Weather Service Report


316 
FXUS66 KSEW 310420
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
920 PM PDT TUE AUG 30 2016

.SYNOPSIS...A cold front will slowly move inland tonight and
Wednesday for a little rain. An upper level trough will maintain
cooler weather with a chance of showers from Thursday into early
next week.

&&

.SHORT TERM...Longwave trough out around 135W this evening, with
southerly flow aloft over western Washington. A slow-moving north-
south oriented band of clouds and rain is located along and just
off the coast right now, in association with a cold front. A
shortwave will eject from the trough tonight, this will shoving
the cold frontal clouds and rain onto the Olympic Peninsula by
sunrise Wednesday. The rain will continue to spread inland,
reaching the I-5 corridor around mid-day. The rain will weaken as
it moves inland, but it should bring the first measurable rain to
the I-5 corridor since Aug. 3-8, depending on location.

Less widespread shower activity will linger on Wednesday night,
but the front will remain over the area. Showers and rain will
pick up again on Thursday, as a frontal wave spreads in from the
SW and an upper low swoops in from the northwest.

The upper low and its attendant cold pool aloft will pass
directly across western Washington on Thursday night and Friday
morning, continuing abundant shower activity. As the upper low
starts to exit late Friday, showers will become more focused over
the mountains in the Puget Sound Convergence Zone, while tapering
off elsewhere. Haner

.LONG TERM...From Previous Discussion: A large scale upper trough
will remain over the Pacific Northwest this weekend for a chance
of showers. Weak high pressure aloft will dry things out on Monday
and Tuesday but some moisture could still spill into the area from
the northwest. Models have not been very consistent with the
details. Schneider

&&

.AVIATION...There is an upper level trough offshore with
southwesterly flow aloft over the Pacific Northwest. A weakening
cold front will be moving through the area Wednesday.

Just some high clouds over the interior of Western Washington this
evening with lower ceilings on the coast. Ceilings lowering over the
interior Wednesday morning down to the 3000-4000 foot range with
areas of light rain. Ceilings along the coast a little lower 1500-
2500 feet. Some improvement late in the day.  

KSEA...Just some mid/high level clouds into the early morning
hours. Ceilings lowering to near 3500 feet mid to late morning.
There wont be a good frontal passage so improvement later in the day
will be slow to develop. Southerly winds 5 to 10 knots. Felton 

&&

.MARINE...A cold front just offshore will slowly move through the 
coastal waters tonight then move inland on Wednesday. A small craft
advisory is in effect for the coastal waters tonight but the inland
waters are only likely to see southerly winds up to about 15kt.
The next front should arrive Thursday afternoon and night and there
is a better chance of small craft advisory strength winds--at least
for the coastal waters. Onshore flow will develop on Friday and
continue into the weekend. Felton

&&

.SEW Watches/Warnings/Advisories...
WA...None.
PZ...Small Craft Advisory coastal waters.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.weather.gov/seattle/gafd/latest_webafd.html

Return to Home page


Western Regional Climate Center, wrcc@dri.edu