568 
fxus66 ksew 182208 
afdsew 


Area forecast discussion 
National Weather Service Seattle Washington 
300 PM PDT Friday Jul 18 2008 


Synopsis...moderate onshore flow will continue for the next several 
days as weak disturbances ride by to the north of the area in 
westerly flow aloft. Expect minor day-to-day fluctuations of near 
normal daytime temperatures and late night and morning low clouds. 


&& 


Short term...deep marine air with tops near 4500 feet continues 
this afternoon. There has been sufficient daytime heating with the 
strong July sun to thin and break the overcast this afternoon. 
Expect skies in the interior to become partly cloudy over the next 
hour or two as the warming process continues. Clouds will tend to 
redevelop overnight across the area with tops near their current 
values. But cloud bases will rise a few hundred feet Saturday 
morning over this mornings value. 


Short wave ridging now near 130w is damping as it approaches the 
trough from eastern b.C. Southward. The weakening ridge and high 
static stability in the boundary layer will inhibit much effect on 
temperatures at the surface Saturday. Models ... the 18z 
solutions-- are inconsistent from previous runs concerning timing of 
small scale features moving by to the north of the area in west-southwest flow 
aloft. This will affect temperatures and the extent and depth of the 
marine layer Sunday and Monday. At this time will stick with the 
idea that Sunday will be warmer with less marine air...followed by a 
fresher push of marine air Sunday night and Monday. Albrecht 


Long term...the general pattern Tuesday through Friday will be one of west-southwest 
flow aloft...modest 574-580 dam 500 mb heights over the area...and 
moderate onshore flow in the lower levels. Small deviations in the 
strength of individual features lifting by to the north would impact 
the depth of the marine air and daytime temperatures. At this point 
will broad brush the extended forecast. Albrecht 


&& 


Aviation...westerly flow aloft over western Washington will 
continue tonight and Saturday. An upper level low near Jasper 
Alberta move east into Saskatchewan Saturday. At the surface high 
pressure remains over the northeast Pacific Ocean with lower 
pressure east of the Cascades giving low level onshore flow. Air 
mass is stable with low level marine moisture below 4500 feet. 


Marine stratus has been gradually lifting and breaking up since late 
this morning. This process will continue late this afternoon and 
evening...but stratus develop again tonight with widespread overcast 
based 1500-2000 feet with tops around 4500 feet between 09z-18z. Expect 
gradual improvement again late Saturday morning and afternoon. 


Ksea...stratus will return tonight with ceilings roughly 1000-1800 
feet 09z-21z Saturday. Southwest wind 6-12 knots...becoming north 5-10 knots 
this evening...then southerly 4-8 knots around midnight. Mcdonnal 


&& 


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. 


Another round of Small Craft Advisory westerly winds will occur in 
the central Strait of Juan Delaware fuca and East Entrance early this 
evening through tonight...with a repeat performance each day during 
the forecast period. Mcdonnal 


&& 


Sew watches/warnings/advisories... 
Washington...none. 
Pz...Small Craft Advisory central and east Strait of Juan Delaware fuca. 




$$