Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 190900

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
400 AM EST Sun Feb 19 2017

A weakening area of low pressure will move into the Atlantic
this morning. High pressure will return this afternoon and
tonight. A backdoor cold front will enter the area Monday into
Tuesday. Another disturbance will cross the area early Wednesday.
High pressure will be located off the southeast coast of the
United States towards the end of the week.


Through the 1 and 2 o`clock hours and continuing past 3am, an
east-west arc of precipitation can been seen on radar across
the forecast area from near Elkins across metro Washington DC.
However, clouds are mainly mid deck, and the associated forcing
is soley a packet of vorticity around 500 mb. Have not seen
visibility restrictions anywhere, making the radar returns
sprinkles. Have worded forecast as such. RAP and HRRR runs
through the night have been fairly consistent in drying the
precip up before sunrise. Grids follow suit.

Heights rise during the daylight hours as an axis of high
pressure shifts east today. As a shortwave crosses New England
winds become northwesterly. Mixing looks fairly decent, with
mean layer gusts in the mid teens (kts). That should offset any
cold advection. Guidance temperatures look comparable to
yesterday. Will employ a bias-correction to attempt to get
cooler readings along the shoreline of the Chesapeake Bay.


From tonight through Monday night, a deep layer ridge axis will
translate east, cresting over the East Coast of the United
States. However, another lobe of vorticity rotates around the
trough axis over the Canadian Maritimes, veering winds
north/northeast and sending a backdoor cold front toward the Mid
Atlantic. The actual cool-down has been challenging to
forecast-- placement, timing, and intensity; latest guidance is
focusing more on late Monday afternoon/Monday night (northeast
Maryland) into Tuesday (down to the Potomac River). Will follow
that lead at this time. Aside from temperatures concerns, the
period looks mostly sunny and dry. For that matter, the period
will also be mild for late February, just not as warm as

Meanwhile, a deep-latitude, sharply amplified shortwave will be
crossing the country. It will be arriving in the Appalachians
Tuesday night. It`s hard to discern if there will be any surface
reflection. That once again makes precipitation prospects
questionable. Have confined PoPs Tuesday afternoon to a slight
chance northwest of Charlottesville-DC-Baltimore and lowered
PoPs Tuesday night to 20-30 percent areawide. Clouds will be
increasing though, beginning on Tuesday.


Wednesday through the first part of the weekend will continue
the unseasonably warm weather. On Wednesday high pressure
settles off the Southeast coast and remains there through the
early Saturday. Generally dry weather will be the rule but
models do show an area of low pressure moving across the Great
Lakes region early Thursday that could help draw up sufficient
moisture for a few showers then. Meanwhile low pressure develops
in the southern Plains Wed and deepens as it moves northeast
into the Great Lakes region Friday night. A cold front will
extend from this low that will cross the region on Saturday.
Ahead of the front will see an decent plume of moisture.
Depending on the timing of the cold front on Saturday...there
could be sufficient instability around to fire off thunderstorms
along the front as it crosses the region. High pressure builds
in Saturday night.


VFR flight conditions will prevail across the terminals. There
are a few sprinkles at DC metro TAFs, but these should cease by
sunrise. In the wake of this disturbance, northwest winds will
increase, with some gusts approaching 20 kt at inland northern
terminals (IAD-MRB).

Winds will become more northern Monday and northeast Tuesday. Do
not anticipate gusty winds, though. Clouds will be sparse
through Monday night, when high deck clouds will thicken.

Wednesday and Thursday...surface high pressure will be off the
southeast coast. Low pressure passing to the north will help
draw in clouds on Thursday...with MVFR ceilings possible in
scattered showers.


Water temperatures remain in the lower 40s. Gradient winds will
increase today in the wake of an upper disturbance. However, air
temperatures over land will be in the 60s to near 70. Even after
modification due to the marine environment, expect a rather
sharp inversion, making it challenging for gusts to mix to the
surface. If it were to happen, it would be in a nearshore
environment. Left the Small Craft Advisory today for the upper
tidal Potomac and Baltimore Harbor, which fits the confluence
between 20 kt winds aloft and a narrow waterway. Otherwise,
Advisory has been cancelled.

High pressure builds tonight into Tuesday, making for light
winds. The direction will be veering from northwest today to
north Monday and eventually northeast Tuesday as a subtle,
backdoor cold front settles across the waters.

High pressure settles off the southeast coast on Wednesday and
continues through the end of the week. Winds expected to remain
below 15 kts during the day.


Very warm temperatures will persist today. Here is the list of
records at the climate locations.

                      Sunday          Sunday
Site              Record high min   Record high
Washington/Reagan    52 in 1981      74 in 1939
Baltimore/BWI        47 in 1976      72 in 1997
Washington/Dulles    46 in 1981      71 in 1997


MARINE...Small Craft Advisory from 10 AM this morning to 6 PM EST this
     evening for ANZ535-538.


CLIMATE...RCM/SMZ is the U.S. government's official web portal to all federal, state and local government web resources and services.