Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 270821

Area Forecast Discussion
National Weather Service Blacksburg VA
421 AM 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.


As of 330 AM EDT Tuesday...

A slow moving cold front will make it to the Blue Ridge by sunrise
this morning, then slowly work across the foothills and stall over
the piedmont this afternoon. Heavy rain will accompany the front
this morning, then intensity of these showers will lessen moving
into a worked-over environment across the foothills and piedmont
counties. 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.


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.


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.


As of 120 AM EDT Tuesday...

Generally poor aviation conditions expected through this morning.
A cold front was moving across the mountains early this morning
with a broken line of showers. Ahead of the front are some
prefrontal showers across Southside (KDAN), but mostly MVFR-IFR
low clouds and fog from the Blue Ridge eastward.

For the TAF valid hours after 14Z Tuesday, look for variable
clouds as an upper low begins to drift southward from the Great
Lakes region. Ceilings will range from high end MVFR or low end
VFR by afternoon. Showers remain possible across the Piedmont,
including Danville, as a wave of surface low pressure rides
northeast along the slow moving frontal boundary located over the
coastal plain.

Extended aviation discussion...

The front will be located across the coastal plain into Wednesday
awaiting additional upper support from an approaching upper low.
Conditions will becoming increasingly unsettled as a deep upper
low sags southward from the Great Lakes into the Central
Appalachians. This will keep variable clouds, MVFR cigs, and
periods of -SHRA across the region through much of the period.




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