Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 280345

Area Forecast Discussion
National Weather Service Seattle WA
845 PM PDT Thu Oct 27 2016

.SYNOPSIS...An upper level trough lifting into British Columbia will
keep showers over the area this evening and into tonight. Weak upper
level ridging and high surface pressure east of the Cascades will
help conditions dry on Friday, especially over the interior. For the
weekend and early next week, a series of disturbances will keep
unsettled weather over the region, with brief periods of dry weather
between systems.


.SHORT TERM...An upper level trough axis will pass over the area
tonight...keeping showers both in the forecast and on the radar.
This feature is expected to exit the area by early Friday morning
with showers tapering off accordingly.

Now for some good news...model solutions still look good for a weak
upper level ridge to push west from Eastern Washington resulting in
dry conditions from the late morning and through the afternoon and
evening. Interior locations may even catch a fleeting glimpse of
what science textbooks refer to as the sun. the
waterlogged populace of Western Washington knows...this will be
short lived as moisture associated with an upper level low out over
the Pacific will push into the area during the overnight period late
Friday night or early Saturday morning bringing a return to showers
to the area off and on through the day Saturday. Looks like there
will be a bit of a reloading moment that will bring a pause in the
precipitation late Saturday night into Sunday morning...with another
round of showers Sunday afternoon and evening as the aforementioned
upper level low finally pushes on shore to close out the weekend.

Inherited forecast looks to cover all of the no updates
are expected this evening.  SMR

.LONG TERM...From the 325 PM PDT discussion...Medium range models
continue to show split flow dominating along the west coast of the
US from Sunday through the middle of next week. This will allow a
series of weak systems to brush the area, bringing periods of rain
with drier weather between. The challenge will be refining the
timing, location and duration of the rain as well the drier weather.
The first upper level trough moving into Oregon on Sunday continues
to look like it will remain mainly to the south of the area with
Western Washington seeing clouds and the best bet for rain south of
Seattle. A weak system embedded in the northern stream of the split
flow will clip the area Monday, resulting in a chance of rain Monday
into early Tuesday. An upper level ridge and low level offshore flow
Tuesday will result in the driest weather in the extended, followed
by a shift in the large scale pattern that will bring more
consolidated flow into the Western Washington and a return to more
active weather.


.AVIATION...A weak upper trough embedded in moderate southwest flow
aloft will pass western Washington this evening. Showers have been
enhanced as the trough swings by, but they will fade late tonight
after the upper trough passes. Surface flow is moderate southerly
tonight; it will ease Friday.

Conditions are mostly VFR with local MVFR ceilings within shower
activity. On Friday, a brief period of upper ridging will build into
the area, and drying low-level easterly flow will strengthen during
the day. This will lead to more substantial thinning and scattering
of low-mid level cloud layers on Friday.

KSEA...The frequency of passing showers will peak 03z-08z tonight.
Ceilings will mostly be 4k-6k ft, but could drop briefly into the 2k-
3k ft range during showers. Showers will dissipate overnight. Some
improvement Friday. Southerly wind 4-8 KT. CHB


.MARINE...A weak 1008 MB low will move north inside 130W Friday,
further weakening over the offshore waters Friday night and
Saturday. A small craft advisory is in effect on the coast beginning
late Thursday night and continuing through Friday afternoon. Low
pres will move northeast through the Oregon waters Sunday, then
weaken as it moves northeast through Western Washington Monday. CHB


.HYDROLOGY...River flooding is not anticipated over the next 7


.CLIMATE...The record for October rainfall for Seattle remains
intact at the time of this writing. The current record...8.96
inches...was set in 2003. As of 8 PM PDT this evening...rainfall at
SeaTac sits at 8.93 inches.  With the prospect for showers in the
forecast for tonight as well as for portions of the upcoming
weekend...there are still plenty of opportunities to see the old
record fall. SMR


PZ...Small Craft Advisory coast.



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