, mainly west of the Blue Ridge overnight and
into Monday morning across the Piedmont. QPF will be light and
largely less than 1/4 inch.

The remainder of the forecast period will trend much more toward
typical fall weather as compared to our recent period of
extended summer. 850mb temperatures will drop down into the
single digits by Tuesday, allowing low temperatures to drop into
the 30s in the mountain valleys and 40s across the Piedmont.
While this is not particularly unusual for mid-October, it is
much cooler than anything we have seen for a while. Locations
such as Burkes Garden will likely see a light freeze and frost
is a possibility as well, especially with greater moisture in
the ground compared to cool spells in October. Will include
patchy frost around Burkes Garden on the coldest morning,
Tuesday morning.

Other than the chance of rain Sunday night/Monday morning, look
for abundant sunshine and dry conditions through the period.
Temperatures trending from well above normal at the beginning to
below normal at the end.


As of 350 PM EDT Friday...

High pressure at the surface and aloft will remain and build over
the area through the entire period. Only the GFS hints at a
possible upper-low pressure off the coast late in the period.
Even if that occurs, the moisture will remain well east of our
area. Otherwise, a very dry air mass with strong subsidence will
prevail through the period. 850mb temperatures will slowly
recover back into the +15C range by the end of the period
allowing temperatures, below normal at the beginning, to be near
to slightly above normal by the end of the period. Have kept pop
values at 0% through the entire period.


As of 720 PM EDT Friday...

MVFR/IFR ceilings over a generous portion of the area, along
with some patchy light MVFR/VFR light rain and drizzle will
trend to LIFR/IFR ceilings and IFR/MVFR visibilities as the
night progresses within a region of cold air damming. This
scenario is currently impacting all but the area along and west
of KBLF-KMKJ line. However, this area too is expected to
experience sub-VFR conditions as the night progresses.

During the day Saturday, sub-VFR conditions will slowly improve
through the morning hours. However, by the early afternoon, all
but only a few locations will be experiencing VFR conditions as
the lee side wedge erodes.

Extended Aviation Discussion...

VFR conditions will persist Saturday night into Sunday. A cold
front will arrive by Sunday night to bring a chance of showers
with accompanying MVFR/IFR ceilings and visibilities into
Monday. The cold front should head offshore on Monday night,
which will allow conditions to improve to VFR by Tuesday. High
pressure will return to provide good flying weather through the
rest of the week.




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