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fxus66 ksew 050936 
afdsew 


Area forecast discussion 
National Weather Service Seattle Washington 
300 am PDT Sat Jul 5 2008 


Synopsis...a weak front will bring periods of rain to the coast 
today and a chance of rain to the western Washington interior. 
Onshore flow will give a cloudy start to the day Sunday...giving way 
to partly sunny skies in the afternoon. An upper ridge will build 
offshore early next week for mostly sunny and warmer days. A weak 
upper trough will approach the forecast area late in the week. 


&& 


Short term...a weak cold front is over the offshore waters moving 
toward western Washington -- it passed buoy 5 around 11 PM Friday. 
This front is the latest...and final...feature associated with the 
deep upper low currently located near 51n/137w. Periods of light 
rain will continue along the coast...with the front making landfall 
midday. The front will reach the Puget Sound sound area late afternoon and 
move through the Cascades by early evening...but it will weaken and 
probably become poorly defined as it moves inland. I will stay with 
chance of rain for the interior lowlands and likely probability of precipitation for the 
Cascades. 


An upper trough will follow the front Saturday evening...keeping a 
chance of showers in the forecast. Low level onshore flow overnight 
will keep western Washington generally cloudy through Sunday morning 
..but the interior lowlands should see some clearing Sunday 
afternoon. Westerly flow aloft will keep a chance of showers in the 
Cascades Saturday night and Sunday. 


An upper ridge will start building weakly along 130w Sunday night... 
and upper level heights over the forecast area will gradually 
recover. The 500 mb height will climb to around 584 dam Monday 
afternoon. Low level onshore flow will continue but weaken during 
this period...so Monday should start with areas of morning low 
clouds in the marine layer but wind up being a mostly sunny day. The 
onshore flow will keep temperatures from warming up too dramatically 
-- highs over the western Washington interior will range from the 
middle 70s to the lower 80s. Mcdonnal 


Long term...the trend established Monday will continue Tuesday as 
the upper ridge continues to build offshore...with upper heights 
climbing over western Washington and onshore flow weakening. A few 
spots in the southwest interior should climb into the middle 80s on 
Tuesday. The ridge will move inland Tuesday night...with a return of 
somewhat stronger onshore flow on Wednesday. An upper trough will 
approach the forecast area Thursday and Friday. Mcdonnal 


&& 


Aviation...a weak cold front currently moving through the offshore 
waters will move onto the Washington coast early this afternoon and 
through the interior lowlands around 00z. Stratus and some light 
precipitation continues to stream onto the coast ahead of the 
front...but has not yet begun to spread inland. Expect low level 
moisture...stratus with bases around 020...to spread into the 
interior around 13-14z. Expect significant breaks in a stratocumulus 
deck to develop in the interior after about 19z as a 20-25 knots SW 
wind at 030-060 interacts with the terrain. Light shower activity 
along the coast ahead of the front will spread inland later this 
morning and this afternoon...but again areas to the Lee of the 
Olympics and terrain of Vancouver Island will see significant holes 
and very light if any precipitation. Timing of the front is to the 
coastline around 20z then through the interior about 00z. 


Ksea...expect status quo through about 13z. A stratus deck 
broken-ovc015-020 will develop by 14z and persist through about 19z 
before lifting and breaking into a higher stratocumulus/cumulus deck 
as SW flow aloft interacts with the Olympics and the boundary layer 
destabilizes somewhat in strong July insolation. -Shra will affect 
the terminal or approaches at times today with periods of clearing 
especially to the north of the terminal as flow aloft interacts with 
the Olympics. Wind S-SW 10-12 knots. Some gusts to 20 knots expected 
18z-24z in advance of the front as the air mass destabilizes and 
momentum mixes downward. Albrecht 


&& 


Marine...a weak cold front moving through the offshore waters will 
reach the coast midday and will move through the inland waters this 
afternoon. Expect Small Craft Advisory S winds in advance of the 
front today along the coast...and at the East Entrance and in the 
inland waters later this morning and afternoon. Flow will become 
onshore behind the front and Small Craft Advisory west winds will 
develop in the central and eastern Strait. The onshore flow will 
decrease after midnight tonight. 


As a ridge of high pressure builds over the offshore waters early next 
week...expect northwest wind to increase 15 to 25 knots in the coastal waters 
by later Mon-Wed. Expect Small Craft Advisory westerly winds to develop each afternoon and 
continue through the overnight hours in the central and East 
Entrance to the Strait of Juan Delaware fuca. Albrecht 


&& 


Sew watches/warnings/advisories... 
pz...Small Craft Advisory coastal waters...East Entrance to the 
Strait...and northern inland waters. 


$$ 


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