Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
353 am PST Tuesday Dec 1 2015
Synopsis...a low pressure system will bring locally heavy
precipitation and gusty winds to the area later today through
tonight. Look for a warm front to approach from the southwest
during the day Wednesday before moving across the region Wednesday
night. A strong cold front will then sweep across the area on
Thursday for windy conditions.
a few light showers lingered over the County Warning Area at this time...otherwise
skies were overcast.
A stronger low pressure system will begin impacting the Pacific
northwest today. This system was still currently well offshore but
the precipitation associated with it should reach the coast later this
morning. The occluded front was oriented nearly parallel to the
flow...thus the precipitation will be slow to spread inland. This means
that much of the interior will remain dry today.
The occluded front and upper level trough will move across the area
tonight for a period of locally heavy precipitation. A Winter Weather
Advisory for snow was issued for the Cascades from Snohomish
County to Lewis County where snowfall amounts of 6 to 11 inches
are likely. The precipitation will likely fall as snow in the passes
during this period due to persistent cold easterly flow. The
exception may be Snoqualmie Pass where the precipitation may change over
to freezing rain or a rain/snow mix early Wednesday.
It looks like there will be a lull or break on Wednesday between
systems. Steady rain should develop in the afternoon and then
overspread the County Warning Area Wednesday night ahead of a warm front. The cold front
is anticipated to sweep across the region on Thursday. It looks like
Thursday will be windy...with speeds likely reaching advisory criterion
in the favored areas /coast and northwest interior/. However...
there continued to be some disagreement in the track of the
surface low. A farther eastward track would result in the
potential for high winds. Noticed that the 0600 UTC GFS solution
was farther west with the track of the low than its previous
run...or was now closer to the European model (ecmwf) solution.
a wet and active pattern will continue over the Pacific northwest
during this period due to a parade of low pressure systems moving
across the region. An atmospheric river may set up over the
area this weekend for the potential of heavy rain on the
southwest slopes of the olympic and north Cascade ranges.
Aviation...a frontal system is dissipating as it moves through the
interior early this morning. Another wave of low pressure will move
north over the offshore waters this morning. A stronger wave
will move through the coastal waters this evening. Moderate southwest
flow aloft. High pressure over eastern Washington combined with
lower pressure offshore will give low level offshore flow.
Despite clouds and -ra at times tonight and again Tuesday
evening...expect ceilings and visibility to remain mainly in the VFR
category through tonight. Albrecht
Ksea...some light showers...remnants of a dissipating front aloft...
will move NE past the terminal early this morning. Then conditions
are expected to be cloudy with ceilings scattered-bkn030 broken-ovc050 through
03z Wednesday. -Ra will increase after 03z as a frontal system associated
with a passing wave of low pressure approaches the area from the
west. Wind will be southeast 5-8 knots today and 7-10 knots tonight. Albrecht
Marine...boaters in western Washington are urged to check weather
conditions frequently over the next several days as we move into a
very active weather pattern. A series of potent waves of low
pressure and strong frontal systems will move through the waters
over the next several days...and confidence in the timing of these
features is moderate at best.
A wave of low pressure and associated front will bring gales to the
coastal waters...the East Entrance to the Strait...and the northern
inland waters through tonight. Small Craft Advisory conditions are
expected over the western and central Strait of Juan Delaware fuca and in
A brief lull between systems is expected on Wednesday. The lull will
be followed by another low pressure wave and front that will likely
produce gales over the coastal waters and the East Entrance to the
Strait Wednesday night and Thursday. Small Craft Advisory conditions can be
expected elsewhere with the Wednesday night and Thursday system.
Some forecast models show a deep 985-990 mb low moving through the
waters late Thursday afternoon or Thursday night. This low may bring gales to
all of the waters...and possibly storm force winds to the coast and
entrances to the Strait.
It appears that more strong fronts bringing widespread gales are
likely again over the weekend.
Wave models show the development of 20 to 25 feet seas from the
southwest over the coastal waters Thursday and Saturday. If seas
develop as expected...many locations on the coast will see periods
of beach erosion. Albrecht
river flooding is not expected through Friday. There is a possibility
that a few rivers may flood this weekend.
Washington...Winter Weather Advisory in effect from 4 PM this afternoon until
4 am Wednesday for Cascades of Snohomish County to Lewis
Pz...gale warnings are in effect until 4 am PST Wednesday for the
coastal waters...East Entrance to the Strait of Juan Delaware fuca...
and the northern inland waters.
Small Craft Advisory in effect until 4 am PST Wednesday for the
Admiralty Inlet and the central/western Strait of Juan Delaware fuca.
Small Craft Advisory in effect for rough bar until 4 am PST
Wednesday for the Grays Harbor bar.
An illustrated version of this forecast discussion can be seen at