Area Forecast Discussion
Issued by NWS Wakefield, VA

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FXUS61 KAKQ 201739
AFDAKQ

Area Forecast Discussion
National Weather Service Wakefield VA
1239 PM 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/...
Adjusted pops/temps to better reflect current conditions this
afternoon.

pvs dscn:
High res data indicating the band of mdt to lclly hvy rainfall
across the piedmont weakens as it quickly moves east across the
fa next svrl hrs with it pushing toward the coast after 18Z.
Only sct pcpn expected behind this initial band of rain. Thus,
minor changes made to crnt grids with the cat/likely pops next
few hrs ramping down west to east as the day wears on. QPF one
quarter to one half inch west of I95, a quarter inch or less
east of there. 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 /18Z FRIDAY THROUGH WEDNESDAY/...
Rain moving across the fa this afternoon ahead of an approaching
warm front. Initially, the pcpn is falling out of a fairly high
cloud deck (6-8K FT), but obs to the west showing IFR stratus
overspreading the western piedmont as the second wave of pcpn
tracks across the region. Thus. a TEMPO group was added over
the next 2-4 HRS given the changable conditions. Latest data
continues to show abundant low level moisture tonight along with
areas of fog/drizzle. This will likely result in widespread IFR
(with local LIFR) conditions from this evening right on though
abt 15Z Sat. Expect a slow improvement toward the end of the
forecast period.

OUTLOOK...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/MPR
SHORT TERM...MAS/MPR
LONG TERM...SAM
AVIATION...MPR
MARINE...BMD


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