Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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716
FXUS66 KSEW 281132
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
330 AM PST Mon Nov 28 2016

.SYNOPSIS...Showers will decrease throughout the day today as a
passing front exits the area and an upper ridge builds over Western
Washington...bringing dry weather for Tuesday. Another front will
arrive Wednesday. After a brief dry period Thursday into Friday,
generally wet cool weather looks likely next weekend.

&&

.SHORT TERM...Radar continues to show some shower activity over W WA
this early morning...but trend is definitely downward since the
front moved through last night. Some shortwave disturbances on the
back side of the exiting trough will allow for some showers to
linger today...and that seems to bear out looking at radar trends
upstream. Taking all that into account...not expecting much more in
the way of precip/accumulation for Olympics and Cascades this
morning...but with showers still out there...certainly would not
rule out additional light amounts. Will leave Winter Weather
Advisory headline alone and allow it to expire at 7 AM PST this
morning.

Hark...what light through yonder window breaks...it is an upper
level ridge to the west and it will make its way over the area
Monday night into Tuesday. The light here proves only
metaphorical...because sufficient moisture will remain in place for
cloudy skies...but at this point in the season most would agree that
a break from the rain will be progress enough. That certainly looks
to be the case here. Parting will be such sweet sorrow though...as
verily will the next frontal system start to push inland Tuesday
night bringing the next round of precip. This system...sped up
slightly from model runs 24 hours previous...looks similar to the
system that just passed through the area with two major differences.
First...it appears generally weaker with lesser precip amounts and
second...it breaks apart as it moves eastward over the area. That
said...snow levels look to fall once more to down around the
mountain passes as the front moves through. With lower precip
amounts...looks very borderline for any potential headlines for this
particular time period. In another similarity...the lingering
associated upper level trough retains sufficient moisture to allow
for the prospect of showers to continue into Wednesday.  SMR

.LONG TERM...Even the weather is taking part in cyber week sales
apparently...as W WA will get two ridges for the price of one. An
upper level ridge looks to move over the area late Wednesday
night/early Thursday morning and keep conditions dry for Thursday
and into Friday morning. GFS run from 24 hours ago indicated that
even the first half of Friday may prove dry...but looks like that
limited time offer has expired as current GFS run is leaning toward
ECMWF solution of bringing system for Friday south enough to bring a
quicker return to precip over the area. Generally zonal upper level
flow will keep moisture moving over the area and a shortwave
disturbance looks to set up right along the Cascades and as
such...would appear that a damp weekend is in the cards.  SMR

&&

.AVIATION...North northwesterly flow aloft into Tuesday
morning. At the surface onshore flow will weaken late tonight.

Clouds have mostly scattered out in the wake of Sunday evenings
front. Convergence near KPAE keeping ceilings in the 3000-4000 foot
range. Even with the strong low level onshore flow drying
northwesterly flow will keep mostly just scattered cloud cover over
the area this morning into the afternoon hours. As the flow aloft
weakens and the low level flow becomes light expect a combination of
low stratus and fog to form late Monday night into early Tuesday
morning. Best chances for lifr fog over the Southwest Interior.

KSEA...Scattered clouds into the afternoon hours. Ceilings
developing late tonight around 1000 feet. Southerly wind 84 to 8
knots. Felton

&&

.MARINE...Gales have come to an end over the waters early this
morning. Low level onshore flow continuing with small craft advisory
winds over all waters except the Puget sound and Hood Canal today.
Winds easing all areas tonight as surface high pressure builds over
the area. The surface high will remain over the waters Tuesday. The
front will arrive Tuesday night with gales possible along the coast
and entrances to the Strait of Juan De Fuca.

Westerly swells will build into the 16 to 19 foot range along the
coast and at the West Entrance to the Strait today. The near 20 foot
swells will continue tonight before subsiding on Tuesday back down
to 11 feet. Felton

&&

.HYDROLOGY...From previous discussion...The Chehalis at Porter
crested this morning and it is a little below flood stage this
evening. The flood warning will continue tonight though, because it
takes about 12 hours for the water to move downstream from Porter to
the mouth of the river. And the high tide late this evening at
Aberdeen will briefly worsen the flooding on the Chehalis surge
plain.

Landslides remain a concern. USGS landslide indices show a continued
threat from the recent heavy rain. A minor landslide was reported
near Quilcene on Saturday. A special weather statement still in
effect addresses this.

After the current flooding has ended, more flooding is unlikley
over the next seven days. McDonnal

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory until 7 AM PST Monday for Cascades of
     Pierce and Lewis Counties-Cascades of Snohomish and King
     Counties-Cascades of Whatcom and Skagit Counties-Olympics.

PZ...Small craft advisory all waters except Puget Sound and
     Hood Canal.
     Small craft advisory for rough Grays Harbor bar.

&&

$$

www.weather.gov/seattle

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



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