Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Highlight Changed Discussion --
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FXUS61 KRNK 271737
Area Forecast Discussion
National Weather Service Blacksburg VA
137 PM EDT Tue Sep 27 2016
A cold front will move east of the Blue ridge this morning, then
stall over the piedmont this afternoon. A wave of low pressure
moving along this front will keep the chance for showers across
foothills and piedmont counties on Wednesday, before finally
exiting Wednesday night.
.NEAR TERM /THROUGH TONIGHT/...
As of 1020 AM EDT Tuesday...
A cold front had advanced to the east side of the Blue Ridge as
of 10AM. Lower dew points, in the mid 50s, had reached the border
between West Virginia and Virginia. Have trimmed back the
Probability of precipitation west of the Blue Ridge, in locations
behind the front.
Instabilities will increase some across Southside this afternoon,
as a weak short wave tracks along the front across central North
Carolina. A closed upper level low will track from the Great Lakes
today to the Ohio Valley tonight. As this low sinks south, the
front and its showers will get pushed to the east.
Temperatures will be close to seasonal averages ranging from the
low to mid 70s west to mid to upper 70s east.
.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 400 AM EDT Tuesday...
By early Wednesday, an upper low situated across the corn belt is
expected to begin meandering south and east toward the northwest
portions of our forecast area. Around the same time, a short wave is
expected to ride the residual frontal boundary just to our east,
reinvigorating the fetch of deep moisture. Scattered showers with
potentially a rumble of thunder should remain east of the Blue Ridge
Mountains through Wednesday evening as the low begins to dig further
south. An isolated shower will be possible across the western slopes
of the Appalachians just after sunset.
At this point, solutions begin to differ rather greatly. The latest
few model runs continue a moistening trend, with the ECMWF leading
the pack. The bulk of the precip tends to stay north and east of
the forecast area for now, but have once again introduced higher
POPS out east out of respect to the very wet ECMWF which seems to
emphasize the short-waves effect rather stoutly. Have re-
introduced thunder into the forecast for the same portion of the
forecast area Thursday, as impressive low to mid level lapse
rates look to combine with very low freezing heights across the
area. This should allow for a small hail threat to develop, even
in an environment only favorable for shallow-type convection.
Heavy rain in the showers/storms that do form will be the main
Temperatures during this portion of the forecast will remain at or
below normal, limited greatly by cloud cover and rapid cold air
advection around the low pressure system.
.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 130 PM EDT Monday...
The slow moving upper low will continue to impact our forecast into
Friday, however, the trend will be for the low to start heading
north in response to a building upper ridge across the center
portion of the nation. Progressively each day through Sunday, the
concentration of showers will will trend more toward the northern
sections of the forecast area, following the track of the low. While
no thunderstorms are forecast, isolated hail will again be possible
within the stronger showers given a continuation of a relatively low
freezing level through Saturday.
Sunday into Monday, a dry forecast is expected along with moderating
temperatures as the upper ridge strengthens and its axis shifts
eastward. At best some isolated showers may be possible across the
Northern Mountains of North Carolina on Monday where
Temperatures during this portion of the forecast will trend only
slightly milder on average than the early part of the week. While
highs may climb a bit higher, lows are expected to trend slightly
cooler as the diurnal range increases thanks to decreasing dew point
values across the region.
.AVIATION /17Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --As of 120 PM EDT Tuesday...
A front extended from central Virginia to western North Carolina
this afternoon. There will be little movement of the front tonight
Showers and thunderstorms will develop this afternoon east of the
front, with the best probability of precipitation at KLYH and
KDAN. Medium to high confidence that the showers and thunderstorms
will form around 21Z/5PM. Gusty winds are possible with any of
the stronger storms but the chance is too low at any individual
TAF site to include in the forecast at this time.
Models, especially the NAM, showed IFR to LIFR ceilings east of
the front overnight. High confidence that KLYH will have LIFR
ceilings after midnight. LIFR ceilings are possible at KDAN too
but confidence was too low to include in the forecast. Over the
mountains with little cloud cover, fog will form in the river
valleys. Expect LIFR fog and stratus at KLWB after 2AM. Low
confidence about how long it will take the low clouds in the
foothills and piedmont of Virginia and North Carolina to lift
Extended aviation discussion...
A deep upper low will remain over the Ohio and Tennessee Valley
through Friday. This will keep variable clouds, MVFR cigs, and
periods of -SHRA across the region through much of the period.
Saturday is the most likely day to be drier and have VFR
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