Area Forecast Discussion
Issued by NWS Sterling, VA
FXUS61 KLWX 250802
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
402 AM EDT Sat Mar 25 2017
High pressure over the western Atlantic will be in control
today. A back door cold front will drop southwestward into the
area later tonight and Sunday. The front will lift back to the
north on Monday. Another cold front will drop back south across
the region later Tuesday or Tuesday night. The front will
stall to the south of our area through the rest of the week.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
As of 3am, an approximate 1032mb surface high pressure is
centered near Bermuda, 1006mb low pressure is centered over
eastern Oklahoma, and 1034mb surface high pressure is centered
over northern Ontario. The Canadian high pressure will shift
southeast to New England through tonight. This will cause a
backdoor cold front to cross the northern half of the CWA with
the Bermuda high causing southerly flow south of the cold front.
Today, very warm with temperatures 10 to 15 degrees above
normal. Most uncertain area for MaxT today is the northern tier
of counties where the southern section of an anafrontal zone
will persist. Thicker clouds and chances for rain may keep
temperatures in the mid 60s. Mid to upper 70s prevail south of
.SHORT TERM /6 PM THIS EVENING THROUGH MONDAY NIGHT/...
Confidence in a backdoor front and subsequent onshore flow/cold
air damming has increased, so temperatures were lowered below
guidance consensus particularly around Baltimore where low 50s
are currently expected. Also, patchy drizzle was added to the
Sunday forecast generally Blue Ridge and east. A sharp gradient
between warm southerly flow and cool easterly flow is expected
over southern portions of the CWA. Subsequent shifts will need
to focus on this for the MaxT forecast.
Guidance shifts the CAD wedge north Sunday night. However, it
is wise to hold onto an onshore flow and lower temperatures
longer than guidance, so gradual improvement is given for
Low pressure currently over Oklahoma will continue to drift
northeast reaching the the Midwest tonight before dissipating
over the Great Lakes under a northern stream ridge Sunday night.
A second low currently along the California coast will reach
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 with slight
chance for thunder for the LWX CWA Monday. Possibly a break in
action, so Monday night was kept low at this time.
.LONG TERM /TUESDAY THROUGH FRIDAY/...
Guidance is not in great agreement regarding the weather systems
in our region through the long term. However, most models agree
that we will start out in the warm sector on Tuesday. Tuesday
morning, the GFS has low pressure near Lake Erie, while the EC
has the low furthe southwest over southern Indiana. GFS sends
the low east across the St. Lawrence Valley and brings a cold
front south in the evening, while the EC solution is slower and
weaker with the low, with any frontal passage delayed until at
least early Wednesday. This system will bring a threat of
showers and thunderstorms with, with notable instablity progged
across our region in the warm sector. By late Wednesday, both
models have the front south of, with high pressure from Canada
pushing cooler and drier air into the region. The remainder of
the week appears to be in the cool sector north of the front.
While Thursday starts out dry, by day`s end models bring another
low pressure wave eastward into the region, with an increasing
risk of rain by Thursday night and Friday. This system appears
less likely to bring any thunder with it as current guidance
generally keeps the warm sector away from us, resulting in a
cool and rainy end of March.
.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
VFR under high pressure and southerly flow through today.
Backdoor cold front shifts west across the DC metros tonight
with onshore flow 10 to 15 knots through Sunday. Drizzle and IFR
conds eventually develop and spread east to west late tonight
Southwesterly flow from low pressure to the west/north Monday
brings rain showers to the DC metros Monday.
Thunderstorms are the main concern Tuesday. This concern will
end at night and Wednesday looks VFR with some gusty NW winds
likely behind a cold front.
Southerly flow 10 to 15 knots today interrupted by a backdoor
cold front tonight. Onshore flow expected Sunday into Monday
before shifting south.
Generally sub-SCA SWly flow prevails Monday.
Thunderstorms are possible Tuesday. SCA possible behind a cold
MARINE...Small Craft Advisory until 6 AM EDT early this morning for