Area Forecast Discussion
Issued by NWS Wakefield, VA

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FXUS61 KAKQ 061203

Area Forecast Discussion
National Weather Service Wakefield VA
703 AM EST Tue Dec 6 2016

Low pressure lifts along the Southeast and Mid-Atlantic coasts
today, bringing widespread rainfall to the region. Low pressure
pushes offshore tonight as high pressure briefly returns
Wednesday. A potent cold front pushes across the region Thursday.
Arctic high pressure builds in Friday and Saturday, accompanied by
the coldest temperatures so far this season.


Latest GOES water vapor imagery depicts mid level low pressure
lifting from the Southern Plains into the lower Mississippi River
Valley, with a plume of moisture stretching from the eastern Gulf
of Mexico northeastward into the Mid-Atlantic states. Meanwhile,
an upper level ridge stretches from the local area northwestward
over the Great Lakes. At the surface, high pressure centered over
the Northeast is ridging southward over the local area as a
coastal front remains along the Southeast coast.

Upper/surface high pressure has kept the brunt of the
precipitation at bay this morning, with only light rain being
reported over the southwest Piedmont. Expect this trend to change
as the upper low de-amplifies and lifts into the Deep South and
the ridge axis pushes offshore. Deep layer southwest flow will
advect anomalous precipitable water values into the region (+200%
based on latest blended total precipitable water product). Add in
a departing 170+ kt exiting jet streak with the height falls ahead
of the upper low and forcing for ascent will be quite impressive,
especially by mid to late afternoon. Expect light rain to spread
northeast into central Virginia by daybreak as isentropic lift/WAA
overspreads the region. Low pressure develops along the coastal
front as another area of low pressure weakens over the central
Appalachians. The high retreats, as widespread rainfall spreads
over the entire region by mid to late morning. Rainfall persists
through the afternoon as the upper low finally reaches the area by
late today. Hi-res guidance indicates rainfall rates increase to
0.1 to 0.25 inches/hour this afternoon, aided by strong dynamics.
However, moisture flux remains rather meager with the best theta-e
advection remaining offshore, so any chance for locally heavy
rainfall will be tied to better forcing late today. Have increased
QPF slightly, with amounts generally ranging from around an inch
in the south to around an inch and a quarter for the Northern Neck
through today.

The upper low quickly kicks offshore this evening, with rainfall
winding down southwest to northeast. Light rain lingers for the
Maryland Eastern Shore through late tonight as wrap around
moisture from the surface low impacts the region. Soundings
indicate low levels will remain quite moist through the overnight
thanks to a northerly wind. Have increased cloud cover, especially
along and east of Interstate 95.

In-situ wedge over the region today will result in a large
temperatures spread across the local area. Daytime temperatures
across the Piedmont forecast to be lower than the current
temperatures. Thus, daytime temperatures will range from the low
40`s northwest to low 60`s southeast. Central Virginia forecast in
the mid/upper 40`s to low 50`s. Temperatures drop into the
mid/upper 30`s west to mid 40`s east tonight.


Wednesday will be a transition day as a weak secondary front
pushes across the region in fast westerly flow aloft. Low pressure
pushes well offshore as high pressure builds southward along the
Northeast coast. A dry day is in store with near seasonable
temperatures. Highs generally in the mid 50`s. Sky averages partly
cloudy as soundings indicate mid level moisture trapped under a
strong subsidence inversion. Anomalous northern stream low builds
into southeast Canada Wednesday night as the associated trough
digs into the eastern US. A strong, fast moving cold front will
reach the central Appalachians by late Wednesday night. Clouds
increase, but dry conditions expected. Lows in the mid to upper

Strong cold front quickly pushes across the forecast area Thursday
as the trough axis lags behind. Moisture will be limited with
precipitable waters at or below three quarters of an inch. While
the front is progged to outrun the best height falls, potential is
there for a narrow line of isolated to scattered showers along the
boundary. Will maintain slight chance to chance POPs, with the
best chances across the north and northeast, nearest the better
moisture. Front reaches the coast Thursday afternoon as
thicknesses inland plummet ahead of a surging arctic air mass. Any
POPs Thursday afternoon will be tied to the coast. Temperatures
warm into the upper 40`s to low/mid 50`s Thursday before
plummeting Thursday night.


Long term period starts off Thu night/Fri with dry weather behind an
offshore moving cold front. Main story in the extended will be cold
temps, with lows in the mid/upr 20s Thu night dropping to the
low/mid 20s Fri night and Sat night under continued dry weather with
sfc high pressure in the vicinity. High temps Fri and Sat avg in
the low 40s both days. Next chance of pcpn arrives Sun night/Mon
with an approaching cold front, but have capped pops for now at
20-30% with this several days out.


VFR conditions prevail early this morning, even as light rain
spreads into the region. Skies generally overcast with decks
between 6-12k feet AGL. Beginning to see MVFR/IFR conditions
spreading northward over North Carolina, but the overall model
trend has been to pull back a few hours on IFR conditions at the
TAF sites. Have indicated this in the 06/12Z TAFS, with IFR
ceiling reaching KRIC around 18Z.

Rain overspreads the region from south to northeast in earnest
between 12-15Z this morning as low pressure lifts along the coast.
Model consensus indicates MVFR conditions at onset and lowering
quickly to IFR by mid to late morning. IFR and locally LIFR
conditions are expected across the entire region by 18Z in the
form of ceilings of 400-700 feet AGL and moderate rainfall.
IFR/LIFR conditions expected to persist through the remaining 06Z
TAF issuance all sites. Northeast winds increase to around 10
knots inland and 15 to 20 knots with occasional gusts of 25 to 30
knots near the coast.

Conditions begin to slowly improve southeast to northeast late
tonight as the storm system pulls away from the region. VFR
conditions return Wednesday. A strong cold front impacts the area
on Thursday, with only a quick chance for showers Thursday
afternoon. High pressure returns Friday into the weekend.


Update:Winds have started to kick up a little sooner in the
southern waters so have started the SCA with this update at 7AM
for Currituck sound and the Chesapeake Bay. Otherwise thinking
remains the same.

Low pressure continues to deepen and lift NE through the Gulf
Coast states this morning heading toward the Ohio Valley.
Meanwhile high pressure that is along the eastern seaboard is
beginning to retreat northeastward while a coastal front is
developing along the Southeastern US Coast. Winds are currently
around 10 to 15 kt across the waters but will begin to increase
later today as the gradient tightens as the coastal front develops
and low pressure begins to form along it on the Carolina coast.
This area of low pressure will continue to strengthen this evening
as is slides of the Virginia coast and then heads eastward on
Wednesday. At this point, it appears that winds will increase to
around 15 to 25 kt on the Chesapeake Bay and 25 to 30 kt across
the coastal waters. The models show the 950 mb winds getting up to
around 40 kts, especially to the north of the low. but getting
all that winds to mix down does not look likely as lapse rates are
marginal along the coast. So have decided to drop the Gale Watch
and extend the SCA through Wednesday afternoon. There could be an
occasional gust to 35 kt between 00z and 6z Wednesday, but the
probabilities in the model are low, around 10%.

Once the low pulls off the coast, high pressure builds in on
Wednesday and should allow the winds to relax, but with seas being
slow to drop, have kept the SCA running for the coast through Wed
afternoon. They may linger into Wednesday night but for now did
not want to extend the SCA beyond Wednesday.

The next front pushes into the area on Thursday as an area of low
pressure now over the northern plains slides across the Great
Lakes and into Southern Canada. The models are differing on the
timing with the GFS and ECMWF both bring the front through early
with little moisture, while the NAM is slower and more amplified.
With the strong upper flow and cold high pressure coming behind
the front, have leaned toward the faster solution which limits any
southerly flow ahead of the front. But once the front clears, much
colder air will sweep through the waters and should produce
another round of solid small craft to near gale force conditions
into Friday night before high pressure settles over the east for
the coming weekend.


MARINE...Small Craft Advisory from 1 PM this afternoon to 1 AM EST
     Wednesday for ANZ635>638.
     Small Craft Advisory until 7 AM EST Wednesday for ANZ630>634.
     Small Craft Advisory until 4 PM EST Wednesday for ANZ650-652-
     Small Craft Advisory until 4 PM EST Wednesday for ANZ656-658.


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