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afdsew 


Area forecast discussion 
National Weather Service Seattle Washington 
900 PM PDT Friday Jul 4 2008 


Synopsis...isolated showers will linger this evening...then the 
tail end of another system will bring a little rain to the area on 
Saturday. Look for dry weather with near or slightly above normal 
daytime temperatures on Sunday under weak high pressure aloft. A 
warming trend will keep skies mainly sunny next week. 


&& 


Short term...radar indicates just a few isolated showers around 
western Washington. Most the weak cells are occuring along the 
Strait and over the SW interior near Olympia and Tacoma tracking 
northeastward but weakening as they do so (pic0). As the upper level short 
wave overhead moves east (pic1) and also the loss of daytime 
heating...showers should diminish rather quickly after Sundown. Most 
areas will remain dry for the fireworks and any renegade shower that 
does pop up will only produce some very brief precipitation. A dry period 
is expected during the overnight hours ahead of the next system. 


Models bring rain to the coast by 12z Saturday morning 
(pic2)...spreading inland through the morning. Some shadowing is 
indicated by both the NAM/GFS (pic3) from around Tacoma north to 
Everett where less rain is expected. However...is will be a rather 
cloudy and cool day with most the area stuck in the 60s. Likely probability of precipitation 
along the coast and north interior with chance probability of precipitation elsewhere look good. 


Heights rebound Saturday night with showers decreasing. There will 
probably be some lingering clouds Sunday morning with onshore 
gradients and residual moisture....but northwest gradient in the afternoon 
bodes well for some clearing (pic4). 500mb heights build to around 
5770m in the afternoon so temperatures should Jump Up into the middle 70s even 
with the onshore flow. Onshore gradients weaken on Monday with 
heights above 5800m (pic5). Current forecast temperatures may be a tad on 
the cool side with low 80s a good bet across much of the Puget Sound sound 
region under mostly sunny skies. 


Mercer 


Long term...previous discussion follows...with onshore flow have 
indicated a broad brush typical diurnally varying Summer 
pattern...with areas of late night and morning clouds...and mostly 
sunny in the afternoon. Again have forecast temperatures at the high end of 
the ensembles. Heights remain in the 580s and there should be no 
problem getting well into the 70s each day. Models indicate a weak 
trough on Friday depressing heights and have gone slightly cooler 
then. Burke 


&& 


Aviation...a weak cold front in the offshore waters is pushing 
gradually eastward and will move into the interior of western 
Washington Sat afternoon (pic10). Stratus with bases around 010-015 
are occurring in advance of the front along the coast (pic11). A 
higher based deck around 035-050 will spread inland this 
evening...then lower to around 015-020 Sat morning in advance of the 
front. There will be some holes in the clouds to the Lee of the 
Olympics as a 20-25 knots SW wind 030-060 interacts with the terrain 
(pic12). Light precipitation will accompany the front Sat 
afternoon...but 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 18z 
then through the interior about 00z (pic12). 


Ksea...expect status quo through about 11z with sct035 bkn050-070. 
Expect bkn015-020 to develop 12z-14z time frame and persist through 
about 20z before lifting somewhat with slightly increased flow and 
destabilization of the air mass with diurnal heating Sat. -Shra will 
affect the terminal or approaches at times Sat with periods of 
clearing 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 Sat in advance of the front as the air mass destabilizes and 
mesoscale scale lower pressure develops to the NE of the Olympics. Albrecht 


&& 


Marine...a weak cold front well offshore (pic10) will move through 
the coastal waters Sat morning and through the inland waters late 
Sat afternoon (pic12). Expect Small Craft Advisory S winds in 
advance of the front tonight and Sat morning along the coast...and 
Sat afternoon in the northern inland waters southward to the East Entrance 
to the Strait. Once the front passes wind will turn SW-west and 
decrease...except in the central and eastern Strait of Juan Delaware fuca 
where Small Craft Advisory westerly conditions are expected in onshore flow. 


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 sun-Tue. 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 through early next week. 
Albrecht 
put it up. GFS/NAM agree on a Saturday morning frontal passage on the coast 
&& 


Sew watches/warnings/advisories... 
pz...Small Craft Advisory coastal waters. 


$$ 


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