Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 161635
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
935 AM PDT Wed Aug 16 2017

.SYNOPSIS...An upper level ridge moving over the Pacific Northwest
coupled with low level onshore flow will maintain seasonable summer
weather with areas of morning clouds into Friday. A weak upper level
trough is expected to bring some cooling and possibly some drizzle
Friday night into Saturday. Another upper level ridge will rebuild
over the region Sunday through Tuesday.

&&

.SHORT TERM...The westerly flow aloft with embedded weak
shortwaves across the Gulf of Alaska continues this morning. The
first shortwave was moving into British Columbia this morning.
Doppler weather radar showed a few showers mainly aloft moving
across southern Vancouver Island to the north side of the Olympic
Peninsula.

Marine stratus was hugging the coast with some pushing into eastern
Grays Harbor County. The KUIL raob shows tops near 2600 ft.
Otherwise generally clear skies in the interior though will see some
increase in higher clouds with the remains of the BC shortwave later
today. Have nudged high temperatures up a bit in the interior.

Low level onshore flow should increase later today and tonight. That
change should draw marine clouds into much of the interior overnight
and Thursday morning. But upper level ridging gets underway as well
with rising heights. So expect the marine clouds to give way to
sunshine as the current forecast notes.

By Friday, the upper ridge axis leans inland with heights beginning
to fall as the next shortwave approaches. Updated the forecast
package to reflect a few adjustments for today. Buehner

.LONG TERM...From the previous discussion...
Upper level troughiness looks to linger over the area for the
weekend but again any precip chances look to remain to the north of
the CWA. In fact...impact looks to be fairly minimal as temperatures
may cool a degree or two...but are generally expected to remain in
the mid 70s for the interior lowlands. With all eyes on Monday...and
hopefully not directly into the sun...models remain consistent
regarding bringing another upper level ridge over the area. ECMWF
and GFS are still a little fuzzy on the details...such as the
amplitude of said ridge...but current solutions continue to show
that clouds generally will not be much of a problem come
showtime...although locations along the coast may have to contend
with some lingering morning stratus. Beyond that...the trough looks
to move east of the Cascades Tuesday potentially setting up for an
upper level low over the Pacific to start influencing local weather
for the second half of the week. Should this solution hold...next
Thu and Fri might look good for some precip.  SMR

&&

.AVIATION...A weak upper level short wave trough will move across
the region today. The main impact from this system will be stronger
low level onshore flow and a deeper marine layer. The flow aloft
will remain from the NW. Wdsprd MVFR CIGs (with areas of IFR
CIGs/MVFR vsbys) over mainly the coast this morning will lift during
the day today. Expect areas of MVFR CIGS over the after 2000 utc.

KSEA...Winds will generally be SW 5-10 kt thru this afternoon before
becoming northerly this evening. Winds will back to light southerly
early Thursday. Expect MVFR CIGs after 0800 UTC (1 AM, Thursday);
otherwise, VFR conditions will prevail.

&&

.MARINE...
Onshore or westerly flow of varying strength will continue through
this weekend due to persistent high pressure offshore with lower
pressure east of the Cascades. Onshore flow strong enough to post a
gale warning in the Strait for later today.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Gale Warning from 3 PM this afternoon to 2 AM PDT Thursday for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

&&

$$

www.weather.gov/seattle/

An illustrated version of this forecast discussion can be seen at
www.wrh.noaa.gov/sew/gafd/latest_webafd.html



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