Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 250146 AAA

Area Forecast Discussion...UPDATED
National Weather Service Baltimore MD/Washington DC
946 PM EDT Sat Mar 24 2018

Low pressure will pass by well to the south tonight and high
pressure will build overhead Sunday through Tuesday. High
pressure will move offshore Wednesday and a cold front will pass
through late next week.


Low pressure will pass by to the south tonight as high pressure
over Canada builds south into our area. The track of the low
will be far enough south to keep dry conditions for the vast
majority of the area this evening, and although a period of
light snow remains possible across southern portions of
Highland, Augusta and Nelson Counties, evening radar trends and
latest short term model guidance indicates that the chances are
lowering and the accumulating snow will remain south of these
counties, and no impact is expected.

Ahead of the building high pressure, a pressure surge/low level
cold front will cross from north to south into the region
overnight and into early Sunday morning at the same time as a
robust upper vort moves southward across PA/NJ. This may touch
off some light snow showers or flurries overnight and into
Sunday, mainly from DC north/east. No accumulation/impact is


High pressure will continue to build south into our area Sunday.
The upper-level low over upstate New York will move off the New
England coast, but shortwave energy from the upper-level low
will drop south through eastern Maryland. A couple snow or rain
showers cannot be ruled out, especially near the Bay but again
the airmass is very dry so any precipitation will be light and
no snow accumulation is expected with surface temperatures well
above freezing.

High pressure will continue to build overhead Sunday night
through Monday night, bringing dry and chilly conditions for
this time of year.

The high will begin to shift toward the east coast Tuesday and a
return flow will develop. More chilly conditions are expected
for this time of year. The return flow will allow for warm and
moist air to overrun the surface colder air in place resulting
more clouds. There may be just enough lift for some light
precipitation, mainly across the Allegheny and Potomac Highlands
where overrunning will be a bit deeper farther away from the
high. Should precipitation move in early enough Tuesday, a light
wintry mix is possible across these areas. Confidence remains
very low at this time.


Upper level pattern over the western Atlantic features a
meandering cutoff 500hPa low spinning well east of the Mid-
Atlantic coast early Wed with a short wave upper level ridge
extending from the northeast Gulf of Mexico into New England.
The blocky upper level pattern over the central Atlantic will
prevent much movement with the 500 hPa cutoff low. Meanwhile the
upper level low over SW U.S. on Wed will eventually move east
across the southern state...but is not expected to phase with a
northern upper low that sweeps across the northern fringe of the
U.S. late in the week.

From mid-week until Friday expect temperatures to moderate
relative to the below normal readings experienced since mid-
March. A warm front will try to move north on Wednesday but will
struggle to do so as high pressure still extends along the m
Mid-Atlantic. A slow- moving cold front will approach the region
on Thursday and will continue a chance of precipitation. Timing
of the cold front looks to be slower than GFS/GEFS
suggests...and like a slower timing for late Thur night into the
day on Fri. The front will move off the coast by Fri evening
allowing for weak high pressure to build into the region on Sat.
Also, there is quite a spread in temperatures Wed- Fri ahead of
the next cold front. The 12Z GFS/MOS was much warmer than all
earlier 00Z guidance, and prefer the 00Z/EC-MOS guidance temps
that are cooler.


VFR conditions are expected through Tuesday night. A pressure
surge/cold front will cause north to northeast winds to gust
around 15 to 20 knots late tonight through midday Sunday. A few
flurries are possible with this feature tonight and again with
another upper-level disturbance Sunday. However, most places
will end up dry and no accumulation is expected.

High pressure will build overhead Sunday night through Monday
night before shifting toward the east coast Tuesday and Tuesday

The remnants of high pressure Wednesday will be along the
eastern seaboard...and a warm front will be in the could see some MVFR to locally IFR CIGS in any
precip associated with this front. Once the warm front lifts
north...probably sometime on Wed...then conditions should be
mainly VFR with scattered MVFR CIGS in precip. A cold front will
slowly cross the area late-Thu and early Fri with brief
MVFR/IFR cigs in precip.


Weak high pressure will remain overhead through this evening. A
pressure surge/cold front will pass through the waters late
tonight into Sunday. A Small Craft Advisory is in effect for the
waters during this time. High pressure will continue to build
toward the area Sunday night through Monday night before
shifting toward the coast Tuesday. A Small Craft Advisory may be
needed for middle portions of the Maryland Chesapeake Bay
Monday. The gradient should be light enough for winds to remain
below SCA criteria Monday night through Tuesday night.

Southerly flow once the warm front moves north on Wednesday will
be below SCA levels.


MARINE...Small Craft Advisory from 1 AM to 6 PM EDT Sunday for ANZ530-
     Small Craft Advisory from 6 AM Sunday to 6 AM EDT Monday for
     Small Craft Advisory from 1 AM Sunday to 6 AM EDT Monday for


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