Area Forecast Discussion
Issued by NWS Wakefield, VA

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FXUS61 KAKQ 041203

Area Forecast Discussion
National Weather Service Wakefield VA
703 AM EST Sun Dec 4 2016

High pressure builds across the region through today. Low
pressure passes south of the region late tonight into Monday. A
complex area of low pressure crosses the region Tuesday. A strong
cold front crosses the area Thursday.


Latest wx analysis features sfc high pressure centered over
Southern Ontario and the interior Northeast Conus, with the sfc
ridge nosing down into the Mid-Atlantic region. Aloft, closed
upper low continues to dig south across NW Mexico, with numerous
weak disturbances lifting ne toward the Gulf Coast and the Mid-
South. Weak isentropic lift is ongoing from the Mid-South into the
Western Carolinas, in the form of some spotty showers.

High pressure slides east through the morning to a position along
the Delmarva coast by mid-aftn. While this high keeps it dry in
the lower levels, top down moistening process continues throughout
the day. So while there could be some opaque sunshine early on this
morning across the east, expect the day to average out cloudy/overcast
to mostly cloudy. Isentropic lift increases by afternoon, with
the HRRR and Hi-Res models are in fairly good agreement that light
rain nudges into far SW corner of the CWA by mid to late
afternoon. Sub-Cloud Layer remains quite dry owing to the sfc
ridge, and thus only patchy light rain expected through sunset out
west, and likely holding off until this evening into the overnight
hours for most of the area. The clouds hold temps down with
thickness tools in good agreement with cooler MAV numbers. Look
for highs in the upr 40s for most to lwr 50s SE coast.

First wave of energy from the low over the deep south ejects ENE
along a developing trough over the Carolinas Sunday night. Models
agree in quickly spreading moisture NE across the fa this evening.
Best lift/support progged with southern wave over the SERN half
of the area where greatest QPF will be (1/4" n to 1/2" s). Will
carry chc e/likely pops piedmont during the evening then ramp up
to likely pops most areas, and with categorical (80-90%) across
SERN zones after midnight. light to moderate rain falling into
In-situ wedge leads to a chilly rain with lows in the upr 30s-
lwr 40s.


The sfc low pushes off the coast near Hatteras late Monday
morning, with weak ridging building south across the area
throughout the day in resultant subsidence behind the wave. Chc
pops in the morning (except likely across extreme SE zones)
quickly drop to slight chc Coastal NC zones in the afternoon, with
a dry afternoon indicated elsewhere. Low levels remain moist
enough to expect at least a partly/mostly cloudy sky through the
day (i.e. more clouds than sun). Highs warm slightly into the
low- mid 50s.

Rain begins to push back in Monday night, as a second, stronger
disturbance lifts NE through the lower Miss Valley from the
opening main upper wave across the western Gulf Coast. Isentropic
lift (290-300k sfcs) quickly ramps up again through the late evening
and overnight hours. Forcing will be much better with this second
wave, as large dry sub-cloud layer will not be as much of an
issue at this point. PW quickly ramp up AOA 1" by 12z/TUE and
1.25-1.5 across the SE. Thus rain chances ramp up quickly to
likely/categorical SW before midnight, with rain moving in over
the rest of the area after 06z/1a. Lows in the mid- upper 40s.

Tuesday`s forecast is another typical Mid-Atlantic system. Double
barreled low pressure tracks NE along the mountains with a
secondary low tracking NE along the coast. Copious amounts of both
GOM/Atlantic moisture will fall into a strong wedge across the
piedmont. Expect a wide temp range across the fa along with much
needed/widespread rainfall. Challenge will be to define where the
coastal low tracks as the NAM has an inland track with both the
GFS/ECMWF tracking the low right along the coast. For now, will
keep all pcpn stratiform with categorical pops. QPF through
Tuesday night btwn 1/2 to 3/4 inches. Temps tricky but will
continue with a sharp thermal gradient. Highs from mid-upper 40s
across the wedged piedmont to near 60 across SE coastal zones.
QPF through Tuesday night between 0.75"-1" north to 1.25-1.5"
across the SE corner of the area.

Low pulls away to begin the day Wednesday. Deep layered SW flow
should allow for clearing and a warmer day. Highs mid to upper


An upper low tracks across the Great Lakes Thursday and into
southeast Canada Friday, as the upper trough digs into the eastern
US. Medium range ensemble guidance and deterministic GFS and UKMET
are in good agreement with pushing the associated cold front quickly
across the region Thursday morning/Thursday afternoon. However, the
ECMWF continues to be 6-12 hours slower, and much wetter, with the
front. Forecast continues to track with the former solutions.
Moisture return will be limited, with only slight chance to chance
POPs generally over the northeast half of the forecast area
Thursday. Highs Thursday in the low 50`s north to mid/upper 50`s
south. As impressive dynamics/height falls and a strong surge of
cold, arctic air reaches the local area Thursday night, cannot rule
out light snow/flurries for the Maryland Eastern Shore. Lows drop
into the upper teens to low 20`s inland to upper 20`s near the
coast. Cool, breezy, and dry Friday as the latest GEFS indicates
850mb temperatures around -10 to -12C (-2 standard deviations).
Highs are expected to warm only into the upper 30`s to low 40`s. Add
in a breezy northwest wind and wind chills may only warm into the
mid 30`s. Dewpoints in the upper single digits to teens will allow
temperatures to drop into the 20`s (teens possible inland if trends
continue) Friday night under a clear sky. 850Mb temperatures progged
to moderate slightly Saturday (-6 to -8C) as cold high pressure
centers over the region. Less mixing will result in another cool
day, with highs back around 40 under a mostly sunny sky. High
pressure forecast to slide offshore Saturday night as the next storm
system approaches from the west.


VFR conditions at all area terminals this morning, with VFR
conditions to prevail through much of the upcoming period. High
pressure slides out of the Ohio Valley and directly over the Mid
Atlantic Region tonight into Mon. VFR conditions persist today as
low pressure over the Gulf Coast slowly lifts northeast through
Sunday night. Light rain currently over the Western Carolinas will
spread east across SW VA/Central NC through midday today, pushing
toward area terminals by sunset this evening. Ceilings will remain
AOA 12kft through this period, before lowering as pcpn arrives
through the night Sunday evening. MVFR ceilings expected, with
brief LCL IFR possible at RIC after Midnight Sunday night and
towards Monday morning at SBY, PHF, ORF, and ECG.

Outlook: Rain (briefly) moves out early Monday, with VFR conditions
returning. High clouds once again thicken and lower through the
aftn on Mon ahead of next system. Steady rain to overspread the
area from sw-ne late in the evening and overnight as shortwave
energy streams into the area via the upper ridge which is also
flattening overnight. High confidence of MVFR to IFR cigs/vis
(and maybe even LIFR conditions) during this period. Rain
continues through the day on Tuesday before tapering off Tue Night.
widespread mvfr/IFR returns Tue night, with conditions recovering
to VFR behind the system on Wed.


Latest surface analysis centers high pressure just west of the
waters this morning. The result is a diminishing north to northwest
wind to around 10-15 knots. Waves 1-3 feet and seas 2-4 feet. High
pressure settles over the waters today with flow veering from the
northeast to south to southeast late today into this evening. Speeds
generally at or below 10 knots. Waves and seas subside to 1-2 feet.
High pressure slides offshore tonight as low pressure develops along
the Southeast coast. Low pressure then lifts off the Mid-Atlantic
coast Monday as high pressure builds in from the northwest. Flow
becomes northwest Monday afternoon, increasing to 10-15 knots (up to
20 knots southern coastal waters). Winds then become onshore Monday
night and Tuesday as high pressure centers over the Northeast and
another area of low pressure lifts along the Southeast coast. SCA
conditions are possible Tuesday afternoon as the gradient
strengthens and speeds increase to 15 to 20 knots. Seas build to 4-5
feet late Tuesday with waves in the lower Bay building to 2-4 feet.
SCA conditions possible into Tuesday night as low pressure lifts
just offshore of the Mid-Atlantic coast. Flow becomes west-northwest
10-20 knots late Tuesday night, with seas still 4-6 feet. Sub-SCA
conditions all waters Wednesday with a northwest wind 10-15 knots. A
strong cold front Thursday will usher in the coldest and driest air
mass of the season Thursday night through Friday night. Strong SCA
(minimal Gale) conditions are possible.




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