Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 272203
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
300 PM PDT Tue Jun 27 2017

.SYNOPSIS...Onshore flow will persist into the weekend with a very
typical pattern of late night and morning clouds. An upper level
ridge building over the northeast Pacific on Wednesday will shift
onshore Thursday and Friday with rising heights helping to produce
less morning cloud cover and warmer high temperatures. Another weak
trough will brush the area late in the weekend. &&

.SHORT TERM...The marine stratus has retreated to the coastal
waters this afternoon leaving clear skies over the area except for
the odd mid and high level. The ongoing onshore flow will bring
morning clouds again to the interior again late tonight into
Wednesday morning with afternoon sunshine as the stratus burns back
to the coast again. A subtle change in pattern will occur Wednesday
as the upper level trough over the Pacific Northwest shifts into
Alberta and the northern Rockies.  This will se the stage for
heights to begin to rise as an upper level ridge builds behind it.
Afternoon highs Wednesday will reach into the lower to mid 60s on
the Coast and 60s to mid 70s inland. Lows will mostly be in the 50s.

The building ridge and weaker onshore flow Thursday will help thin
the marine layer, resulting in less morning cloud cover and an
earlier burn off. The earlier clearing and warmer temperatures aloft
will combine to boost high temperatures on Thursday by around 5
degrees with the warmer locations pushing 80 degrees.

.LONG TERM...Medium range models remain in good agreement
through Friday, pushing the ridge axis onshore Friday morning and
over Eastern Washington during the afternoon. Low level onshore will
continue, but with the ridge axis overhead and warming aloft have
boosted the high temperatures a bit over Thursday into mid 70s to
low 80s over the interior and near 70 for the Coast Models have come
into more agreement on the large scale pattern for especially
Saturday. There remains a chance for showers along the Coast early
Sunday morning, but have dried the forecast out for the remainder of
the area on Sunday. Onshore flow expected to increase Saturday night
into Sunday morning resulting in a deeper marine layer in the
morning and a bit less sunshine in the afternoon. Highs will be near
normal, in the 60s and lower 70s. The forecast remains dry Monday
into Independence Day.

&&

.AVIATION...Weak upper level trof over the region will cont moving
slowly E, with upper level ridge following in its wake. Contd NW
flow aloft. The low level flow will remain onshore.

Meanwhile, areas of MVFR CIGs (025-030) persisted over the SW part
of the Puget Sound region and along the SE slopes of the Olympic
range early this afternoon. These clouds will dissipate or lift into
the VFR category range by 0000 UTC, Wed. Expect stratus (MVFR CIGs)
to return to the coast late this afternoon or early this evening and
over the interior lowlands later tonight.

KSEA...Stratus (CIGs near 1k FT) is anticipated to arrive between
1000 UTC (3 AM PDT) and 1200 UTC (5 AM PDT). Expect the low clouds
to scatter out by noon Wed. Winds will be SW 5-10 knots, becoming
light NW late this afternoon or early evening. Winds will become
light southerly overnight.

&&

.MARINE...
Higher pres offshore with lower pres E of the Cascades will maintain
onshore flow of varying strength through this weekend. The flow will
become strong enough on Friday for the possibility of gale force
winds over parts of the Strait of Juan de Fuca.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisories are in effect for the outer coastal
waters from 10 NM out to 60 NM and the central/eastern 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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