Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Remove Highlighting --
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FXUS61 KRNK 201407
Area Forecast Discussion
National Weather Service Blacksburg VA
1007 AM EDT Sat Aug 20 2016
Weak high pressure will slide across the region today into
tonight keeping warm and humid conditions in place. A strong cold
front will approach from the west late tonight before crossing the
area Sunday. Somewhat cooler and drier air follows the front for
much of next week.
.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --As of 1007 AM EDT Saturday...
Pockets of low clouds and fog are slowly mixing out this morning.
The low clouds and fog will burn off or lift by late morning,
returning sunshine for this afternoon. The combination of low
level moisture and instability will generate scattered showers and
thunderstorms this afternoon into this evening. The best chances
of convection will occur across the southwest mountains. With
pwats around 1.4 inch, any slow moving thunderstorms could produce
locally heavy rains. Adjusted temperatures with latest obs and
trend, then shaped early afternoon with lav guidance. Blended in
the HRRR for pops this morning into this afternoon.More changes
As of 240 AM EDT Saturday...
Overall rather diffuse weather scenario to continue today with dry air
aloft per vapor loop sliding in behind the departing wave from Friday
and over returning low level moisture from the southwest later on. This
in conjunction with broad zonal flow aloft but with lack of much upper
forcing given weak high pressure in place. However models agree that
low level convergence should take shape initially over the west this
afternoon along the leading edge of the higher pwats and where the
flow turns more southwest similar to a warm front aloft. This also
aided by a more southeast trajectory along/east of the Blue Ridge
as the residual low level surface trough to the south starts to
lift back northeast under weak return flow. Latest short term solutions
support this convergence maximizing near the southern Blue Ridge initially
before the axis shifts east later in the day. Progged instability
not overly impressive given possible early mid deck although decent
return of 850 mb theta-e ridging mountains likely enough to pop a
few clusters/bands of slow moving convection given weak flow aloft.
Therefore going with a small window of low likely pops southwest
sections this afternoon with chance pops gradually spreading in from
the southwest as the belt of deeper moisture lifts east/northeast.
Could easily see northeast sections again go basically dry where
the weak residual wedge may hang on so lowest pops there as expect
guidance again overdone. Exodus of mid clouds this morning along
with warming aloft should push high temps back into the upper
70s/low 80s west and mid/upper 80s east.
Expect any evening convection to basically fade by midnight given lack
of support and loss of heating before lift associated with the upstream
pre-frontal band of convection approaches late. Rapid movement of this
weakening convective band well ahead of the actual cold front likely to
be near the far western counties by daybreak if it holds together. Thus
after cutting pops back after this evening, ramping back up to high
chance/likelys western slopes late per latest GFS/EC, with little east
of the Blue Ridge. Otherwise partly cloudy early with more clouds west
by dawn including patchy fog again valleys and out east. Expect a
little more mixing west ahead of the front to hold lows up in the 65-70
range with mainly low 70s east.
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.SHORT TERM /SUNDAY THROUGH TUESDAY/...
As of 300 AM EDT Saturday...
A strong cold front will move over the region Sunday. This front
will remove dewpoints in the upper 60s to lower 70s and replace them
with 50s. Even though this is an impressive front, convection
activity will be some what lacking, mainly due to weak dynamics and
showers coming across the area during the morning and early
Showers are expected to be along the western slopes of SW VA/SE WV
by sunrise, then to the Blue Ridge by noon. There should be a wide
area of rain as the front moves over the mountains. Winds quickly
become westerly following the front which could limit areal coverage
east of the Blue Ridge. A rain shadow may occur over the foothills
with a secondary line forming across Southside during the afternoon
(NAM solution). However, the front slows its eastward progress as it
approaches the Blue Ridge. Winds will be able to back long enough to
carry and maintain showers across the foothills and piedmont
counties during the afternoon.
Instabilities not overly impressive, therefore will have scattered
thunderstorms instead of thunderstorms likely. Can not rule out a
strong thunderstorm or two towards Southside, especially if clear
skies are maintained through much of the morning. Models,
particularly the NAM, displaying strong convection developing east
of Route 15 (Kerr Reservoir-Occoneechee State Park). Showers will
end quickly from west to east through the afternoon, exiting the
piedmont by sunset.
Temperatures and dewpoints will dramatically fall as the rain and
front moves east. Monday and Tuesday afternoon highs will be below
normal, ranging from the mid 70s to lower 80s. Relative humidity
each afternoon will be at or below 50 percent. The coolest air
arrives Monday night with lows dipping into the low to mid 50s.
.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
As of 245 PM EDT Friday...
High pressure will remain over our region through at least Wednesday
of the upcoming week. By Thursday, the center of the high will be
far enough east for western portions of the area to see a return of
isolated to scattered showers and a few thunderstorms. By Friday,
guidance currently offers a solution of a cold front moving into the
Ohio and Tennessee Valleys. Anticipate an increase in showers and
storms across most of the forecast area. Only the far eastern part
of the area may miss out on the activity.
Temperatures during the early part of this portion of the forecast
will be at or slightly below normal. Thursday into Friday
temperatures will be increasing again so that they will be around
.AVIATION /14Z SATURDAY THROUGH WEDNESDAY/...
As of 655 AM EDT Saturday...
Varied conditions from IFR/LIFR in the valleys and eastern low
spots to MVFR or VFR will continue early this morning given range
from dense fog/stratus to only mid deck elsewhere. Expect the low
clouds/fog will burn off or lift by mid morning returning most taf
locations to VFR or high end MVFR in higher based strato- cu that
is currently just west of the region.
Weak high pressure will build into the region this morning with
deeper moisture mainly south/west of the area ahead of a strong
upstream cold front. This may only result in periods of MVFR/ocnl
IFR in isolated to scattered shra/tsra this afternoon with better
coverage holding off until this evening and over the far west with
the overnight pre- frontal showers and thunderstorms. Since
appears best chances of convection this afternoon will be from
the Blue Ridge west, limiting any vicinity mention to mostly the
mountains as expect KLYH to remain dry until late in the day or
A second round of showers and thunderstorms including possible
MVFR/IFR may take place late tonight with the pre- frontal band
of convection ahead of an approaching strong cold front. This
could tend to limit fog formation given cloud cover and mixing.
Otherwise VFR outside of any added showers until late tonight
when will include some sub-VFR in most locations due to fog and/or
Extended aviation discussion...
A secondary band of showers and thunderstorms including MVFR/IFR
will take place Sunday along a strong cold front that will pass
through the region by Sunday night. Much drier air is anticipated
after Sundays frontal passage with a dry forecast for Monday
through Wednesday promoting VFR for much of the Mid- Atlantic. By
Thursday, the center of the high will be far enough east for
western portions of the area to see a return of isolated to
scattered MVFR showers and a few thunderstorms.