Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 230931

Area Forecast Discussion
National Weather Service Blacksburg VA
431 AM EST Thu Feb 23 2017

Weak high pressure off the Mid Atlantic coast will cover
Virginia and North Carolina today and tonight. A front across
the Great Lakes into the southern Plains shifts slowly southeast
to the Ohio Valley by Friday. The main cold front approaching
from the Midwest will pass through our area Saturday.


As of 430 AM EST Thursday...

No changes planned to Dense Fog Advisory. Numerous locations
reported visibility of one half mile or less. The few exceptions
were on the western slopes from Bluefield to the Mountain
Empire area and along the peaks of the Blue Ridge which were
higher than the depth of the fog.

Models showed a modest improvement in visibility after 10AM. A
few breaks in the clouds are possible from Charlotte County
Virginia to Yadkin County North Carolina late this afternoon.
With little to no heating today...temperatures rise will be
limited. Have trimmed maximum temperatures today and may still
need them lower depending on cloud cover.

Some isentropic lift forecast today from Kentucky into western
Pennsylvania. Otherwise little forcing so have lowered
probability of precipitation.

Bufkit forecast soundings and visibility guidance showed
reformation of fog again late tonight. Have added larger
coverage of fog after midnight.


As of 300 AM EST Thursday...

Weak shortwave ridging will build over our area Friday, as a mid-
level trough/low is forecast to move into the Great lakes and Ohio
Valley. It will remain unseasonably mild and generally rain free.
The only exception is a few locations near the crest of the Blue
Ridge thanks to local upslope flow. trimmed back pops a little
friday and shaped towards the NAM. High temperatures Friday
afternoon will range from the lower 60s in the mountains to the mid
70s in the Piedmont.

A cold front will approach the region from the west Friday night and
reach the mountains Saturday morning. Showers and a few
thunderstorms will develop along and ahead of the cold front. The
Day two convective outlook brings general thunderstorms into western
portions of the forecast area. The marginal threat clips a few far
western counties. It still looks like the best instability will
remain north of the Ohio River. Low temperatures Friday night into
saturday morning will vary from the mid 40s in the northwest
mountains to the the 50s in the Piedmont.

A cold front will move east across our area Saturday with scattered
showers and thunderstorms. The mention of thunderstorms remains
support by the sfc best lifted index and computed cape values.
The latest SWODY3 places portions of cwa in a 5 percent chance of
severe weather, Marginal threat. The main threat is for convective
lines with damaging winds. High temperatures on Saturday will warm
to the mid 50s in the mountains to the lower 70s in the Piedmont.

By Saturday night, the front will be to our east, and northwest
winds will be on the increase. The northwest winds will yield some
gusts approaching 40 to 45 mph at the highest elevations. At this
time, it appears that winds will remain below wind advisory levels.
With colder air pushing into our region, any lingering upslope rain
showers across parts of southeast West Virginia, south into the
northern mountains of North Carolina are expected to transition
to snow showers by Sunday morning. Little or no accumulations
expected with any snow showers. Low temperatures Saturday night
will be near normal with readings from the lower 20s in the
mountains to the mid 30s in the Piedmont.


As of 300 AM EST Wednesday...

Gusty winds will continue into early Sunday behind Saturday`s cold
frontal passage. These winds will weaken quickly during the day and
back southwest as the next upper level trough deepens across the
Central Plains.

This same upper trough will move east and be over the Ohio Valley by
mid-day Monday. A warm front in advance of this system will head
north through our region, bringing a return of patchy light
precipitation to the area during the day Monday. There may be an
issue of a brief period of a wintry mix across the northwest section
of the area early Monday as a potential warm nose develops over a
sub-freezing boundary layer and surface. For now, will keep things
simple by reflecting a rain versus snow forecast based solely on
whether the forecast surface temperatures is above or below

Monday night the system`s associated cold front is expected to cross
the area. Look for the precipitation to become more showery Monday
night into early Tuesday.

Model guidance for the remainder of Tuesday into Tuesday evening is
not clear. The GFS is progressive with the cold front making
significant headway east of the region. The ECMWF is not
progressive, stalling the feature over the area, all while
suggesting another wave will move northeast along this boundary,
keeping a generous coverage of rain across the area Tuesday
afternoon into Tuesday night. Our forecast will reflect a blend of
these solutions. While rain will be forecast Tuesday afternoon and
evening, it will not be to the degree offered by the ECMWF.

For late Tuesday night into Wednesday, model agreement improves with
solutions bringing yet another upper low/trough from the Central
Plains states into the Ohio Valley. Warm frontal rain is expected
late Tuesday night into early Wednesday, with a generous coverage of
showers and some isolated thunderstorms across the area Wednesday
afternoon coincident to the cold frontal passage. Behind the cold
front in the northwest flow, a few rain and snow showers may linger
in the western mountains Thursday.

Temperatures Sunday and Monday will be normal for this time of year.
Reading moderate through mid-week with temperatures some ten to
fifteen degrees above normal expected.


As of 1030 PM EST Wednesday...

Dense fog advisory along and just east of the Blue Ridge through
10am Thursday. In spite of clearing aloft, a very moist
boundary layer with RH values of 100% has allowed for the
formation of dense fog with widespread visibilities under 1/2SM
Lack of wind will allow this fog to persist through mid-morning
Thursday before daytime heating begins to mix the boundary layer
and allow for improvement. Until then expect Widespread LIFR.
This is a situation where the valleys and lowland areas will
contain more stratus and fog as compared to the ridges. Ridge
tops will likely remain above the stratus layer.

The fog/stratus looks to burn off Thursday morning with a
return to VFR conditions by the afternoon. However, a weak
frontal boundary will brush the region as an area of low
pressure moves through the Great Lakes region tomorrow. This may
bring a shower to locations west of the Blue Ridge so will
include VCSH after 18Z all sites except KDAN and KLYH. Winds
will be light through the period.

Extended Aviation Discussion...

Thursday night-Friday, we will be well into the warm sector
with VFR conditions and much above normal temperatures. Surface
wind gusts of 20 to 30 kts possible across the higher terrain.

Band of showers and isolated thunderstorms with MVFR conditions arrive
late Friday night into early Saturday along and ahead of a
strong cold front. Drier weather and increasing northwest winds
follow behind the front on Saturday afternoon through Sunday.

Approach of another front Monday will provide increasing clouds
and possibly showers and MVFR cigs to BLF/LWB late in the day.


As of 245 PM EST Wednesday...

Warm temperatures set to occur again Thursday with increase in
westerly flow in the low levels. Question will be cloud cover. At
the moment with some sunshine look for highs and lows to approach or
break records for Feb 23rd.

Thursday 02/23/2017
Site        Record High/Year  Record Warm Low/Year
Bluefield       74 1975          51 1975
Danville        73 1980          50 1981
Lynchburg       74 1943          52 1925
Roanoke         76 1943          54 1925
Blacksburg      69 1980          46 1990


VA...Dense Fog Advisory until 10 AM EST this morning for VAZ007-
NC...Dense Fog Advisory until 10 AM EST this morning for NCZ001>006-
WV...Dense Fog Advisory until 10 AM EST this morning for WVZ042>044-


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