Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
515 am PDT Friday may 22 2015
Update...showers have been increasing the last couple of hours and
and drifting west from the Cascades into The Lowlands from about
Everett southward. The hrrr model seems to have the best handle on
this activity and suggests there will be isolated showers this
morning over central and south Puget Sound sound and the southwest
interior before they mostly Peter out and become confined to the
mountains in the afternoon. The forecast was updated to account for
these changes. The remainder of the forecast remains on track and
was not changed. Schneider
Synopsis...skies will be mostly cloudy today and Saturday with
moderate to strong onshore flow. Onshore flow will continue next
week for a pattern of morning clouds and partial afternoon sunshine
each day. Weak low pressure aloft will bring a chance of showers...
mainly over the mountains afternoon and evenings.
Short term...low level onshore flow will be stronger today compared
to yesterday. Low clouds have been spreading into the interior early
this morning and should cover most of The Lowlands in a few hours.
There will probably not be much clearing today even in the afternoon
although there could be a few sun breaks. Highs will cool into the
60s. There will be a chance of mainly mountain shower and
thunderstorms in the afternoon where the air mass is most unstable.
Saturday and Sunday look like relative repeats of today with
moderate to strong low level onshore flow continuing and somewhat
unstable air over the mountains for a chance of afternoon and
evening showers and thunderstorms. Schneider
Long term...the general pattern will change very little Monday
through Thursday. A weak upper trough will be over the Pacific
northwest with low level onshore flow. There should be morning
clouds and some afternoon sunshine each day with a chance of
showers... mainly over the mountains afternoon and evening hours.
Highs will be near or slightly above normal. Schneider
Aviation...an upper low over the central coast of British Columbia
will remain stationary through today keeping the flow aloft light.
Low level onshore flow continuing today. Air mass destabilizing over
the Cascades this afternoon.
Satellite imagery shows stratus along the coast...down the Strait
into the San Juans and extending inland to the central Puget Sound sound
at 10z. Ceilings are below 1000 feet with the stratus. Expect all of
the interior lowlands except the Cascade foothills to be covered in
stratus by 14z. Onshore flow continuing today keeping the stratus
intact over The Lowlands well into the afternoon. Ceilings will
slowly lift into the 1000-2000 foot range by late morning and to
near 3000 feet by late afternoon over the interior. Ceilings along
the coast will stay in the 1000-2000 foot range. The best chances
for some clearing will be near kbli. With the onshore flow pattern
continuing into Saturday morning stratus will remain over the
interior with ceilings lowering back down into the 1000-2000 foot
range tonight. There is a chance of more thunderstorm activity again
over the Cascades tonight with most of the activity expected to stay
near the crest.
Ksea...ceilings below 1000 feet until late morning lifting to near
3000 feet by late afternoon. Southerly winds 6 to 10 knots. Felton
Marine...persistent high pressure offshore with lower pressure inland will
result in continued onshore flow of varying strength through Tuesday.
Another round of gale force winds are expected in the central and
eastern Strait tonight. Expect Small Craft Advisory winds late in
the day Saturday through the first part of next week for the central
and eastern Strait with the low level onshore flow continuing. Small
Craft Advisory winds are also forecast for the outer coastal waters
today. With the gradient weakening slightly later today the winds in
the outer waters will fall below 20 knots. Winds over the remainder
of the waters will remain below 20 knots the next few days. Felton
Pz...Gale Warning central and East Entrance Strait of Juan Delaware fuca.
Small Craft Advisory outer coastal waters.