Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 161747

Area Forecast Discussion
National Weather Service Blacksburg VA
147 PM EDT Sun Jul 16 2017

A weak frontal boundary across northern North Carolina will
drift further south today, then return slowly north Monday.
Meanwhile, a weak upper trough will develop across the eastern
U.S. and drift slowly east through midweek. Strong high pressure
aloft from the Midwest will build eastward during the later half
of the week.


As of 146 PM EDT Sunday...No significant changes made to the
early-afternoon forecast update, though did opt to adjust
dewpoints some through the rest of the day. Relatively sharp
moisture gradient across the forecast area early this afternoon,
with drier dewpoints (50s to around 60 common) along and west
of the Blue Ridge, contrasting with dewpoints about 10 degrees
higher across the NC foothills, VA/NC Piedmont and Southside.
With dry air aloft, should see some lowering as boundary layer
deepens but still somewhat more humid across these southeastern
sections. Otherwise, looking at some diurnal fair weather
cumulus dotting the mountains. Overall a great afternoon for
outdoor activities.

Previous near-term discussion issued at 400 AM follows...

Latest LAPS analysis shows the dewpoint/frontal boundary is
roughly along a line from CLT to RDU, north of which dewpoints
fall into the 60s, yet south of which dewpoints are still in
the lower to mid 70s. West of the Blue Ridge, dewpoints have
dropped into the 50s across the mountains allowing for a cool
morning with locations such as LWB and BCB seeing temperature in
the 50s early this morning, extremely pleasant for mid-July
when much of the country is suffering with heat and humidity.

Expecting a dry day today with none of the normal summer convection
as the dewpoint boundary continues to drift further south
toward the NC/SC border leaving a stable air mass in place
across the region, much as we saw Saturday, drier even further
south today. Several models hint at least some period of mid
clouds developing southwest into the area from central VA and
possible also advecting into the southeast parts of the CWA
early in the day. Another potential minor concern from an
otherwise precipitation free period is a disturbance in
northwest flow tracking just north of the area late in the
day/evening, which could bring scattered showers/thunderstorms
to the northern Alleghanys of WV, clipping northern Greenbrier
county. Have hinted at this with a 15-20% pop in those areas
late afternoon/early evening. Don`t want to go any higher at
this point given the lack of deep moisture present.

Otherwise, basically a temperature forecast. 850mb temperatures
still hovering near +20C through the period, so even with the
forecast area being behind the front, with these temps aloft in
place and strong July sunshine, look for highs to still reach
well into the 80s west to near 90 across the Piedmont. With the
lower humidity, it will feel somewhat less hot, even in the
Piedmont today.

Overnight, moisture begins to return to the southeast part of
the CWA in particular as a broad upper trough develops across
the eastern U.S. Western, higher elevation terrain will retain
the drier air through Monday morning. The net effect of all of
this will be that low temperatures Monday morning are expected
to be on part with this mornings lows, namely mid to upper 50s
high elevations and mountain valleys west to mid and upper 60s


As of 430 AM EDT Sunday...

As a stalled frontal boundary remains to our south over the South
Carolina coast, an upper level trough will approach from the Great
Lakes. This situation puts our CWA in the middle between these
systems on Monday. As a result, all the models are trending downward
with rainfall chances during the afternoon, so POPS were lowered
somewhat to account for it. The southern Blue Ridge and parts of
southeast West Virginia still could fire scattered showers and
thunderstorms from typical diurnal and orographical effects.

The upper level trough should pass overhead by Monday night, and
push the stubborn frontal boundary offshore. As this trough lifts
northeastward during Tuesday, the GFS and ECMWF models have come
into better agreement with the large 597 dam ridge over the Plains
beginning to nose eastward toward the Mid Atlantic. Look for the
heat to crank up more toward the end of this period. Shower and
thunderstorm activity appears more isolated in coverage for the
afternoons of Tuesday and Wednesday, so just slight chance to low
chance POPs were kept in place.


As of 430 AM EDT Sunday...

The latest model solutions have turned more progressive with the
upper level trough heading offshore. Thus, the large 597 dm
upper level ridge should continue to push toward the Mid
Atlantic. Expect hot and humid conditions later in the week. As
the flow turns more northwesterly aloft by Friday and Saturday,
there is the potential for scattered thunderstorms to develop
from mesoscale convective systems upstream and propagate toward
our CWA, but there are still lots of questions that need
answered before any confidence on this situation can be
obtained. For that reason, this forecast will stay closer to the
blended solutions to minimize errors.


As of 146 PM EDT Sunday...VFR through the afternoon and early
evening with FEW-SCT fair wx cumulus clouds. Looking at
generally clear and calm conditions tonight with development of
patchy IFR/LIFR fog mainly after 08z. Best chances at Lewisburg
and Blacksburg along the Greenbrier and New Rivers, though
should also see a potential for IFR visibility at Roanoke,
Lynchburg and Danville as low-level air mass moistens overnight
along and east of the Blue Ridge. Light winds (tending northeast
in the Piedmont and light northwest along/west of the
mountains) this afternoon becoming light to calm.

For Monday, any overnight fog should burn off readily with
sunshine today. Expect to see deepening cumulus field with bases
around 060. Scattered showers and thunderstorms anticipated to
develop near the Blue Ridge spine, a couple which may pose a
gusty wind threat. Indicated VCTS at Blacksburg, Roanoke and
Lewisburg at 17z due to timing uncertainties, though greater
storm coverage after this 18z TAF issuance. Potential also
should exist in the southern Blue Ridge for flight routes
through the southern mountains. Localized turbulence due to
erratic outflow gusts, brief visibility reduction and lightning
all potential hazards in thunderstorms, though better chance
after this TAF issuance. Winds through Monday afternoon
generally light southeast east of the Blue Ridge, more of a
light west to west- southwest for Bluefield.

Aviation Extended Discussion...

Greater thunderstorm coverage and their associated lightning,
outflow wind and IFR visibility risks expected Monday late
afternoon into early evening near the Blue Ridge. More limited
potential east of the Blue Ridge into the Piedmont. A few may be
on the strong side during the mid to late afternoon. Storms
should begin to diminish in coverage and strength with sunset
with VFR conditions anticipated Monday night.

VFR conditions with isolated thunderstorms Tuesday confined to
the daylight hours and the mountains. VFR dry weather expected
Wednesday before threat of scattered thunderstorms increases
again for mid to late in the week. Potential for nighttime IFR
to LIFR radiation fog increases each evening during this period
as moisture levels increase.




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