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Area forecast discussion 
National Weather Service Seattle Washington
934 am PST Friday Nov 27 2015

Synopsis...a strong upper high will slowly meander eastward
across southern British Columbia from now through Sunday...with
some slow weakening on beginning on Sunday. This will keep
western Washington clear and dry through the remainder of
Thanksgiving weekend. The upper high will break down at the start
of next week...allowing Pacific frontal systems to bring a return
to more typically wet weather.


Short term...a strong blocking upper high was centered over
northern Vancouver Island this morning...with the 12z port Hardy
sounding registering a 500 mb height of 575 decameters. It will
take all the way through Sunday for this feature to slowly meander
eastward across southern b.C.. in the will continue
to support dry NE/east flow aloft over western Washington...and the warm air
aloft will lead to stable conditions with strong low-level

So that leaves air stagnation as the main issue with which to
contend. Already this morning...both Marysville and South Tacoma
were in the air quality category of unhealthy for sensitive
groups due to wood smoke. Qualitatively...there is a little more
low-hanging Brown haze out the window here in northeast Seattle
this morning than yesterday. Looking ahead...pressure gradients
will be quite weak through Sunday...and the warmest air aloft
appears to come on Saturday night. Will mostly likely take until
Monday for smoke dispersion to improve.

By Monday...both the 12z GFS and 12z NAM models take the weakened
center of our blocking high east into Alberta. This would allow a
shortwave impulse to brush the area on Monday. At the least...this
would improve mixing and air quality by removing the cap of warm
air aloft and bringing a modest increase in wind. At the
could also bring some clouds and a little rain. Regarding
rain...amounts would be light. It is fairly typical for the first
system trying to budge a blocking high to fizzle as it fights its
way into a dry air mass...but it may also help open the door for a
return to typically wet and active weather beyond Monday. Will
have to consider increasing probability of precipitation for Monday in the next forecast

Long term...from previous discussion...the upper high should be
out of the picture for western Washington by Monday...with
southerly flow aloft developing as an upper trough approaches the
Pacific northwest from offshore. Models have been inconsistent
with regard to when the first frontal system will bring
precipitation back to the forecast area...but a weak one will
probably arrive by Tuesday and possibly even on Monday. The cold
air mass over The Lowlands should mix out fairly quickly as all
this occurs. A wetter system should arrive by Wednesday...and wet
weather will likely continue Thursday. Mcdonnal

&& the strong upper level ridge over the Pacific
northwest this morning drifts slowly will maintain cool
dry northeast flow aloft over western Washington through this
weekend. A weak surface ridge over southern British Columbia will
maintain dry north to northeast low level offshore.

The air mass will remain dry and stable through the weekend with
minimal fog or stratus in the morning. Morning air temperatures will
be near or below freezing so isolated freezing fog is possible.

Ksea...clear skies. Surface wind northerly 4-8 knots. Kam


Marine...a strong surface ridge over southern British Columbia will
maintain light northeasterly flow today. The ridge will weaken this
afternoon with light offshore flow continuing over the interior
though the weekend. On an offshore frontal system
approaches the region winds over the coastal waters will shift to
southerly and begin increasing.

East winds at the Neah Bay buoy have dropped to 10-12 knots this morning
and the latest 06z Canadian lam...00z arw...and 15z hrrr keep the
winds below Small Craft Advisory levels the rest of the Small Craft Advisory for the West
Entrance and coastal zone 150 will be ended.

Models have been doing their typical wiggle-waggle in the day 3-5
period and have sped up the timing of the next frontal system back
to sometime on Monday. Winds over the coastal waters will shift to
southerly on Sunday and begin increasing ahead of the approaching
front. Subsequent frontal systems arriving midweek and later will
likely be stronger with potential for gales at some point.

The current period of King tides will have the highest tides this
year. Fortunately strong high pressure over the area and relatively
light winds appear likely to keep the tidal anomalies minimal. No
coastal flooding is forecast during the high tides. Kam


Hydrology...flooding is not expected for the next seven days.


Sew watches/warnings/advisories...
Washington...air stagnation advisory until noon PST Monday for Admiralty
Inlet area-Bellevue and vicinity-Bremerton and vicinity-
east Puget Sound sound lowlands-eastern Strait of Juan Delaware fuca-
Everett and vicinity-Hood Canal area-lower Chehalis valley
area-San Juan County-Seattle and vicinity-southwest
interior-Tacoma area-western Skagit County-western Strait
of Juan Delaware fuca-western Whatcom County.




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