Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 240934

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
534 AM EDT Fri Mar 24 2017

A warm front will cross the region today. A low pressure system
will then approach the region on Sunday, and cross the area
Sunday night into Monday. Another system will cross the region


Latest surface analysis shows high pressure sliding east off the
Atlantic coast and a warm front approaching from the west.
Aloft, a vort lobe is rotating eastward ahead of the warm front,
which when combined with warm advection, is supporting a band of
light rain which is moving into the region. The forecast for the
region remains tricky as temperatures in many spots are either
side of freezing. Southeast winds have helped some areas stay
above, while other spots which have gone calm have dropped
below. With rain now almost on our doorstep and temperatures
still below freezing in some areas, have issued freezing rain
advisory for northwestern parts of the CWA (W MD, E WV, N VA)
through 9 AM. May have to extend or expand based radar and temp
trends. Will continue to follow closely.

Otherwise, the band of rain should fall apart as it approaches
the I-95 corridor this morning, and afterwards, southerly winds
should start flooding the region with much milder air. While
clouds should remain common today, the gusty south wind should
elevate most places into the 50s, with most of Virginia and West
Virginia likely to hit 60. Some warm interior valleys of
eastern West Virginia may crack 70.


Southerly winds and milder air flooding the area will be the
main theme tonight through Saturday evening. While a ridge will
be in place aloft and high pressure will not be far off the East
Coast at the surface, it will be rather dirty, with plenty of
high and mid clouds. However, with very warm air surging north
and some breaks of sun expected, we still expect Saturday to be
the first day with widespread 70+ temps since March 9th. IAD`s
record is only 76, but DCA and BWI, who`s records include the
old downtown offices, have records into the mid 80s.

Saturday night into Sunday morning we will continue to watch
the potential for a back door cold front to slip back south
across the region, particularly Maryland. Uncertainty remains,
as guidance has continued to flip back and forth on this
somewhat, but right now it looks like most of our forecast
region will stay in the warm sector. However, with the next
system moving in later Sunday and Sunday night, clouds and
showers will keep temperatures down on Sunday. So, Saturday is
definitely the better day this weekend. With limited if any
instability, we don`t expect much if any thunder through
Sunday night, so have kept it out of the forecast for now.


Low pressure currently over CO/NM will continue to drift east
to the Midwest through Saturday night before dissipating near
the Great Lakes under a northern stream ridge Sunday. A second
low currently off California will trail the first low, reaching
the Midwest Monday night before reaching the eastern Great Lakes
Tuesday (and also dissipating) per 00Z ECMWF/GFS. Continued
moist southwesterly flow warrants high chance PoPs for the LWX
CWA Monday through Tuesday. Possibly a break in action, so
Monday night was kept low at this time and Tuesday was raised to
likely PoPs across the CWA.

Instability possible Tuesday ahead of the cold front, so slight
chance thunderstorms were maintained. Continued SWly flow
brings max temps well into the 70s Monday/Tuesday assuming no
widespread rain.

High pressure to the south starting Wednesday maintains above
normal temperatures through the rest of the work week.


Generally VFR through the TAF period and beyond into Saturday
night. Main concern is whether temperatures will be low enough
to cause freezing rain as a band of precipitation associated
with the passing warm front moves through this morning. Most
terminals should warm enough to keep it plain rain, but there
remains the chance of some freezing rain at MRB where temps may
not have time to warm. Further southeast, rain may dissipate
before even reaching BWI/IAD/DCA, but if it does reach there,
temps should be warm enough for plain rain. Otherwise, gusty
southwest wind develops today with the warm front passing. This
evening, as low levels decouple, there could be some low level
wind shear as the wind a few thousand feet up will remain quite
strong even as surface winds become much lighter. Winds may be a
bit lighter on Saturday than today. Sub-VFR cigs and vis become
a concern Sunday and especially Sunday night as a low pressure
system moves in with some showers. Winds will be uncertain as a
back door front tries to drop south into the area, with the
greatest uncertainty around MTN/BWI.

Southwesterly flow from low pressure to the west/north Monday
and Tuesday brings rain showers to the DC metros Monday and
Tuesday with a low thunder threat Tuesday.


SCA over the bay this morning will spread to all waters this
afternoon as warm front crosses the waters. Winds will gradually
diminish tonight. With very warm air over the cool waters on
Saturday, right now it looks like winds will stay below SCA, but
will need to be watched. SCA again possible Sunday with more
southerly channelling as a storm system approaches from the

Generally sub-SCA SWly flow prevails Monday and Tuesday with
thunder chances Tuesday.


MD...Freezing Rain Advisory until 9 AM EDT this morning for MDZ003-
VA...Freezing Rain Advisory until 9 AM EDT this morning for VAZ028.
WV...Freezing Rain Advisory until 9 AM EDT this morning for
MARINE...Small Craft Advisory until midnight EDT tonight for ANZ531>533-
     Small Craft Advisory from noon today to midnight EDT tonight
     for ANZ535>537-542.
     Small Craft Advisory until 6 AM EDT Saturday for ANZ534-543.
     Small Craft Advisory from noon today to 6 PM EDT this evening
     for ANZ538.
     Small Craft Advisory until midnight EDT tonight for ANZ530.
     Small Craft Advisory until 6 AM EDT early this morning for


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