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Area forecast discussion...correction 
National Weather Service Seattle Washington 
330 am PDT Sat Aug 30 2008 


Synopsis...cooler weather and isolated showers will continue across 
western Washington through Sunday as an upper level trough passes 
trough the area. A weak cold front will approach the region on 
Tuesday with light rain possible. Dry and warmer weather is expected 
Wednesday through Friday as a strong upper level ridge builds over 
the Pacific northwest. 


&& 


Short term...weak convergence zone still producing light precipitation 
across the central sound this morning although rain amounts have 
been very light...only a trace or a hundredth at best. Showers from 
this weak band will diminish this morning. 


Upper level trough over British Columbia will dig offshore this morning then move 
inland late this afternoon and evening. Overall not too impressed 
with this system as there is not a whole lot of moisture to work 
with. Water vapor imagery is showing all the middle/upper level 
moisture across northern British Columbia and Alberta. And model time height 
cross sections and soundings show a dry airmass above 700 mb. 
Result will likely just be flat cumulus floating around the area. 
Cannot rule out some lift with the upper level trough...but do not 
think we will reach convective temperatures. So did cut back on probability of precipitation today 
and tonight with showers mainly affecting the mountains. Weak cells 
may drift off the Olympics and into Puget Sound sound/SW interior so did 
leave low end chance probability of precipitation in these areas. Upper trough axis will 
shift right over the Cascades by 06z with temperatures at 850mb only 1-2 
degrees c. This will make for another chilly night for campers or 
hikers in the mountains as the snow level lowers to 4000-5000ft. 
Will refresh to Special Weather Statement which highlights cooler 
conditions. 


The upper level trough will dig farther south into southern Oregon and 
California on Sunday with decreasing showers expected across West 
Washington...only left low chance probability of precipitation for the mountains with northwesterly upslope 
flow. Labor Day is still looking dry as weak ridge develops across 
the Pacific northwest. Temperatures on Monday should rebound back into the middle 60s to 
lower 70s which will put US a few degrees below normal. 33 


Long term...a cold front will approach West Washington on Tuesday although new 
GFS and Euro model runs show this system weakening as it reaches the 
coast. In fact...precipitation amounts look rather meager since we will 
still have some ridging over the area. This front may just dissipate 
as it passes through producing nothing more than an increase in 
clouds. As a result...cut back on the probability of precipitation across the area but was 
not completely comfortable with removing precipitation wording just yet. 


Warming/drying trend is still in the forecast for all the 
washingtonians still looking for a few more days of Summer. Broad 
upper level ridge will shift east and into the area by Wednesday with dry 
weather expected through the end of the week. Nudged up temperatures a bit 
and should see 70s to near 80s by Friday if this pattern holds up. 33 


&& 


Aviation...convergence behind a cold front that went through the 
area on Friday giving the central sound a variety of ceilings this 
morning. For the most part ceilings in the 3500 to 6000 foot range 
with lower ceilings...near 1500 feet over the Kitsap peninsula 
extending south through kolm and kcls. Better conditions between 
kbli and kclm with just a scattered-broken layer around 6000 feet while along 
the coast SC deck spreading south with ceilings near 2500 feet. 
WSR-88D VAD wind profile shows northwest winds 20 to 30 knots from 1000 
feet to 6000 feet. With this flow aloft do not expect the ceilings 
to get much lower than they are right now. Some improvement in the 
ceilings later this morning into this afternoon as a cool for August 
upper level trough settles over the area. With the unstable air mass 
associated with the trough a few showers over the area but scattered 
enough to leave out of the terminals. 


Ksea...ceilings near 5000 feet through the morning hours. SC deck 
becoming scattered-broken midday. Winds northerly 4 to 8 knots through the 
afternoon hours. Felton 


&& 


Marine...with a deep upper trough moving across the area...the 
onshore flow will continue through the weekend with Small Craft 
Advisory winds in the central and eastern Strait during the late 
afternoon and evening hours today and Sunday. 


A weak front is expected to dissipate over the coastal waters 
Tuesday. Felton 


&& 


Sew watches/warnings/advisories... 
Washington...none. 
Pz...Small Craft Advisory coast and central and eastern Strait. 
Small Craft Advisory in effect for rough Grays 
Harbor bar conditions. 


$$ 


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