Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 221908
AFDLWX

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

.SYNOPSIS...
A cold front will remain stalled to the south through Sunday.
Low pressure will develop along the boundary...impacting our
area through early next week. Low pressure will move out to sea
Wednesday. A cold front may impact the area late in the week.

&&

.NEAR TERM /THROUGH SUNDAY/...
Latest surface analysis depicts a cold front continuing to slide
southward across southern Virginia, accompanied by a weak wave
of low pressure. High pressure is centered over the Great Lakes
and pushing east. Another low pressure is located to the south
in Mississippi. Aloft, a trough of low pressure extends from
Quebec southwestward to a closing-off low near St. Louis.

Tonight, the front and weak low pressure wave will continue
sliding southeastward away from our region, allowing cooler
Canadian air associated with the high pressure to continue
sliding southward into our region. Some instability aloft could
bring a rumble of thunder to central Virginia and far southern
Maryland over the next few hours, but otherwise it should be
just some rain. As the shortwave aloft separates from the low
closing off to the west and shifts east, precipitation should
gradually wind down this evening from northwest to southeast,
though with the front stalling in North Carolina and the closed
low to the west starting to approach, rain may not completely
end in far southern parts of the CWA. Temperatures will fall
into the 40s.

During the day Sunday, it now appears that drier Canadian air
will press southward far enough to dry us out, though there may
still not be much sun. The exception again will be the far
south, central VA and southern MD, where some rain may linger
through the day due to the proximity of the front and
approaching closed low. Further north, there may be some breaks
of sun, but otherwise it should be fairly cloudy and cool, with
highs in the 50s to near 60.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
Closed low aloft and associated surface system will continue
sliding east across the southern US Sunday night, then turn
northeast up the Atlantic Coast by Monday night. This will cause
rain to overspread the region again, with temperatures remaining
cool. An increasing northeast wind as the surface low
strengthens will add to the rather uncomfortable weather,
especially compared to recent warmth. Significant rain is
possible, perhaps 1 to 3 inches. If heavy rainfall becomes
concentrated, it is possible some flooding could occur, but
right now, given it has generally been dry and there remains
great model inconsistency about where any heavy rain may
ultimately fall, do not have any plans for flood watches yet.
This will no doubt be revisted by future shifts.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Coastal low pressure will track north along the Carolina
coastline Tuesday. Forecast guidance depicts a broad area of
precipitation with this system as the upper level low is nearly
stacked on the coastal low. Rain is expected across the region
Tuesday into Tuesday night. Bands of heavier rain are possible
during this time as easterly LLJ pumps moisture into the Mid-
Atlantic. Stable conditions expected with temperatures in the
50s/60s.

The coastal low will be off the Delmarva coastline Wednesday
and rain will come to an end across the Mid-Atlantic region.
Sunshine will help temperatures get closer to 70 on Wednesday.
Winds become southerly Wed night ahead of the next cold front. A
cold front will pass the region Thu-Fri and showers and
thunderstorms are possible. Temperatures will become above
normal Thu-Fri.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
MVFR/IFR cigs and vis with rain across the region will slowly
improve as drier Canadian air slides into the region this
evening. Expect VFR by later tonight except CHO, where low
clouds and rain may linger through Sunday. Winds will be
northerly but generally less than 15 knots. Conditions likely to
return to IFR all terminals Sunday night and linger at MVFR/IFR
levels through Monday night with increasing northeast winds as a
coastal low makes its way northeast up the Atlantic Coast.

Low ceilings and vsbys possible Tuesday-Tuesday night as rain
continues.

&&

.MARINE...
Generally marginal SCA conditions across the bay and some
adjacent waters through Sunday night as high pressure nudges in
from the northwest while low pressure approaches from the
southwest. SCA likely to continue Monday and Tuesday as the low
moves northeast up the Atlantic Coast. An isolated thunderstorm
may reach the central Chesapeake Bay and lower tidal Potomac
over the next few hours, but otherwise not expecting thunder
through Tuesday. Condtions may start to improve Wednesday.

&&

.TIDES/COASTAL FLOODING...
A persistent onshore flow has already significantly elevated
water levels in parts of the bay, with minor flooding having
occurred at Straits Point this morning. This potential will
continue through the next several days, with the greatest risk
of minor flooding occurring later Sunday through Tuesday as a
coastal low pressure moves northward into the region.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 6 PM this evening to 6 AM EDT Sunday
     for ANZ539.
     Small Craft Advisory from 6 PM this evening to 6 PM EDT Sunday
     for ANZ531-540.
     Small Craft Advisory until 6 AM EDT Sunday for ANZ542.
     Small Craft Advisory from 6 PM this evening to 6 AM EDT Monday
     for ANZ543.
     Small Craft Advisory until 6 AM EDT Monday for ANZ532>534-537-
     541.

&&

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



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