Area Forecast Discussion
Issued by NWS Wakefield, VA

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FXUS61 KAKQ 280814
AFDAKQ

Area Forecast Discussion
National Weather Service Wakefield VA
414 AM EDT Wed Sep 28 2016

.SYNOPSIS...
Low pressure tracks north across the North Carolina and Virginia
piedmont this afternoon and tonight. An upper level low slowly
drops south from the Great Lakes region resulting in unsettled
weather conditions into the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Latest GOES water vapor imagery centers a deep/anomalous upper
low over the western Great Lakes region with a plume of high water
vapor lifting into the Mid-Atlantic region. At the surface, a weak
quasi-stationary boundary has located over the forecast area.
Scattered showers over the Piedmont will continue to lift along
the boundary into central Virginia through daybreak as weak
shortwave energy lifts across the region. Areas of fog will also
linger through early morning across central Virginia, before
lifting/eroding by mid morning.

The upper low drops southward today, centering over Indiana late
today. Associated surface low drops over the Ohio Valley.
Diffluent flow over the local area and increasing winds aloft will
provide strong forcing for ascent along the stalled frontal
boundary. Deep layer southwesterly flow will advect anomalous
precipitable water values into the region. Scattered to numerous
showers expected to develop early afternoon as the better forcing
arrives, and persist through the day and into the overnight
period. Have increased POPs across the area to high end likely and
categorical. Theta-e advection and dewpoints in the mid to upper
60`s will result in marginal instability. Deep layer shear progged
on the order of 30-35 knots, resulting in a chance of
thunderstorms. Gusty winds are possible, but the main impact will
be locally heavy rainfall in thunderstorms that develop. Highs
range from the mid 70`s northwest to low 80`s southeast.

The upper low slowly drifts southward tonight as another area of
surface low pressure approaches from the northwest. Height falls
over the region progged to develop a wave of low pressure along
the frontal boundary tonight, with an area of strong isentropic
lift across the Piedmont to the Maryland Eastern Shore. The result
will be ongoing categorical POP`s and the potential for moderate
to locally heavy rainfall. Lows forecast in the mid to upper 60`s
under a cloudy sky.

Rainfall totals through the near term expected to range from 1-2
inches across the Piedmont and central Virginia to one quarter to
one half inch northeast North Carolina.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY/...
Anomalous upper-level low centers over Kentucky Thursday, with
deep layer southerly flow over the Mid-Atlantic. At the surface,
an associated area of low pressure and attendant cold front drop
into north central North Carolina. High pressure located over the
Northeast will help keep low pressure south of the region, with
onshore flow north of North Carolina. Deepest moisture and
theta-e/instability axis begin to pivot northward, but showers
with embedded thunder persist. Best coverage and heaviest
precipitation forecast Richmond northward through the day,
tapering off to solid chance POPs far southern Virginia and
northeast North Carolina late Thursday. Highs Thursday range from
the mid 70`s northwest to low 80`s southeast. The upper low moves
very little Thursday night as a frontal boundary pivots northward
from North Carolina, locating over the forecast area. By that
time, the deepest moisture progged to be north of the region, but
precipitable waters around 1.5 inches and strong upper level
dynamics will keep solid chance to likely POPs in the forecast.
Lows in the mid to upper 60`s.

Forecast has trended wetter and cloudier Friday than 12 hours ago
as the stubborn upper low remains centered in the vicinity of
eastern Kentucky. Deep layer southerly flow prevails, but the
deepest moisture continues to pivot north and east of the region.
Strongest onshore moisture flux progged north of the region,
keeping the heaviest rain away from the local area. However, the
combination of continued upper vertical motion and the presence of
the frontal boundary will keep solid chance to likely POPs across
the region through the day Friday. Sky remains mostly cloudy to
cloudy. Highs forecast in the mid 70`s northwest to low 80`s
southeast.

Per SREF and GEFS mean guidance, storm total rainfall amounts
expected to range from 3-4 inches north and west of Richmond to
around one half inch in northeast North Carolina. Rainfall amounts
generally 1-3 inches elsewhere. No flood watch products issued on
this shift as the anomalous flow remains north of the region.
However, localized minor flooding from several periods of showers
(some heavy at times) is possible.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Long term period starts off Fri night/Sat with an upper-level cutoff
low and associated sfc low centered over the OH Valley. Better rain
chances will stay north of the area, but included at least a 20-30%
chance of showers especially over ne areas where the highest
moisture will be located. Mainly dry conditions thereafter into Sun
and Mon as the cutoff low weakens and slides ne into Canada. As for
temps, highs will generally be in the mid/upper 70s with lows
ranging from the mid/upper 50s over the Piedmont to the mid/upper
60s near the coast.

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
Widespread IFR conditions observed across central Virginia early this
morning with visibilities as low as 1/2 mile and ceilings down to
around 300-1200 feet. The exceptions are the Maryland Eastern
Shore and southeast Virginia/northeast North Carolina where
MVFR/VFR conditions are observed. Expect poor aviation conditions
from the Piedmont into central Virginia through mid morning
before improvement. Visibilities could drop to airport minimums at
times at KRIC and KPHF. MVFR conditions KSBY. Scattered showers
and embedded thunderstorms lifting over the Piedmont will spread
northeastward, possibly reaching central Virginia around daybreak.
Winds generally at or below 10 knots.

The weak boundary remains over the region today as an upper level
disturbance drops into the region. Expect another round of
widespread showers and embedded thunderstorms to develop late
morning through the afternoon, spreading northeast through the
day. Lower chances southeast Virginia/northeast North Carolina.
MVFR conditions expected.

Outlook: Unsettled weather conditions expected through the end
of the work week as waves of low pressure lift along the cold
front. Showers with late day thunderstorms will be possible each
day.

&&

.MARINE...
Latest analysis shows a broad area of surface low pressure over the region,
with another area of low off the coast. Strong/anomalous surface high
pressure is situated over eastern Canada. The pattern over the next few
days will feature this strong high building over eastern Canada, ridging
into New England and the northern mid-Atlc region. This will make for
a persistent and rather strong E/NE flow over northern portions of the
marine area. Have added Bay zones N of New Pt Comfort to the SCA as well
as the coastal waters from Cape Charles to Parramore Island (beginning
late tonight or Thu morning). Seas are expected to build to 6-8 ft over
northern waters, while remaining around 4 ft across the south). It is
possible that marginal SCA conditions could make it to NC border for
5 ft seas by Thu aftn and that lower Bay could also get to marginal
SCA levels (but confidence is rather low at this occurring and given
that it would be 3rd period did not go that far with the headlines).

Seas will slowly subside Fri-Sat (though the headlines will likely need
to be extended through at least Fri night eventually).  A lighter
SSE flow expected Sat leading to sub-SCA conditions with 1-2 ft waves
over the Bay and 2-4 ft seas over coastal waters.

&&

.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...None.
NC...None.
VA...None.
MARINE...Small Craft Advisory from 7 AM Thursday to 6 AM EDT Friday for
     ANZ654.
     Small Craft Advisory from 7 PM this evening to 6 AM EDT Friday
     for ANZ650-652.
     Small Craft Advisory from 7 AM Thursday to 1 AM EDT Friday for
     ANZ630-631.

&&

$$
SYNOPSIS...SAM
NEAR TERM...SAM
SHORT TERM...SAM
LONG TERM...MAS
AVIATION...AJB/SAM
MARINE...LKB


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