Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Highlight Changed Discussion --
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FXUS61 KRNK 230531
Area Forecast Discussion
National Weather Service Blacksburg VA
131 AM EDT Fri Sep 23 2016
Low pressure along the coast of South Carolina slides slowly north
along a front through Friday with high pressure shifting over the
Southern Appalachians. A backdoor cold front will approach from the
north Friday into Saturday, then slide south across the region
Saturday night. Canadian high pressure will move across southeast
Canada and wedge down the east side of the appalachians starting
.NEAR TERM /THROUGH TODAY/...
As of 320 PM EDT Thursday...
Low pressure along the coastal boundary will slide north tonight
into Friday. Meanwhile, the upper low weakens and opens up into
Friday. At the same time, a cold front will approach us from the
north. Northeast flow transporting moisture this afternoon into
tonight resulting in clouds with isolated to scattered showers this
afternoon into tonight mainly east of the Blue Ridge mountains. For
tonight expecting showers to taper off or diminish with clear skies
in the northwest to cloudy skies in the southeast. With less mixing
and clear skies, patchy fog will form in the river valleys. Low
temperatures tonight will range from the mid 50s in the northwest
mountains to the mid 60s in the Piedmont. The upper low continues
filling along the Carolina coast on Friday. With decreasing upper
level support and shallower moisture, final expect the column to dry
out for Friday. High temperatures on Friday will vary from the mid
70s in the mountains to the mid 80s in the Piedmont.
.SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/...
As of 320 PM EDT Friday...
The upper level low that has hovered over the southeastern US for
the last several days will get pushed out to sea Friday night and
Saturday. This will allow a back door cold front to slide south
across the region Saturday night. Surface high pressure will then
move across southeastern Canada and wedge down the east side of the
Appalachians through Sunday. Even though the surface wedge boundary
moves over the Carolinas, the associated theta-e boundary will stall
across northern Virginia. With ample low level moisture and
isentropic lift, gray and damp conditions are likely with light
rain/drizzle, low clouds and fog Sunday and Sunday night.
Temperatures will be a nightmare to forecast especially if the
backdoor front is slow to move south Saturday night. Also, if the
theta-e boundary is able to move farther south Sunday, less rain and
clouds can be expected which could lead to warmer than forecasted
temperatures Sunday. For this package, we will undercut guidance by
3F-6F based on Cold Air Damming (CAD) climatology for areas along
and east of the Blue Ridge and close to normal in the Bluefield-
Richlands area who will be on the fringe of the wedge.
.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 300 PM EDT Friday...
Upper level ridging across the east will make for slow progress with
regards to any significant weather changes through the period. The
wedge that will be in place on Sunday will erode some over the
mountains, but hangs on east of the Blue Ridge into Monday night. An
upper level low over the Great Lakes will slowly push a cold front
into the region Wednesday, then the front stalls just east of the
Blue Ridge. With a blocking pattern in place and the upper low
becomes cutoff from the steering flow per the 12Z GFS, the second
half of the week could be very wet for the region. The Euro also
stalls the next front over the area Wednesday but is booted to the
east by Thursday. Needless to say, there is very little confidence
in next week`s forecast.
.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --As of 125 AM EDT Friday...
Just a few showers near DAN early this morning so kept VCSH in for
another few hours. Looks like DAN will be the only site with MVFR
conditions this morning in terms of ceilings. Given how dry it has
been, fog has not be an issue, however with cooler temperatures,
may see some radiation fog at BCB/LWB but not going any worse than
2sm. Confidence is not high on this, as with these sites it
usually runs either P6sm or < 1sm.
Friday during the day will be seeing clearing with Danville coming
to VFR by 16z. High pressure will keep it VFR til the end of this
taf period with deeper moisture staying southeast of our forecast
Extended aviation discussion...
VFR conditions will prevail through Saturday with high pressure in
place. A back door front passes across late in the weekend into
early next week which may bring sub VFR ceilings as an easterly
flow sets up. These MVFR or lower ceilings may stay in place
through Monday. Rainfall chances will stay low however, though
some upslope component from the southeast could bring showers/rain
to along the Blue Ridge south of Roanoke/Blacksburg Monday.
A strong, but slow moving, cold front will be approaching the
area from the west on Tuesday. Models have significant differences
on the timing and location of this front.
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