Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
900 am PDT Wednesday Apr 1 2015
Synopsis...an upper trough will bring showers and cool weather
today. Showers will diminish Thursday as weak high pressure builds
over the area. A frontal system will affect the area on Friday. An
upper low will maintain a chance of showers through the weekend.
Short term...an upper level trough will maintain cool and showery
weather across western Washington today. The air mass is moist and unstable
with a chance of thunderstorms once again. The infrared satellite
shows a line of showers over the coastal waters associated with the
trough axis. These showers will affect the coast this morning and
the interior this afternoon. The freezing level on the kuil sounding
this morning is 3500 feet so low elevation snow showers are expected
in the Cascades and Olympics. Heavy snow showers from the
convergence zone have ended across the west slopes of the Cascades
in King County this morning. However the passes could still see a
couple inches of new snow today.
The air mass will dry out and stabilize on Thursday as a weak upper
level ridge shifts inland. This is a dirty ridge and skies will
likely remain mostly cloudy. Our next cold front will reach the
coast early Friday morning...with rain spreading into the interior
by the afternoon. 33
Long term...previous discussion...a cool and showery upper trough
will be over the area Saturday through Monday. There is general
agreement in the models that an upper ridge will move overhead on
Tuesday for drier and warmer weather. Schneider
Aviation...a shortwave upper trough over western Washington today
will move east of the Cascades tonight as an upper ridge builds just
offshore. Moist onshore flow will continue at low levels. The air
mass is unstable today with showers increasing into the afternoon
and a chance of thunderstorms. Showers may linger tonight in the
Puget Sound sound convergence zone and along the west slopes of the
Ksea...showers increasing into the afternoon...southerly winds
should become variable in a pscz later this afternoon and evening.
Watch the radar and lightning detection this afternoon as there is a
chance of thunderstorms in unstable air.
Marine...a trough will move through western Washington today. Onshore flow.
Westerlies will increase later this afternoon and evening in the
Strait. Winds will ease later tonight in the Strait as high pressure
builds into the area. Puget Sound sound should see a pscz develop this
afternoon and evening.
A cold front will move through the area Friday. It should bring
Small Craft Advisory southerlies to the coastal waters...entrances
to the Strait...Admiralty Inlet...and northern inland waters. A low
over the offshore waters of British Columbia Saturday will move
southeast to the Washington offshore waters on Sunday. The exact
path of the low is fairly uncertain...but it does not look like
there will be significant winds associated with it.
Pz...Small Craft Advisory central and east Strait of Juan Delaware
Small Craft Advisory Grays Harbor for rough bar.
You can see an illustrated version of this forecast discussion at