Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 230130
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
930 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/...
Cold front has pushed into North Carolina this evening. 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 in southwest Missouri.

The last of the rain is exiting southern Maryland. However,
there`s another batch in southwestern Virginia. This should
slide along the southern portion of the CWA during the middle of
the night, with drier air winning the battle farther north.
After this rain exits, there could be another break late tonight
into early Sunday morning.

Lower clouds have been clearing out of northern portions of the
area, although the lower dew points are lagging in PA. With the
thin clouds and rain-saturated conditions, there could be a
little fog before drier air advects in (already seeing some
reductions in visibility at MRB and OKV). Lows tonight will be
in the 40s for most locations.

During the day Sunday, it now appears that drier Canadian air
will press southward far enough to dry us out. The northern half
of the area may even see filtered sun through cirrus for the
first half of the day, with cloudier conditions south. The
overrunning rain due to the proximity of the frontal zone will
persist across the far south (central VA and southern MD),
but it should be light in nature as the best deep moisture will
be suppressed in southern VA. Highs will be coolest in the
south in the mid 50s, but perhaps poking into the 60s in the
north.

&&

.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 revisited 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 /01Z SUNDAY THROUGH THURSDAY/...
Lower clouds have scoured out at most locations, but linger in
scattered fashion, so there is some concern with them filling in
as briefly happened at DCA. There is also concern for fog
developing, especially MRB, before drier air can work in.
Rainfall has moved out for the night (and most of Sunday for
that matter) except at CHO, where interludes of light rain will
continue. Cig forecast most uncertain for CHO, as low level
moisture will linger just to the south. 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. Added the middle Potomac portion through tonight,
although latest obs suggest the area may be stabilizing. SCA
likely to continue Monday and Tuesday as the low moves northeast
up the Atlantic Coast. While rain will move through at times,
amd 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. Given trends this
evening, have issued a Coastal Flood Advisory for St. Marys
County, although it will be a threshold event.

Coastal flood 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...Coastal Flood Advisory until 2 AM EDT Sunday for MDZ017.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 6 AM EDT Sunday for ANZ536-539-542.
     Small Craft Advisory until 6 PM EDT Sunday for ANZ531-540.
     Small Craft Advisory until 6 AM EDT Monday for ANZ532>534-537-
     541-543.

&&

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



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