Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 220741
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
341 AM EDT Sat Apr 22 2017

.SYNOPSIS...
A cold front will stall to the south today. Low pressure will
develop along the boundary...impacting our area through early
next week. Low pressure will move out to sea Tuesday night and
high pressure over the Atlantic will impact our weather for
Wednesday. A cold front may impact the area late next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
The frontal boundary that caused the showers/thunderstorms
yesterday has shifted south of the area this morning with
northerly flow in the low levels being observed across the
region. At the same time, moisture/energy is streaming east-
northeastward along the frontal zone out ahead of a closed low
pressure system in the central Plains.

Therefore a wet day is expected today, with the most widespread
rain coming in two concentrated batches. First, widespread
shower activity is currently spreading into the area from the
southwest, and this will affect the region through the morning
hours, generally pulling east by around noon. Following this,
there may be a brief break in the activity in the early to mid
afternoon hours, although scattered showers may still be around.
Second more widespread period of rain, located over the
Mississippi River Valley as of early this morning, will then
move into the Mid-Atlantic states later this afternoon and into
the evening.

Temperatures will follow a non-diurnal trend today with highs
being observed in the early morning hours (in the 60s as of
this writing), and then temperatures falling into the 50s during
the day.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH MONDAY NIGHT/...
Periods of wet weather will continue across the Mid-Atlantic
region into early next week. Some drier air is expected to
nudge southward into the region tonight and into Sunday, and
this will shift the focus for the rain southward across central
and southern Virginia, with lower rain chances elsewhere. For
some areas, especially DC north, later tonight and Sunday may
actually end up being mainly dry, although will keep rain
chances in the forecast as the northern extent of the gradient
is uncertain, and the ECMWF is on the north end of the guidance
envelope. Lows tonight in the 40s for most locations, with highs
in the 50s under clouds on Sunday.

More widespread rain will then push back northward for Sunday
night through Monday night as low pressure system hits the
east coast and slowly trudges northward. By Tuesday morning, the
surface low center is still only progged to be near the Outer
Banks of North Carolina. By 12z Tuesday, NAM/ECMWF/GFS suites
all in relatively good agreement of a widespread long-duration
rainfall ranging from about 0.5" north to possibly 2-3" south.

Temperatures will be cool and relatively stable from Sunday night
through Monday night with clouds and rain. Lows both nights in
the 40s/50s, and highs in the 50s.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
Low pressure along the North Carolina coast Tuesday will slowly
move out to sea Tuesday night. High pressure over New England
will continue to wedge into the Mid-Atlantic during this time.
Warm and moist air from the Atlantic Ocean will overrun cooler
air near the surface...resulting in plenty of clouds along with
rain Tuesday. Rain should dissipate in coverage as the low moves
away from the area Tuesday night. The best chance for a soaking
rain Tuesday into Tuesday evening will be across central and
eastern portions of the CWA.

The low will continue to move away from the area Wednesday and
drier air should work its way into the area...allowing for some
sunshine to return. A weakening cold front may impact the area
Thursday. Bermuda high may control the weather pattern toward
the end of next week with much warmer and more humid conditions.

&&

.AVIATION /07Z SATURDAY THROUGH WEDNESDAY/...
Low clouds and rain showers will affect the region through today
with MVFR developing across the region this morning and
persisting through the day. Some areas of IFR are possible this
morning, especially BWI/MTN.

As drier air tries to work into the area tonight and Sunday,
improvement to VFR is currently forecast for most sites, with
the exception of CHO where the highest chances for continued
widespread low ceilings and rain exist.

Additional low stratus and rain will then overspread the region
later Sunday and persist through at least Monday night, with
sub-VFR conditions expected.

Winds will be generally N-NE through the period.

A soaking rain is likely Tuesday with subVFR conditions. Rain
may taper off Tuesday night...but subVFR conditions will likely
continue into Wednesday. Cigs/vsbys should gradually improve
Wednesday as drier air works its way in behind departing low
pressure.

&&

.MARINE...
North/northeast winds will intensify this morning with marginal
SCA winds developing across the Chesapeake Bay and lower tidal
Potomac. Periods of rain may limit mixing potential, but low
level wind surge will likely be enough to reach 20 knots. Gusts
will continue tonight as cooler air temperatures move over the
warmer waters, leading to increased mixing.

Marginal SCA may be needed again Sunday, but confidence low at
this time. SCA will then likely be needed Sunday night through
Monday night as coastal low develops offshore and northeast
winds intensify.

Coastal low pressure will impact the waters Tuesday before
slowly moving out to sea Tuesday night into Wednesday. A Small
Craft Advisory will likely be needed for portions of the waters
Tuesday through Tuesday night.

Weak high pressure will build over the waters later Wednesday
and a weakening cold front may impact the waters Thursday.

&&

.TIDES/COASTAL FLOODING...
A persistent onshore flow will develop behind a cold front
through early next week. Elevated water levels are expected
during this time...and minor flooding cannot be ruled out near
times of high tide...especially Sunday into Tuesday.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 7 AM this morning to 6 AM EDT Sunday
     for ANZ530>533-538>541.
     Small Craft Advisory from 11 AM this morning to 6 AM EDT
     Sunday for ANZ534-537-542-543.

&&

$$
SYNOPSIS...BJL
NEAR TERM...MM
SHORT TERM...MM
LONG TERM...BJL/MM
AVIATION...BJL/MM
MARINE...BJL/MM
TIDES/COASTAL FLOODING...BJL



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