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afdsew 


Area forecast discussion 
National Weather Service Seattle Washington 
300 am PDT sun Jul 20 2008 


Synopsis...weak high pressure will remain over the region today. An 
upper trough will brush Washington on Monday and Tuesday with 
stronger onshore flow. A weak ridge will build Wednesday and 
Thursday with another trough to affect the area Friday into next 
weekend. 


&& 


Short term...latest satellite imagery shows some patchy low clouds 
along the coast...west Strait and SW interior early this morning. A few 
patches of stratus may form over the interior just prior to day 
break...but the majority of US will wake to sunny skies. High 
pressure and light surface gradients will allow any low clouds that 
do form to quickly clear by middle morning...even along the coast. 
Upper heights rebound above 5800m today with light onshore flow this 
afternoon. Stayed close to MOS on temperatures today with 70s to around 80 
expected around the Puget Sound sound region...with the SW interior the 
warmest spot. 


An upper low tracking across British Columbia tonight will brush 
Washington...resulting in lower heights and a increasing onshore 
flow Monday. Marine stratus will develop along the coast and 
probably spread inland as a decaying front drags across the area. 
The front should fizzle out with some scattering in the afternoon 
but cooler overall due to the marine influence. A larger drop in 
temperatures expected Tuesday as stronger southwesterly gradients develop over the 
area. Stratus should become widespread across western Washington and it could 
take most the day to break out. 


Long term...weak high pressure builds Wednesday and Thursday with 
weak onshore flow continuing. Expect dry weather and slightly warmer 
temperatures. Another trough will approach the coast Friday and 
shift over the area through the weekend. This will result in 
stronger onshore flow....more clouds...and cooler temperatures. The 
GFS is spitting out some low quantitative precipitation forecast amounts probably in the form of 
drizzle...but nothing organized enough to add into the extended at 
this point. Mercer 


&& 


Aviation...satellite imagery shows stratus developing along the 
coast...Strait...and between knuw and kfhr. The remainder of the 
area pretty clear. Not much change in aerial coverage of the stratus 
through the middle morning hours with only stratus left along the coast 
by 17z. With the westerlies in the Strait could see the stratus make 
a run at kpae. For now will leave low scattered deck for the first 
few hours in a the taf there. 


Ksea...clear skies with light northerly increasing to 6 to 10 knots 
in the afternoon. Felton 


&& 


Marine...high pressure will remain offshore with lower pressure 
east of the Cascades...producing onshore flow across western 
Washington. The strongest winds will generally occur during the late 
afternoon and evening hours as a result of daytime heating. This 
large-scale pattern will continue through Wednesday. 


Small Craft Advisory westerly winds expected for the central and 
eastern Strait of Juan Delaware fuca each late afternoon and evening 
through Thursday. Low end gale force winds possible Monday evening. 
Felton 


&& 


Sew watches/warnings/advisories... 
.Small Craft Advisory...Central Strait...East Entrance. 


$$