Scientific Forecaster Discussion
fxus66 ksew 230429
Area forecast discussion
National Weather Service Seattle Washington
929 PM PDT Sat Apr 22 2017
Synopsis...showery weather will continue for the next several
days as a series of weather systems move through.
Short term...showers are tapering this evening as a short wave
exits the area and with the loss of daytime heating. There has
been a train echo of sorts from south of Seattle northeast into
Issaquah for the last couple of hours. The hrrr shows this
shifting into the Cascades and then fading away in the next hour
or two and recent radar trends seem to support this idea.
Otherwise, isolated to scattered showers will be mostly confined
to the coast and mountains for the rest of tonight with a
generally dry night elsewhere.
Another short wave upper trough will push into the area on Sunday.
This will combine with daytime heating to create increasing
showers through the day. It will not be as unstable as today and
the thunder threat looks negligible. A somewhat more organized
weather system will move onshore to the south on Monday. The bulk
of the moisture with this system will stay south of the area but
the south part of the forecast area will get a glancing blow of
precipitation. It will also still be slightly unstable with an
upper low overhead and some showers will probably bubble up with
It looks like showers will end Monday evening for a dry period
through at least the first half of Tuesday. Another frontal
system will reach the area Tuesday with rain spreading onshore.
The coast will probably be wet in the afternoon but rain could
hold off until late in the day for the interior. Schneider
Long term...previous discussion...the various ensemble means for
each of the models are in line with their operational solutions.
Model consistency and continuity from about Thursday Onward has
generally decreased over the past 24 hrs. The GFS shows a rather
dirty ridge between systems later Friday with no real improvement
in conditions through day 10 (cool and wet through the period).
The European model (ecmwf) is now more aggressive with ridging that develops along
135w on Friday then amplifies somewhat and shifts eastward into
the Pacific northwest next weekend for drying and warming. Probability of precipitation
were lowered toward the tail end of the forecast period and sky
cover was decreased somewhat, in line with the multi-model
Aviation...an upper trough will spread into western Washington on
Sunday, bringing a resurgence of fairly widespread rain by late
morning. The air mass will become even more moist on Sunday
morning, so cigs on Sunday will mainly be in the 020-035 range.
The air mass will be a bit unstable. Moderate southwest flow aloft
will prevail for the next 24 hours.
Ksea...air mass will become increasingly moist through Sunday
morning, so a gradual downward trend in cigs is expected. Cigs in
the 020-030 range are expected to prevail on Sunday morning.
Numerous light to moderate rain showers are expected to at the
terminal from late Sunday morning through Sunday afternoon.
Southerly winds will prevail for the next 24 hours. Haner
Marine...southerly winds will ease for the rest of tonight. A
weak surface trough will move NE across the area on Sunday. A 1002
mb surface low will move eastward onto the far South Washington
coast or far north Oregon coast on Mon morning. A front will move
NE across the waters on Tue, preceded by southerly offshore flow
then followed by southerly onshore flow. Haner
Pz...Small Craft Advisory until 3 am PDT Sunday for coastal waters
from Cape Flattery to James Island 10 to 60 nm-coastal
waters from Cape Flattery to James Island out 10 nm-coastal
waters from James Island to Point Grenville 10 to 60 nm-
coastal waters from James Island to Point Grenville out 10
nm-coastal waters from Point Grenville to Cape Shoalwater
10 to 60 nm-coastal waters from Point Grenville to Cape
Shoalwater out 10 nm-East Entrance U.S. Waters Strait of
Juan de Fuca-Puget Sound and Hood Canal.
Small Craft Advisory for rough bar until 8 am PDT Sunday for
Grays Harbor bar.
Small Craft Advisory until 5 am PDT Sunday for Admiralty Inlet-
northern inland waters including the San Juan Islands.
Small Craft Advisory until midnight PDT tonight for West
Entrance U.S. Waters Strait of Juan de Fuca.