Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
910 PM PDT Sat Oct 25 2014
Synopsis...a deep low will reach the coast late this afternoon and
then fill as it moves northeast. Rain and very windy conditions will
occur this evening over western Washington. Sunday and Monday will
be showery. Another weather system will arrive Tuesday. Wet and
breezy weather is likely at times through the end of the week.
Short term...a deep surface low has been tracking northeast through
western Washington this evening. Southerly gradients behind the low
are probably currently peaking and are strong enough to support at
least spotty high wind. Warnings are in effect for central and south
parts of the interior along with the coast for strong west winds. In
addition...wind advisories are up for the north interior where
gradients are expected to be not quite as strong. Winds should begin
subsiding late this evening and continue slowly easing after
Rain has mostly changed to showers this evening as the frontal
system moves inland. Snow levels will drop to 4500-5000 feet
tonight. Spots above 5000 feet in the Cascades like Paradise on
Mount Rainier could pick up at least a few inches of snow by Sunday
Showers will linger Sunday...then mostly end Sunday night as high
pressure aloft builds overhead. After a dry start to Monday...rain
should develop at the coast...then spread inland late in the day as
the next frontal system approaches.
Most of the rain and wind with this system will occur Monday night.
A 980 mb surface low will move inland north of Vancouver Island
early Tuesday morning. This is a typical southeast sucker wind
pattern...windy for the coast and north interior. Wind Advisory
strength winds for these areas look like a good bet and marginal
high wind is possible but it is too far out to worry about that for
now. Rain will change to showers Tuesday behind the front with
easing winds. Schneider
Long term...previous discussion...Wednesday appears to be a mostly
cloudy day with scattered showers. Another organized system arrives
Thursday. At this point the GFS and Euro diverge with the Euro
staying wet and the GFS turning showery. Not confident on any
details but the forecast will stay moist into the weekend. Burke
Hydrology...the Skokomish River is rising again in response to
heavy rain today and tonight. It is possible the river will get
close to flood stage tonight. For now the forecast takes the stage
at Potlatch to between 15.5 and 16 feet. Flood stage is 16.5 feet.
A break in the rain will allow the skokomish to recede river Monday.
Another front Monday night and Tuesday will bring 2-3 inches of rain
to the skokomish basin. Will need to keep a watch on this but the
current forecast keeps the river below flood stage.
Otherwise...flooding on other rivers is unlikely over the next 7
Aviation...a 991 mb surface low over southern b.C. Will continue
moving NE tonight while higher pressure builds inland over West Washington.
Very strong west-northwest onshore flow will gradually weaken...allowing
strong surface winds to diminish overnight. An upper level trough
over the area will move east tonight...but another upper level
shortwave trough will move down the b.C. Coast and over West Washington Sunday.
This will keep showers going over the area through this weekend.
Conditions will be a mix of VFR and MVFR...with MVFR ceilings most
likely around Puget Sound sound and around showers.
Ksea...as of 04z strong SW surface winds have probably peaked this
evening and will gradually diminish the rest of tonight. The pdx-bli
pressure gradient has begun to weaken. Onshore flow will keep
showers going over the area through Sunday. This will keep ceilings a
mix of MVFR and VFR from 1000-4000 feet. Kam
Marine...a 991 mb surface low over southern b.C. Will continue
moving NE tonight...while higher pressure builds inland over West Washington.
Extremely strong west-northwest onshore is producing gales over all
waters...which will peak in the next few hours...then gradually
diminish overnight. The hrrr model has been handling the pattern
pretty well. Even though high pressure is building inland
tonight...a surface trough will remain over West Washington through much of
Sunday. An offshore surface ridge will finally move over the area
Sunday night and Monday. Models remain on track with the next
frontal system approaching the area Monday...then reaching the coast
Monday night. It looks like a round of more typical gales for the
coast and northern interior waters. After a Post-frontal trough on
Tuesday...another surface ridge will build over the area middle next
Washington...High Wind Warning coast...southwest interior...Seattle/Tacoma
Wind Advisory northwest interior and east Puget Sound sound lowlands.
Pz...Gale Warning all waters.
Small Craft Advisory for rough bar conditions Grays Harbor.
You can see an illustrated version of this forecast discussion at