Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 201430

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
930 AM EST Mon Feb 20 2017

High pressure will build from the west today. Cooler air will
seep south tonight into Tuesday. A weak disturbance will cross
the area Tuesday night into Wednesday. High pressure will be
located off the southeast coast of the United States for the
second half of the week.


Upper-level ridge will build overhead today while high pressure
builds over eastern Canada into New England. A north to
northeast flow will develop overhead ahead of the building high.
The northerly component to the surface wind will allow for
cooler conditions compared to recent days...but max temps will
still be well above climo. High clouds rotating around the
periphery of the upper-level ridge will filter sunshine at

Flow turns northeast ahead of the ridge axis tonight, which will
allow marine air to move inland and overspread the area.
Meanwhile, flow aloft will be southwest, making for an
overrunning setup. Have increased clouds, first in the mountains
(where the low-level flow will be upslope) but eventually
areawide. Am focusing more on clouds than fog. Further, these
clouds don`t look partularly low. In spite of the cloudcover,
advection will bring temperatures down into the 30s.


A 500 mb full-latitude shortwave axis will approach the area
Tuesday into Wednesday. However, it appears as though the
northern and southern streams will split-- the northern vortmax
breaks down the ridge in the northeastern United States while
the southern vort gets left behind along the Gulf Coast. The
impact to the Mid Atlantic a bit muddled. Certainly, this will
be a cloudy period, and can`t rule out scattered showers
beginning Tuesday night. However, am having difficulty
believing it will be as wet as current guidance runs
suggesting...or for as long. Did increase clouds/PoPs on
Wednesday, but am still holding onto the thought that there
will be clearing in the wake of the vortmax Wednesday afternoon.

Tuesday will be the coolest artifact of clouds and
onshore flow. However, once the ridge axis pushes east of the
area, there is sufficient warmth ready to return.


Shortwave-ridge builds over the area Thu and Fri. It will be
very warm especially Thu with highs in the 70s. Some locations
may reach mid to upper 70s.

Deep low pressure moving across the Great Lks Fri night and Sat
will push a cdfnt through the area Sat morning with showers and
t-storms likely some of which could be strong to severe and pose
a risk of damaging winds given fast 0-6km mean flow of 45-50kt
and weak instability. Cooler wx returns for early next week.


VFR for the valid TAF period. As onshore flow commences
tonight, low clouds will increase...first in the mountains but
eventually everywhere. The greatest probability is that
conditions remain VFR. There is a lower chance that ceilings dip
below 3000 ft.

Ceiling lift but remain broken Tuesday. Then a disturbance adds
a shower chance Tuesday night into Wednesday morning. If there
is an opportunity for flight restrictions, this would be the
time frame that it would happen.

No significant wx expected on Thu. Strong cdfnt fcst to cross the
area Sat morning with t-storms possible.


High pressure will build over the waters through tomorrow,
resulting in relatively light winds-- 10 kt or less. Winds will
become north today, northeast then east tonight, and eventually
south by Tuesday or Tuesday night. A passing disturbance may
provide a shower chance Tuesday night into Wednesday.

Strong cold front will move through the waters Sat morning with
showers and t-storms likely, some of which could be severe and
produce strong damaging winds. Gale force winds are also likely


Record high minimums were set yesterday at IAD and BWI. See
RERs for more details. More record high mins are likely later
this week especially on Fri with possible record highs on Thursday.




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