Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
346 PM PDT Thursday Sep 18 2014
Synopsis...a weak disturbance will move across the area later
tonight through early Friday morning. High pressure aloft will
begin building over the region on Friday. Look for high pressure
aloft and low level offshore flow to prevail this weekend for well
above normal daytime temperatures.
zonal flow aloft will prevail across the area tonight. A weak
short wave trough embedded in this flow will result in some showers
across mainly the northern part of the County Warning Area. The showers will
persist into Friday morning.
An upper ridge will begin building over the region on Friday. The
ridge will amplify this weekend. This combined with low level
offshore flow will result in well above normal daytime temperatures.
Some places could end up tying or breaking daily records.
the upper ridge axis will move over the intermountain west on Monday
and this will allow a weakening occluded front to approach the
coast. This front will likely dissipate as it moves onshore. The
main impact will be cooler and cloudier weather Monday and Tuesday.
Beyond Tuesday...a stronger system will impact the Pacific northwest
during the latter part of the extended period...resulting in below
normal daytime temperatures and breezy conditions. This system is
expected to remain off the coast through Thursday.
Aviation...the flow aloft is westerly as an upper level trough
pushes into eastern Washington. A weak warm front will spread spotty light
rain to the area tonight. The air mass is moist and stable. Ceilings
will lower tonight with MVFR conditions likely. A cold front will
cross through western Washington Friday morning for a few more showers. 33
Ksea...ceilings likely remaining in MVFR range tonight with spotty light
precipitation in the vicinity. Surface winds will remain light southerly. 33
Marine...surface winds will be mainly light across the waters
tonight with weak high pressure along the coast. However...a westerly
onshore push will bring a few hours of Small Craft Advisory winds
through the central and east Strait of Juan Delaware fuca this evening. A
weak cold front will cross through western Washington on Friday. Winds will
flip to offshore Friday night through Sat as a thermally induced trough
of low pressure forms along the coast. The winds will then turn
southerly on sun as a surface trough develops over the offshore
waters. This trough will cross through the coastal waters on Monday. 33
Pz...Small Craft Advisory in effect until 2 am Friday for the
central and eastern Strait of Juan Delaware fuca.
You can see an illustrated version of this forecast discussion at