Area Forecast Discussion
Issued by NWS Sterling, VA
FXUS61 KLWX 191515
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1015 AM EST Sun Feb 19 2017
High pressure will build from the west 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.
.NEAR TERM /TODAY/...
Opening mid/upper low is located over eastern NC this morning.
Surface trough has passed through the CWA with northwest winds
established across the CWA. Remaining mid-level forcing is
beginning to move east, evidenced by eroding cloud cover from
the west, and dissipating sprinkles near the Chesapeake Bay. A
handful of observing sites recorded a few hundredths of rain
Expect clouds east of the mountains to continue to dissipate
through midday, although upslope clouds look to persist into
tonight. Added fog/drizzle into early afternoon to high western
facing slopes (W Grant/Pendleton) per traffic cameras.
Heights rise during the daylight hours as an axis of high
pressure shifts east today. Mixing looks fairly decent, which
should result in some wind gusts of 20-25 mph across the
northern half of the area. The mixing also should offset any
cold advection. Guidance temperatures look comparable to
yesterday. Have not made any changes to high temperatures at
this point, which are supported by the 12Z IAD sounding. Will
employ a bias-correction to attempt to get cooler readings
along the shoreline of the Chesapeake Bay.
.SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/...
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.
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
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.
.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
VFR flight conditions will prevail across the terminals. In the
wake of an upper level disturbance, northwest winds will
increase, with some gusts in excess 20 kt possible at inland
northern terminals (IAD, BWI, MRB).
Winds will become more northerly 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
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. Have added a few of the narrower waterways
(northern Bay, Patuxent, middle Potomac) to the SCA, supported
by current gusts around 20 kt near Dahlgren. Northwest winds
should prevent a Bay breeze, maintaining the gustiness along the
western shore. While a pressure surge may continue the winds
after sunset, sounding show a sharp inversion developing, and
have thus not extended the SCA in time.
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.
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 until 6 PM EST this evening for ANZ530-