Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 251102

Area Forecast Discussion
National Weather Service Blacksburg VA
702 AM EDT Tue Oct 25 2016

Cool high pressure will build in from the northwest today and
remain wedged along the eastern slopes of the Appalachians into
Wednesday. Low pressure crossing the Great Lakes will push a cold
front through our region on Thursday. High pressure follows the
front for the end of the week.

As of 230 AM EDT Tuesday...

Quiet weather regime under diminishing winds to prevail over the
next 24 hours as surface high pressure builds to the north today
before orienting south along the eastern slopes of the Appalachians
overnight. This should keep very dry air/subsidence in place today
with only some patchy upslope low clouds far northwest sections
early this morning. Temperatures remain quite varied attm from 30s
in the deepest valleys to as mild as around 50 on the ridges. Therefore
will maintain the going frost advisory with focus mainly in the
valleys for frost early this morning. Highs today a bit cooler
than Monday behind the front given the passing trough aloft and
more northerly flow to start. However warming of dry air along
with the flow turning more west/southwest aloft later today across
the west, supports highs at or slightly above mos which gives
upper 50s to mid 60s overall.

Main question tonight will be with the frost potential out east as
winds remain light and dewpoints dry under the surface ridging. Only
caveat appears with some high cloud potential as weak shortwave
ridging to the west helps drop a speed max through the region from
the northwest with some associated high/mid cloud canopy per
model time sections. This could be enough to keep frost mostly
patchy at best and confined to more outlying areas so including
mention near daybreak but without any advisory headlines for now.
Otherwise one of the colder nights seen so far with lows mostly
30s to low 40s ridges, except perhaps a few 20s far western
valleys, where not including any added frost/freeze headlines
beyond this morning per end of the growing season.


As of 330 AM EDT Tuesday...

We will start the period with a cool and relatively dry wedge of high
pressure east of the Appalachians bringing a mix of sun and clouds to
the region. By Wednesday night the upper ridge axis will slide by to
our east as a trof approaches from the west. The bulk of the short wave
energy in the trof looks to remain off to our north, along with the
best isentropic lift and strongest winds in the southwesterly low level
jet. This will take the surface low and bulk of precipitation through
the Ohio valley into New England, with the trailing cold front moving
through our area on Thursday. Expect this scenario will bring breezy
conditions and high chance to likely POPs for areas west of the Blue
Ridge by early Thursday with lower chance POPs further to the east
across the piedmont. While mid/upper level lapse rates are steep on
Thursday, believe best dynamics are too far removed to generate a
significant chance for thunder so will keep mention out of the grids
for now.

As the front pushes off to our east Thursday night, blustery west winds
will combine with lingering moisture to keep a chance of showers in the
mountains before the moisture starts to wane. High pressure returns for
Friday with breezy conditions and seasonable temperatures, though a bit
cooler across southeast West Virginia.

Expect temperatures in the wedge on Wednesday to be in the mid/upper
50s with low/mid 60s along the southern and western periphery.  Mixing
out the wedge on Thursday will allow temperatures to reach the mid/upper
60s east of the Ridge with low/mid 60s to the west. Readings will be a
bit cooler in the west behind the front on Friday with upper 50s/lower
60s, but some downslope will boost temps to the east with lower 70s in
the foothills of North Carolina to the mid/upper 60s across the NC/VA


As of 300 PM EDT Monday...

A low pressure system will track from the Great Lakes to New England
Friday into Saturday. The associated front with this system will slowly
move south across the forecast area Saturday and Saturday night. Since
we have a ridge blocking the Gulf and bulk of the precipitation and
energy will be with the parent low to the north, we are only
forecasting scattered light showers north of 460 and sprinkles or just
an increase in clouds south. Both the GFS and ECM are at odds with the
forecast for Sunday and Monday. For now, we will keep conditions dry.

Temperature will be above normal Saturday with areas along the VA/NC
border warming into the 70s. Temperatures cool down behind the front
Sunday but are expected to remain above normal into early next week.


As of 645 AM EDT Tuesday...

Widespread VFR under light winds expected today and tonight
with high pressure in control. However may see some late night
river valley fog across a few of the mountain valleys late tonight
espcly around KLWB where will include brief LIFR toward daybreak.
Also frost likely in the valleys with some patchy nature coverage
in the east as well around dawn.

Extended aviation discussion...

Still expecting overall VFR to continue Wednesday into Wednesday
night with surface high pressure ridging south across the region.
However some potential to see areas of sub-VFR in patchy strato-cu
espcly Blue Ridge and points east although confidence low given
such dry air in place.

Thursday...Low pressure is forecast to move across the upper
midwest and into the Great lakes with a surface front crossing the
Ohio Valley. Threat for showers and sub-VFR will be possible
along this front which would impact the central Appalachians by
Thursday afternoon. However given best support passing to the
north and limited moisture, expecting best potential for lower
cigs/vsbys to occur across the western mountains and across
northern portions of the area at this point.

High pressure builds in from the northwest Friday, with potential
MVFR ceilings at KBLF/KLWB before the high arrives. Another front
may cross through the region on Saturday with possible showers
and MVFR ceilings in the mountains. However, models were still
showing differences in the timing of the weekend system.


As of 315 AM EDT Tuesday...

Very dry conditions will continue to persist today as high
pressure builds into the region from the northwest and wedges down
east of the mountains by the middle of the week. Expect this to help
reduce winds this afternoon with speeds on average below 10 mph.
This while the flow turns more northeast across eastern sections
with variable to light westerly trajectory across the mountains
through the afternoon. Temperatures will also be cooler but given
the arrival of even drier air behind a cold front from Monday,
appears afternoon humidity levels will fall to between 20 and 30
percent across much of the region. Therefore will continue to
headline the fire weather forecast (FWF) for low humidity levels
today. Humidity may recover a little on Wednesday ahead of an
approaching cold front. This front should bring the next round of
scattered showers Thursday although the chances for widespread
wetting rainfall appear low at this point. Dry air returns again
for the end of the week behind the front.


VA...Frost Advisory until 9 AM EDT this morning for VAZ007-009-010-
WV...Frost Advisory until 9 AM EDT this morning for WVZ042>044-507-


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