Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
830 am PDT Wednesday may 27 2015
Synopsis...low level onshore flow will weaken slightly over the
next couple of days...allowing for warmer and sunnier weather. An
upper low will bring some showers and cooler weather early next week.
Short term...an upper low over eastern Washington will slowly pull
away from the area with weak high pressure aloft building over
western Washington today and Thursday. At the same time...low level
onshore flow will weaken a bit and turn more northerly. The upshot
is low clouds over the area this morning should scatter this
afternoon and highs will warm into the 70s. There should be less low
clouds Thursday morning with highs in the 70s to lower 80s.
500 mb heights will begin to fall across the area Friday as an upper
low over British Columbia sags south towards western Washington.
This will also cause low level onshore flow to increase again. That
said...it does not look like these changes will have much affect on
the weather. Low level moisture will be limited for another mostly
sunny day. 850 mb temperatures actually warm slightly and highs
should once again be in the 70s to lower 80s.
There will be enough instability over the Cascades for a chance of
afternoon and evening showers for the next few days. Schneider
Long term...previous discussion...500 mb heights will slowly lower
this weekend with a bit of an increase in low level onshore flow.
This will cause highs to cool slightly but temperatures will remain
An upper low off the far northern California coast will either move into
Oregon or Washington on Monday. Not surprisingly...the models were not in
very good agreement with how this will unfold. The general idea
was that moisture coming up from the south will start to impact
the County Warning Area on Monday as the upper low approaches. The upper low will
remain in the vicinity for a continued chance of showers on
Tuesday. High temperatures will cool to near normal by Tuesday as
clouds and onshore flow increase. Schneider/05
Aviation...northerly flow aloft. Light onshore flow. The air is
moist with areas of marine stratus that for the most part will lift
and burn off into the afternoon hours.
Ksea...the morning clouds should scatter out midday.
Marine...high pressure will remain offshore with lower pressure
inland through the week. Onshore gradients increase Friday afternoon
and evening for possible Small Craft Advisory strength west winds in
You can see an illustrated version of this forecast discussion at