Scientific Forecaster Discussion
Fxus66 ksew ddhhmm
Area forecast discussion
National Weather Service Seattle Washington
410 PM PST Monday Nov 30 2015
Synopsis...a weak low pressure system brushing the coastal waters
this afternoon and evening has brought increasing clouds...milder
temperatures and light precipitation to parts of western Washington.
More active weather will return to the region Tuesday as a series of
Pacific storms impacts the Pacific northwest through the weekend.
Short term...the very weak low pressure system and front passing
along the Washington coast has brought increasing clouds as well as
spotty light rain...mainly to the central Washington coast and
Chehalis gap. Precipitation has been pretty limited...amounting to
little more than the odd trace. This will shift north overnight
before giving way to very short lived upper level ridging early
Tuesday morning ahead of the next system expected to begin to move
into the area around midday.
Precipitation with this system will begin to work onto the coast in
the late morning and slowly into the metropolitan area during the evening.
In addition to the precipitation...expect breezy to windy conditions
especially Tuesday night. This system continues to look pretty
benign...with the heaviest precipitation over the mountains. Snow
levels around 2500 feet tonight will rise to around 3000 feet
Tuesday night and 4500 feet Wednesday night. Snow accumulations over
the mountains Tuesday night through Wednesday afternoon could range
from 8 to 12 inches or higher at the volcanos. It is also
significant that cold easterly flow through the passes will persist
through Thursday...keeping cold temperatures and wintery conditions
through the passes despite the rising snow levels.
Long term...the second in the series of Pacific frontal systems
expected this week will reach the area late Wednesday evening as
warm frontal precipitation spreads into western Washington from the
southwest. The cold front will follow Thursday. This system will
bring a bit more precipitation...rising snow levels...and another
bout of breezy to windy conditions Wednesday night. Showers will
linger Friday with a brief break in the form of shortwave ridging
late Friday afternoon or evening ahead of the next system. This
system continues to look like the most organized...and significant
of the bunch...bringing warm sector rain to the area
Saturday...Saturday night...then cold front Sunday. 12z/18z medium
range guidance a bit weaker than previous runs...nonetheless there
remains some potential with this system for flooding on a few
Aviation...clouds with the front moved into western Washington this
afternoon and there is spotty light rain. The offshore flow will help
to dry up this first front but then another will arrive later in the
day on Tuesday. The mountains should remain mostly obscured with the
Switch Back to a moist weather pattern and SW flow aloft.
Ksea...most of the rain with this first front is drying up but we
may see some sprinkles this evening. It will be cloudy tonight and
as a southerly breeze kicks up that should be the end of our stagnant air
and any risk of fog for awhile. There is a better chance of rain
Tuesday night with the next front.
Marine...a classic southeasterly sucker pattern will give gales at
times to the coastal waters and East Entrance of the Strait...and
perhaps the northern waters as well. A first front is moving ashore this
evening. The next one will arrive later Tuesday...and a third will
be Thursday. None of the systems look particularly breezy for the Puget Sound
sound area but should be able to muster a round of gales
elsewhere...the pressure gradients will be too easterly for Puget Sound
sound to give much wind around the metropolitan area.
Hydrology...river flooding is not expected through Friday. Medium
range guidance has been hinting at some flood potential this
weekend...however confidence remains low with respect to timing and
impacts due to model differences. At this time the Skokomish River
remains the most likely to experience flooding...but cannot
completely rule out the threat on other rivers this early.
Pz...Gale Warning in effect for the coastal waters...East Entrance
to the Strait of Juan Delaware fuca...and northern inland waters.
Small craft advisories are in effect for the western/central
Strait of Juan Delaware fuca and the Admiralty Inlet.
Small Craft Advisory for rough bar until 4 am Tuesday for the
Grays Harbor bar.
An illustrated version of this forecast discussion can be seen at