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fxus61 kakq 271331 
afdakq

Area forecast discussion
National Weather Service Wakefield Virginia
931 am EDT Thu Apr 27 2017

Synopsis...
a cold front approaches the mid Atlantic region today, stalling
near the mountains tonight. High pressure prevails off the
southeast coast the rest of Friday through the weekend. The next
cold front pushes across the region early next week.

&&

Near term /until 6 PM this evening/...
update...based on webcams and observation trends, any fog on the
Maryland lower Eastern Shore has lifted into low stratus and will
continue to lift and scour out over the next hour or so as
south winds increase. Meanwhile, stratocumulus is moving
offshore as of 900 am with high cirrus pushing in from the west.
Additional mid to high level clouds expected to push into the
eastern Piedmont this afternoon as a cold front approaches the
Ohio Valley. This may hamper full warming potential in these
areas and adjusted high temps down a degree or two as a result.
Also adjusted Atlantic beaches down 5-10 degrees for highs with
temps starting out in the upper 50s this morning and an onshore
wind component over colder waters. Otherwise, today will be warm
with fair weather cumulus development by this afternoon.

Previous discussion...
latest GOES water vapor imagery depicts a broad/anomalous upper
trough encompassing much of the western/central conus, with an
upper level ridge over the east. At the surface, weak area of
low pressure is located offshore the northeast coast with high
pressure well offshore extending westward over the southeast. A
cold front associated with the upper trough is located along the
Mississippi River valley. A dense fog advisory remains in
effect for the lower Maryland Eastern Shore, with an area of
dense fog visible in the obs and on satellite. Otherwise, only
some patchy fog inland as light southerly flow and relatively
dry low levels have kept widespread fog at Bay.

Fog expected to erode/lift shortly after daybreak in response to
quickly warming temperatures. The upper level ridge axis slides
offshore late morning as the central US trough de-amplifies and
lifts over the Ohio Valley and into the Great Lakes region. An
associated cold front will reach the central Appalachians late
today. Increasing return flow ahead of the front (southwest
gusts of 20-25 mph) and 850mb temperatures around +14 to +16c
(+1 Standard deviation) results in a warm day, with temperatures
generally 10+ degrees warmer than yesterday. Highs generally in
the mid 80's. Cooler along the coast. Increasing mid to upper
level clouds late today may keep some of the far western
Piedmont in the low to mid 80's. Otherwise, outside of some high
clouds spreading over the region today from a decaying line of
showers, a mostly sunny sky is expected.

&&

Short term /6 PM this evening through Saturday/...
showers and thunderstorms progged to develop along the cold
front this afternoon from the Ohio Valley to the southeast. Hi-
res guidance pushes a weakened version of the convective line
into the Piedmont early this evening as the upper level forcing
becomes displaced from the deepest Gulf moisture. Short term
guidance indicating better moisture return compared to 24 hours
ago thanks to a developing 30-40 kt low level jet. Good moisture
flux advects anomalous precipitable water values into the
region ahead of the line/pre-frontal surface trough. Thermal
soundings indicate elevated instability as height falls and cold
air advection aloft steepen mid level lapse rates. Showalters
range from -1 to -2. Deep layer shear progged around 30-40 knots
due to increasing winds aloft. However, given the lack of
overall forcing and the convective line outracing the front,
have kept pops in the chance category tonight. Main threat from
thunderstorms will be locally heavy rainfall. Mild tonight, with
lows generally in the mid to upper 60's.

Weak surface trough/convergence boundary stalls near the coast
Friday morning as the deepest moisture pushes offshore. Even
though the best moisture pushes offshore, enough moisture and
instability near the coast will keep mention of isolated to
scattered showers and thunderstorms in the forecast through
early-mid afternoon. Meanwhile, the subtropical ridge amplifies
off the southeast coast Friday. Early morning clouds and
convection will temper temperatures from reaching their full
potential Friday afternoon. Highs similar to today, generally in
the mid (possibly upper) 80's. Cooler near the coast.

Heights continue to build into Sunday as 850mb temps warm to +16
to +18c (+2 Standard deviations). The result will be the warmest
day of the season with widespread readings in the low 90's.
Dewpoints in the 60's will push heat index values into the mid
90's inland. A backdoor front progged to drop into the northern
mid-Atlantic region late Saturday, but models indicate large
spatial and timing differences. While the models indicate a
great deal of instability, soundings indicate a cap just above
850mb. Moisture is also limited with precipitable water values
at or below 1.25 inches. Will maintain slight chance pops across
the north near the dropping front, but believe sea-breeze
boundaries will struggle to overcome the lack of moisture and
warm temperatures aloft.

&&

Long term /Saturday night through Wednesday/...
temperatures are expected to remain well above normal through
sun as an upper level ridge remains anchored just off the East
Coast. A backdoor cold front could affect nrn portions of the
area Sat night thru Sun morning with a slgt chc of showers, then
a slowly approaching cold front from the west could produce
isolated or widely sctd showers or tstms sun aftn into sun
evening, especially wrn half of the region. Lows Sat night in
the mid 60s to near 70. Highs on sun in the upper 70s to mid
80s.

That cold front will push thru the mts by late Mon, then cross
the area and move off the coast Mon night into Tue morning. Have
high chc to likely pops for showers/tstms during this period.
Highs on Mon in the upper 70s to mid 80s. Lows Mon night mainly
in the upper 50s to mid 60s. Weak high pressure will provide dry
wx for later Tue morning thru at least most of Wed, as it
slides from the Gulf Coast states to off the southeast coast. Highs on
Tue in the 70s, and mainly in the mid to upper 70s on Wed.

&&

Aviation /13z Thursday through Monday/...
outside of IFR conditions due to fog across the Maryland lower
Eastern Shore, widespread VFR conditions observed early this
morning. Light southerly winds and relatively dry low levels
indicated in soundings will limit overall fog development but
some early morning patchy fog possible north and east of kric.
IFR conditions prevail thru early morning for ksby, otherwise
sky clear.

Cold front approaches from the west today with increasing
southwest flow late morning through the afternoon. Expect gusts
of 20-25 knots. Scattered afternoon cumulus expected inland around
4-6kft above ground level. Weakening line of convection expected to push across
the region this evening through late tonight. Lower
ceilings/visibilities will be tied to convection.

Outlook...next frontal boundary will provide a focus for more
shower/tstm development late Sat. Cigs/vsbys lower in any
convective activity.

&&

Marine...
a cold front approaches the waters today resulting in an
increase of south and southwest winds through tonight. Deep low
pressure over the upper Great Lakes will move north into Canada
which will relax the pressure gradient by Friday.

Southeast to south winds were generally 10 knots or less early
this morning. Seas subsided overnight but remain 4 to 5 ft north
of Parramore Island. While there may be lull in 5 foot seas late
this morning...they are expected to build once again late today
and into tonight as winds increase.

Replaced Small Craft Advisory for hazardous seas with a Small Craft Advisory. This is to avoid
confusion with winds increasing today. The Small Craft Advisory was also expanded
to anz654 (parramore island to cape charles) where Small Craft Advisory
conditions are expected to develop by this afternoon. There is
indication the Small Craft Advisory may be needed for the rest of the coastal
zones for a short period this evening but will let the day shift
assess the need. Elsewhere conditions are expected to stay below
Small Craft Advisory. Although winds over land are expected to gust over 20 knots
today...the cool water will inhibit mixing over the marine area.

The cold front that approaches the waters today will dissipate
over the area Friday morning. A disorganized pressure pattern
will produce light winds over the waters Friday. Seas are
forecast to subside to below 5 feet by midday Friday. Benign
conditions are indicated for the marine area through the
weekend. Another deep low pressure system will move through the
upper Midwest early next week. This along with an approaching
cold front will increase the pressure gradient locally and
another Small Craft Advisory may be needed starting Monday.

&&

Tides/coastal flooding...
there is gradual improvement in water levels that have been
elevated by a new moon and long period swells. Some locations
will continue to have high tides get within a few tenths of a
foot of minor flood. At this time...the high tide cycle early
Friday morning at Bishops Head Maryland touches minor flood.

&&

Climate...
it appears likely that Richmond and Norfolk will end the month
with the warmest April on record. Warm temperatures during most
of the month combined with an unseasonably warm period to end
April are expected to push the average temperature above that
which occurred in 1994. At Richmond, the previous record was
63.2 and at Norfolk it was 64.7. Both were set in 1994. This
month's temperatures could be around a degree above those
values.

&&

Akq watches/warnings/advisories...
Maryland...none.
NC...none.
Virginia...none.
Marine...Small Craft Advisory until 1 PM EDT Friday for anz650-652-654.

&&

$$
Synopsis...alb/bmd
near term...bmd/Sam
short term...Sam

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