Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
910 am PDT Monday Sep 1 2014
Synopsis...weak high pressure aloft will prevail over the area
today for a dry day. A front will bring a little rain on Tuesday.
High pressure aloft will rebuild over the area for the rest of the
week for dry and warmer weather.
Short term...northwest flow aloft will prevail today for a
generally dry day. A weak decaying front could bring a few sprinkles
to the coast but that should be about it. Clouds are currently a
little more extensive that previously expected but the trend towards
a partly sunny day for the interior still looks good.
A fairly vigorous upper trough and associated cold front will move
through the area later Tuesday. This system looks like it will bring
a little rain to all areas with a Puget Sound sound convergence zone
lingering into Tuesday night. The highest parts of the mountains
could see a little snow Tuesday night as snow levels drop to around
6500 feet...the first sign that fall is not far away.
Drier northerly flow aloft will quickly develop Tuesday night and
Wednesday as high pressure aloft builds offshore. This will bring a
return to dry weather with decreasing clouds. Schneider
Long term...an upper ridge over the northeast Pacific will keep the
weather dry for the remainder of the week with plenty of sunshine.
There will even be a bit of a thermal trough along the coast for
offshore flow. This should allow highs to warm to near 80 by Friday
or Saturday. The upper ridge looks like it will break down around
Sunday with a return to onshore flow...increased cloudiness...and
highs cooling back to near normal. Schneider
Aviation...light northwest flow aloft over the region will become westerly
and strengthen Tuesday as an upper level trough approaches
Washington from the north. The moist and stable air mass this
morning will become weakly unstable this afternoon with a slight
chance of showers...mainly north of Seattle this afternoon. Ceilings
over the central sound have filled in and lowered somewhat over the
last hour or so to MVFR levels with a few spots a bit lower. Expect
general conditions to improve with ceilings lifting to VFR levels
around 18z. Increasing middle and high clouds will likely keep skies
from completely scattering out...but expect VFR conditions to
persist through the evening hours. Increasing showers Tuesday with
the approaching upper level trough.
Ksea...S wind to 4-7 knots after 19z/12 PM then switching to the north
after 00z/5 PM this afternoon. IFR ceilings this morning will become
MVFR over the next hour then VFR by 18z/11 am. VFR conditions will
prevail through this evening with a broken-overcast 4-5k feet deck...then fill
and lower early Tuesday morning to MVFR levels. There remains a
slight chance of a shower through tonight. Increasing showers
Marine...a surface trough will dissipate over the coastal waters
today. Southerly winds ahead of the trough should remain below 20 knots over
the coastal waters...with light southerly wind over the inland waters.
Solid onshore flow through the Strait will develop tonight as
gradients tighten overnight followed by another system that will
bring another bout of strong onshore flow Tuesday night. Gradients
ease on Wednesday then return to a typical late Summer pattern
through the rest of the week.
Pz...Small Craft Advisory central and eastern Strait of Juan Delaware fuca.
.Gale watch central and eastern Strait of Juan Delaware fuca Tuesday
afternoon through late Tuesday night.
You can see an illustrated version of this forecast discussion at