Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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226
FXUS66 KSEW 220428
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
928 PM PDT Wed Jun 21 2017

.SYNOPSIS...An upper ridge will bring dry weather with a warming
trend over the next several days. The ridge will shift inland
early next week with onshore flow developing for a return to more
seasonable temperatures and some night and morning cloudiness.

&&

.SHORT TERM...An upper ridge will gradually build in from the
west over the next few days. At the same time, low level onshore
flow will weaken and turn more northerly. The result will be
sunny weather with a warming trend through Saturday. Highs will be
in the mid 60s to mid 70s Thursday, 70s to lower 80s Friday, and
then in the 80s to near 90 on Saturday. Schneider

.LONG TERM...Previous discussion...The 12Z and 18Z models
continue in good agreement through the middle of next week.

Sunday will likely be the hottest day of this brief warm spell.
Temperatures from about Seattle southward will likely get into the
lower to mid 90s. Highs in the 80s are expected elsewhere as
thermal troughing sets up somewhere between the coast and the
interior. The immediate coast will likely be 2-3 degrees cooler on
Sunday than on Saturday. Anticipated high temperatures will likely
exceed daily records in many locations. A special weather
statement was issued for the anticipated hot weather.

Latest model solutions agree now that a weak push will begin on
Sunday night and will evolve into strong onshore flow later Monday
or Monday night. It will likely be much cooler along the coast on
Monday, and the interior, while still quite warm, will likely see
about 5-8 degrees of cooling.

Temperatures will return to near or slightly below normal
beginning Monday night and continuing into the middle of next week
as marine air floods inland ahead of an upper level trough
offshore. Albrecht

&&

.AVIATION...A flat but fairly strong upper ridge axis will slowly
move from 135W to 130W over the next 24-30 hours, leading to
moderate northwest flow aloft. The air mass will be stable, with
further drying into Friday morning. Clear skies will prevail,
except for some lingering marine stratus near the beaches on Thu
morning.

KSEA...Clear skies for the next 30 hours with prevailing north
wind. Haner

&&

.MARINE...A surface ridge centered about 500 NM offshore will
maintain weak to moderate NW onshore flow through Friday. This
will produce SCA NW winds 15-25 KT over the coastal waters through
Thursday. W flow through the strait will also be in the SCA range
through this evening, but it is already easing earlier in the
evening than the usual diurnal norm. NW wind of 15-25 KT through
the Strait of Georgia will occasionally affect the waters north of
the San Juan Islands through tonight.

The offshore surface ridge will begin building inland over B.C.
on Friday which will shift the low level flow to a N to NE
offshore direction. This dry offshore flow will increase the
warming over W WA, eventually allowing a thermally induced surface
trough over Oregon on Saturday to expand northward along the WA
coast. With onshore flow weakening and becoming offshore, winds
Friday through Sunday should be weak. A shift back to westerly
onshore flow may occur Sunday night or Monday night. Haner/Kam

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Thursday for Coastal Waters
     From Cape Flattery To James Island 10 To 60 Nm-Coastal
     Waters From Cape Flattery To James Island Out 10 Nm-Coastal
     Waters From James Island To Point Grenville 10 To 60 Nm-
     Coastal Waters From James Island To Point Grenville Out 10
     Nm-Coastal Waters From Point Grenville To Cape Shoalwater
     10 To 60 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater Out 10 Nm-Northern Inland Waters Including The
     San Juan Islands.

     Small Craft Advisory for rough bar from 11 PM this evening to 6
     AM PDT Thursday for Grays Harbor Bar.

     Small Craft Advisory until midnight PDT tonight for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca-West Entrance U.S. Waters Strait Of
     Juan De Fuca.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.wrh.noaa.gov/sew/gafd/latest_webafd.html



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