Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Wakefield Virginia
457 am EDT Sat Apr 19 2014

Synopsis...
low pressure will track from northern Florida east northeast off
the southeast coast today through Monday...as high pressure builds
from the northern Great Lakes eastward across New England and off
the coast. A cold front will cross the area Tuesday afternoon into
Tuesday night.

&&

Near term /until 6 PM this evening/...
will continue with a blend of the latest GFS/European model (ecmwf) for the current
forecast from today through Monday. Low pressure over northern Florida early this morng
will start to lift east-northeast during today. Meanwhile...hi pressure over the
northern Great Lakes will build ewrd into southeast Canada. Northern edge of the rain
shield associated with that low to the S...will affect mainly the
southern half of the region into this eveng...as hi pressure north of the area
will hinder precipitation moving any farther north than a lyh to ric to wal
line. So...have 80%/70% probability of precipitation over NE NC and extreme southern Virginia...with
probability of precipitation decreasing to chance or slight chance as you go nwrd. Maximum temperatures will
range from the middle 50s to the middle 60s.

&&

Short term /6 PM this evening through Monday/...
the rain shield will gradually sink south-southeast tonight through Sun night...as
the surface hi pressure builds across New England and just offshr. This will
result in the low pressure area and its moisture to push a little
farther away from the southeast and middle Atlantic csts. So...decreasing chances for
rain from northwest to southeast...with improving sky conditions. Upper ridge of hi
pressure then builds over the region during Monday...resulting in a prtly or
mostly sny sky. Low temperatures tonight ranging from the lower 40s to the lower
50s. Maximum temperatures on sun ranging from 55 to 60 at the CST...to the
middle to upper 60s inland/Piedmont. Min temperatures will range from the upper
30s to upper 40s Sun night...with highs on Monday ranging from the upper 50s
to lower 60s at the CST...to the middle 60s to near 70 inland.

&&

Long term /Monday night through Friday/...
near seasonable normal temperatures will highlight the extended period
forecast. A cold front will bring showers to the local area on
Tuesday.

Southern stream associated coastal low slowly lifts northeastward off the middle-
Atlantic coast Monday night-Tuesday morning as a northern stream shortwave
digs over the Great Lakes region into the Ohio Valley. Associated
cold front will push toward the local area as the parent low lifts
across New England. Medium range guidance is in good agreement
with pushing the front through the local area Tuesday afternoon and
off the coast Tuesday evening. While the best dynamics will be over
the Ohio Valley as the front crosses the local area...a weaker
leading shortwave will combine with increasing winds aloft for
ample forcing for ascent along the front. Precipitation waters will begin
to recover as low level 850 mb flow increases. The result will be
scattered afternoon showers. Theta-E advection and temperatures in the
middle-upper 70s will also produce a marginally unstable...so thunder
cannot be ruled out...especially across the south.
However...dewpoints in the low-middle 50s...little cape/lift in the
mixed phase layer and modest shear will limit overall coverage.
Have only mentioned a slight chance Tuesday afternoon for thunder.
Remnant middle level moisture in northwesterly flow will coincide with the
trough axis over the local area Tuesday night-Wednesday morning...as
additional energy dives down the backside of the upper trough.
This will likely result in some middle level clouds Wednesday some
sprinkles possible...especially over the northern local area and Eastern
Shore. High pressure builds into the region Wednesday night-thurs. A
warm front is forecast to lift over the middle-Atlantic region Thursday
night-Friday as a western Continental U.S. Trough amplifies an upper ridge over the
east. Forecast remains dry through the end of next week...with a
front possibly impacting the region next weekend.

Temperatures will warm into the middle-upper 70s (to near 80 inland) thanks
to southerly flow in advance of the approaching cold front. Cooler Wednesday-
Thursday behind the front (nw-west winds) with highs generally in the
upper 60s-low 70s. Return flow on the backside of high pressure
located just offshore will warm temperatures back into the middle-upper 70s
Friday. Overnight lows generally in the upper 40s-low 50s except
Thursday morning when lows will be in the middle-upper 40s.

&&

Aviation /09z Saturday through Wednesday/...
currently noting MVFR conditions across southeast coastal sites, with
some local IFR impacting ecg early Saturday morning.

Strengthening low pressure over the Gulf of Mexico/Florida Panhandle
this morning will continue to track east-northeast off the southeast coast
into the Atlantic trough Sunday. Upper level clouds will be
persist over the forecast area through Sat. Swath of rain associated with the
system is falling from a 6-8kft deck, so expect a brief
improvement in ceilings at phf/orf in -ra or sprinkles. Vcsh f0r a
few more hrs, with more widespread rain showers reaching taf sites after
08z Sat. Northern terminals look to be too far north to see any
precip, but did bring a brief period of rain showers to ric between
10-15z before drying out as high pressure builds in the the NW,
helping to dry out the airmass and eliminate any precipitation chances
this aftn/evening. However, expect MVFR conds to persist at
orf/ecg through this evening.

Outlook: NE flow continues Sat night though Monday as high pressure
north of the area moves east and wedges south into the mid-Atlantic.
A cold front will push across the region Tuesday/Tuesday night,
with VFR conds returning Wednesday as high pressure builds into the
region.

&&

Marine...
latest observation reflect light north-NE flow over the waters this morning. Weather
analysis features surface low pressure (at the surface and aloft) over the
Florida Panhandle. This feature will continue to slowly push east-NE
along the Georgia/SC coast today. The result will be continued NE-east flow
over the waters, which will slowly increase from north to south. Small Craft Advisory
mainly for seas remains in effect over the coastal waters through
Monday, and an Small Craft Advisory has been hoisted for today over the Currituck
Sound with this package. Flags for the Lower Bay and lower James
follow shortly thereafter this evening, as the surface low will slowly
builds east-NE through the weekend and early next week (as 1030+mb surface
high pressure remains north of the waters through early next week).
Flags will be needed for the remainder of the Bay and possibly the
York/Rappahannock by as early as late tonight/early Sunday.

Conditions will continue to deteriorate tonight and through Monday,
with NE-east flow to persist through early next week. Seas will likely
remain 4-6 feet Sunday, likely building to 6-9 feet (highest south) as
NE winds increase later sun and early Monday in response to
tightening gradient. Headlines have been extended through the fourth
period (sunday ngt) for all coastal waters.

Flow returns to the east-southeast Monday night as low exits and gradient
slackens. Winds veer S-SW by Tuesday in advance of a weak cool
front, which will cross the waters Tuesday afternoon-evening. Winds
will back to the northwest behind the front with low end Small Craft Advisory conditions
possible Tuesday night-Wednesday. High pressure returns through the end
of the week.

&&

Akq watches/warnings/advisories...
Maryland...none.
NC...none.
Virginia...none.
Marine...Small Craft Advisory from 6 PM this evening to 6 PM EDT Sunday
for anz632-634-638.
Small Craft Advisory until 6 PM EDT Sunday for anz633.
Small Craft Advisory until 7 am EDT Monday for anz650-652-654-
656-658.

&&

$$
Synopsis...tmg
near term...tmg
short term...tmg
long term...Sam
aviation...mam
marine...mam