Area Forecast Discussion
Issued by NWS Wakefield, VA

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FXUS61 KAKQ 200841
AFDAKQ

Area Forecast Discussion
National Weather Service Wakefield VA
341 AM EST Fri Jan 20 2017

.SYNOPSIS...
High pressure pushes offshore today as low pressure tracks
across the Midwest and into the Great Lakes region. The
associated warm front lifts north into the area through tonight.
A complex area of low pressure will affect the region early
next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Latest sfc analysis shows 1017 mb high pressure centered over
the Delmarva with a warm front stretched across the SE states.
Aloft, a mid-level ridge axis is positioned along the eastern
seaboard. The sfc high and upper ridge will push offshore today
as the warm front associated with sfc low pressure over the
Midwest approaches the Mid Atlc. Resulting overrunning pcpn
will overspread the fa from west to east through the day. PoPs
remain categorical for the Piedmont and northern half of the
area, and 50-70% elsewhere. Best chance of rain along I95 will
be midday, then early-mid aftn near the coast. QPF one quarter
inch or less. Highs in the low/mid 50s most areas; upr 50s to
near 60 NE NC.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/...
Any steady/lingering rain exits off the coast by late this
aftn/early eveng. Otw, tsctns continue to show plenty of low
level moisture across the fa tonight. Given a nearly saturated
airmass and the warm front in the vicinity, maintained patchy
fog/drizzle in the forecast. Lows 40 to 45.

Saturday starts out with fog/drizzle then remains cloudy.
Moisture from an approaching southern stream system progged a
bit slower to move north so have kept PoPs no higher than 30-40%
far southern areas, with silent PoPs near and NE of RIC. Rather
mild despite the cloud coverage. Highs 55-60 near the water,
60-65 west of the bay.

Models begin to diverge with the approaching system from the south
Saturday night and especially Sunday. Initial low tracks NE along
the spine of mts while secondary low pressure develops on an
advancing frontal boundary from the south. Model differences
lead to a low confidence temp forecast but high confidence PoP
forecast. Yes it will rain, but uncertainties continue regarding
whether pcpn will be entirely stratiform or if some convection
can develop. Parameters are favorable for thunderstorms however,
at least over southern areas, so maintained the chance of
thunder in the forecast for Sunday. Also kept moderate pcpn
rates in the grids, with locally heavy downpours possible as
mentioned in the HWO. Highs mid-upr 50s north to mid 60s south,
but temps could easily end up higher or lower, especially over
southern areas.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Upper level energy currently over the Gulf of Alaska is forecast to
lift into the Mid-Atlantic region Sunday night. There are still some
spatial and timing differences in handling of the associated surface
low and frontal features in the 19/12Z guidance, but confidence is
high that widespread precipitation continues Sunday night. POPs have
been raised to categorical as upper level forcing and moisture are
plentiful. The surface low is progged to lift along the Mid-Atlantic
coast Monday as the upper low remains over the region. Best moisture
flux and theta-e advection progged to be offshore, but have included
a slight chance mention of thunder across the southeast local area
Monday. Have trimmed daytime highs back a few degrees into the mid
to upper 50`s. Upper/surface low pressure lifts northeastward away
from the region Monday night and Tuesday, with precipitation chances
winding down Tuesday afternoon. Upper/surface low pressure builds
into the region Tuesday, sliding offshore Tuesday night as the next
storm system approaches the region. Highs Tuesday generally in the
mid 50`s  under a partly cloudy to mostly cloudy sky. A cold front
associated with an upper low lifting over the Great Lakes region
progged to push across the region Wednesday into Wednesday evening.
Moisture and forcing look rather meager at this point, so have kept
silent POPs. Warmer Wednesday, with highs in the upper 50`s north to
low 60`s south. Shortwave energy progged to push across the region
Thursday, but a lack of moisture and westerly flow will result in
ongoing silent POPs. Highs Thursday generally in the mid 50`s. Lows
during the period will generally be in the 40`s, with the next
chance for sub-freezing temperatures inland Thursday night.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
As of 06z...High pressure over coastal portions of the Mid
Atlantic States will move off the coast early this morning. Low
pressure will over the Mid Mississippi Valley will move
northeast into Ohio. An upper level shortwave lifts northeast
through the Mid Atlantic States today. Included some low vsbys
that could last through mid morning for KECG where some fog has
already developed in the vicinity.

A broken layer of cirrus clouds over the area will increase
with lower clouds moving in later this morning. Precipitation
develops from the southwest this morning and spreads to the
coast in the afternoon. MVFR conditions are expected with the
precipitation. IFR ceilings are possible at RIC and SBY late in
the day. Winds will be light through the period.

OUTLOOK...IFR conditions are indicated for most of the area
tonight into Saturday morning with fog and drizzle possible.
Abundant low level moisture and weak surface flow will promote
reduced aviation conditions through much of the day Saturday.
Ceilings and visbilities will deteriorate again Saturday night
and Sunday morning with IFR possible at each of the TAF sites.
Periods of widespread rain are expected Sunday through Monday as
a strong low pressure system moves from the southern Great
Plains and across Virginia Monday to off the New jersey coast
Tuesday. This will result in unfavorable conditions for
aviators. The weather improves by Tuesday.

&&

.MARINE...
Winds generally se aob 10kt today as high pressure moves offshore
this morning and a warm front lifts nwd through the region. Long
period swell will allow 3-4ft seas to persist through today. Winds
become more n-ne tonight as a weak coastal trough develops just
off the Mid Atlantic coast...becoming more se Sat aftn into Sat
night with speeds remaining around 10kt or less. Seas subside to
2-3ft tonight through Sat night. Waves 1-2ft.

Onshore winds ahead of a strong area of low pressure Sun will
increase to 15-25kt late Sun aftn/early evening through Monday.
A period of low end gales is possible...especially across the nrn
coastal waters during this time. The combination of onshore winds
and a very tight pressure gradient due to the low rapidly
intensifying (causing potential pressure falls of 4-8mb) will push
seas to 5-6ft south/7-10ft north late Sun and upwards of 6-8ft
south/8-12ft north on Mon. Waves generally 3-4ft (5ft mouth of Ches
Bay). The sfc low tracks just ne of the Delmarva Peninsula by Tue
morning. Although the airmass being pulled into the region on the
back side of the low is not significantly cooler Tue than the
previous conditions Mon night, the sfc pressure gradient will
remain very tight with nw flow aloft, a shortwave passing overhead,
and a decent 80-90kt jet nosing over the waters. In addition,
pressure rises of 4-6mb will lend some credence to the overall
instability and result in nw winds continuing around 15-25kt (gusts
up to 30kt over the coastal waters) through Tue. Seas subside very
slowly to an average of 4-7ft by late Tue aftn (possibly still 8ft
near 20nm far nrn coastal waters) in the offshore/nw winds. Waves
3-4ft. High pressure and a warmer airmass advecting over the waters
from the sw Tue night will act to stabilize conditions and allow
winds to slowly subside overnight. Seas average 3-5ft/waves 1-2ft
late Tue night.

&&

.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...None.
NC...None.
VA...None.
MARINE...None.

&&

$$
SYNOPSIS...MAS
NEAR TERM...MAS
SHORT TERM...MAS/MPR
LONG TERM...SAM
AVIATION...MAS/LSA
MARINE...BMD


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