Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 282341 AAA
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
300 PM PDT SAT MAY 28 2016

.SYNOPSIS...Showers will continue tonight then taper Sunday as an
upper level low over southern British Columbia moves slowly east. A
strong upper level ridge will build over the area and bring warmer
and drier weather starting Memorial Day and continuing through
the middle of next week.

&&

.SHORT TERM...Showers this afternoon have been behaving as modeled
and are confined mostly to the coast, mountains, and north. Highs
today will be in the upper 50s to mid 60s. Post-frontal tonight and
Sunday morning there will still be scattered showers, more north,
and models show what appears to be a convergence zone. Some
improvement is likely Sunday afternoon and especially Sunday night
as the parent upper trough moves east. Sunday will be a couple of
degrees warmer than today and there will probably be sun breaks over
the inland areas. The coast will probably have some good clearing.

On Monday an upper ridge builds off the coast and heights rise
significantly over Washington. Skies will be mostly sunny and high
temperatures will reach the low 70s. The ridge axis moves over
western Washington on Tuesday. Heights reach the mid 570s and a
thermal trough develops along the coast. This should keep skies
sunny and high temperatures will rise into the low 80s. Burke

.LONG TERM...A similar pattern Wednesday, with both the upper ridge
and the thermal trough moving a bit east, should make that day the
warmest day inland with highs mainly in the 80s. On Thursday and
Friday the surface flow turns onshore, which implies at least some
morning clouds. A recent idea in the GFS is upper level moisture
arriving from the south. Have introduced a chance of thunderstorms
in the Cascades Thursday afternoon and evening.

The GFS brings a weak system onto the coast Friday so have put a
chance of showers there. Models become dry again on Saturday. High
temperatures will fall from around 80 on Thursday into the 70s on
Friday, then rebound somewhat on Saturday. Burke

&&

.AVIATION...
An upper level trough over west-central British Columbia will move
slowly eastward and by to the north of the area tonight through
Sunday. Moist and stable west flow aloft will become more
northwesterly on Sunday. A frontal system moving onshore early
this afternoon will push into the interior valleys by about 5 PM
then move east of the Cascades this evening. High pressure will
build from the northern tip of Vancouver Island southward on
Sunday, giving onshore flow to the region tonight through Sunday
night.

Conditions remain mainly MVFR this afternoon with a pocket of VFR
conditions to the lee of the Olympics in the central Puget Sound
area. IFR conditions remain on the coast early this afternoon.
Conditions are expected to generally become VFR or higher end
MVFR behind mid to late afternoon most areas as the front along
the coast moves eastward, and clearing at times east of the
coastal terrain later this afternoon as the air mass destabilizes
somewhat behind the front and flow aloft interacts with the
terrain. Showers will decrease behind the front and be increasingly
confined to the west slopes of the terrain.

Expect MVFR ceilings to fill back in late tonight through Sunday
morning as low level flow decreases in the cool and moist air
mass. Scattered showers can be expected to continue through Sunday
on the west slopes of the Olympics and in a possible central Puget
Sound convergence zone. Improvement to VFR conditions is expected
midday Sunday with scattered showers continuing on the west slopes
of the mountains and in the convergence zone. Albrecht

KSEA...South to southwest wind 10 to 14 kt with a few gusts to 25
kt through about 01Z. Winds will remain south 5-8 kt this evening
through Sunday morning. Expect cigs to be mostly VFR with showers
remaining away from the terminal. Cigs will fall back to around
BKN025 about 06z then down to around 015 after 11Z. Albrecht

&&

.MARINE...
A frontal system moving onto the coast at 2 PM will push into the
inland waters late this afternoon and east of the Cascades this
evening. Small craft advisory conditions have diminished over the
coastal waters, but continue in all of the inland zones except the
central and western portions of the Strait of Juan De Fuca. Winds
will diminish about 5 pm as the front pushes in and weakens.

Onshore flow and convergence zone activity will likely continue
this evening through late Sunday afternoon or evening behind the
front. Small craft advisory inflow through the Strait of Juan De
Fuca is likely to develop late Sunday afternoon or Evening.

High pressure will increase over the offshore waters on Memorial
Day. This will give the potential for northwesterly winds up to 25
KT over the coastal zones Monday afternoon and evening, and .
winds will become northerly inland. Northerly flow will dominate
on Tuesday as a thermally induced trough of low pressure over
Northern California develops northward into western Oregon. The
trough will push inland as it expands into southern portions of
Washington on Wednesday.

Both the GFS and ECMWF indicate the development of a marine push
Wednesday night as the thermal trough and its associated upper
level ridge of high pressure moves east of the Cascades. Albrecht

&&

.SEW Watches/Warnings/Advisories...
WA...None.
PZ...Small Craft Advisory until 5 PM PDT this afternoon for Admiralty
     Inlet-East Entrance U.S. Waters Strait Of Juan De Fuca-
     Northern Inland Waters Including The San Juan Islands-Puget
     Sound and Hood Canal.

&&

$$

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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