Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 301613
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
913 AM PDT MON MAY 30 2016

.SYNOPSIS...
Upper level ridging will move slowly east across western
Washington today and Tuesday bringing sunny skies and a short
warming trend. A marine push will begin Tuesday night and
strengthen on Wednesday as a weak weather system moves across the
area. The system will bring increasing clouds Wednesday and a
chance of showers on Thursday. Another upper level ridge will
build next weekend for sunny and warmer conditions.

&&

.SHORT TERM...
High pressure at the surface and aloft is building just inside of
130W this morning. The pattern is somewhat progressive, so the
upper ridge will move into western Washington late tonight the
move east of the Cascades Tuesday night and Wednesday.

Thermal troughing is sitting along the far southwestern coast of
Oregon this morning. As high pressure at the surface bridges
northeastward across British Columbia tonight and Tuesday, expect
the thermal trough to expand northward on the Oregon coast late
tonight then shift eastward across far southern Washington Tuesday
afternoon on its trek east of the Cascades Tuesday night. The
models continue the idea of the thermal trough remaining just to
the south of the forecast area, and 500 mb heights top out around
575 dam Tuesday afternoon.

With full sunshine and a dry air mass in place today, expect
temperatures to rise into the 60s near the water and into the
lower to mid 70s away from the water and from about Seattle
southward in the interior. On Tuesday, expect dry and clear
conditions to contribute to highs around the 80 degree mark in
Seattle and into the mid 80s in the south interior with areas near
the water staying in the 70s. With maximum temperatures expected
to be 2-3 degrees warmer than the overnight forecast and
conditions clearer, will issue a minor morning update for the
periods from today through Tuesday.

As thermal troughing shifts east Tuesday night and a frontal
system over the offshore waters approaches the region, expect
marine air to push inland late Tuesday night and onshore flow to
increase on Wednesday. The current temperature forecast for
Wednesday may be a few degrees too high and clouds may not be
sufficient, but will take a look at the full suite of 12z models
and guidance before changing the forecast beyond Tuesday. Albrecht

.LONG TERM...
From the overnight long term discussion: Late Thursday and into
Friday...models agree that ridging will rebuild of W WA...but
there is some discrepancy on the timing. GFS proves to be
progressive as usual...wrapping up any potential for precip by Thu
night...while the ECMWF likes to cling to the moisture into Fri
before allowing the ridge to rebuild into the area. The Canadian
tends to follow the slower ECMWF solution. Have opted to take a
compromise of these solutions...keeping very low end chance pops
in the forecast for Thu night and Fri morning with slight chance
pops in for Fri afternoon and drying things out by Fri night. This
ridge should linger long enough to provide a dry start to the
weekend and a return to warmer temps. SMR

&&

.AVIATION...
An upper level ridge building offshore will shift over
Washington tonight and Tuesday. Northwesterly flow aloft becoming
westerly on Tuesday. The air mass is stable and dry.

Clear skies through Tuesday with a few high clouds passing
through.

KSEA...Clear skies with northerly wind 5-9 kt becoming northeasterly
after 05z. Felton

&&

.MARINE...
Thermally induced low pressure along the Oregon coast will
nudge northward along the southern Washington coast tonight and
Tuesday. This will maintain northerly flow over the waters with the
strongest winds up to 20 kt over the south part of the coastal
waters tonight.

The low pressure trough near the coast will shift inland
Tuesday...and east of the Cascades Tuesday night. Onshore flow is
expected to resume Tuesday night and continue through the week.
Winds are likely to reach Small Craft Advisory criteria in the
central and east portions of the Strait of Juan de Fuca during the
evening and early morning hours Tuesday and Wednesday.

A weak front will reach the coastal waters late Wednesday night and
dissipate over the inland waters Thursday.  DTM/Felton

&&

.SEW Watches/Warnings/Advisories...
WA...None.
PZ...None.
&&

$$

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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