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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Wednesday
• 
• High: 57 °
• Low: 46 °
• Rain Showers

• Thursday
• 
• High: 59 °
• Low: 46 °
• Rain Showers

• Friday
• 
• High: 70 °
• Low: 48 °
• Partly Cloudy

• Saturday
• 
• High: 70 °
• Low: 52 °
• Clear

• Sunday
• 
• High: 64 °
• Low: 50 °
• Chance of Rain

Area forecast discussion 
National Weather Service Seattle Washington 
930 am PDT Wednesday may 23 2012 


Synopsis...cool showery weather will continue today and tonight as 
an upper low approaches the area from the northwest...then decrease 
gradually Thursday as the upper low makes its way southeast. An 
upper ridge will bring mainly dry and warmer weather Friday and 
Saturday. Another upper trough will move through Sunday and Memorial 
Day for a chance of showers. 


&& 


Short term...scattered showers will roll through western Washington today 
as onshore flow continues. An upper level low over west-central b.C. 
Will maintain an unstable air mass over the region. The focus for 
heavier showers will be over the north sound where a pscz is located 
- although it is a bit diffuse on radar. The freezing level is 
around 4000 feet so the higher mountain passes may see a few inches of 
snow. Paradise picked up 6 inches over the last 24 hours. There is 
little change in the pattern tonight so expect a few more showers. 


The upper level level low will cross over western Washington on Thursday for more 
cool and showery weather. Onshore flow will weaken for a decrease in 
activity...but there is also a slight chance of thunderstorms under 
the cold pool. Model Li is under zero for much of the area but the 
best chance of seeing stronger showers will be over the coastal 
waters...coast and mountains. 


Friday will be drier and warmer as the upper level low exits. Temperatures 
should rebound back closer to normal with highs in the middle 60s. 
Northerly flow will help scour out some moisture and we should see 
mostly sunny skies. 33 


Long term...previous discussion...the longer range models are in 
fairly good agreement that a progressive pattern will prevail 
Saturday through early next week...and they show similar timing. On 
Saturday the upper ridge axis will shift slowly southeast across 
British Columbia...while the upper low moves northeast from 
California into the northern Rocky Mountains. Western Washington 
should have another mostly -- or at least partly -- sunny day with 
afternoon and evening showers popping up over the mountains. The 
upper ridge will move across our forecast area Saturday night and 
east of the Cascades Sunday. The next upper trough will move through 
the Pacific northwest Sunday and Monday... and another weak upper 
ridge will arrive on Tuesday. Mcdonnal 


&& 


Aviation...westerly flow aloft over Washington today will weaken 
tonight. Moderate onshore surface flow will continue today then ease 
late tonight. Air mass is moist and slightly unstable. An upper 
level low will move south off the coast on Thursday. 


Ceilings are MVFR 1-2k feet around central Puget Sound sound with the lower 
end near the Puget Sound sound convergence zone. Away from Puget Sound sound 
ceilings are mainly VFR. Should be some improvement to low end VFR 
this afternoon followed by a fall back to mainly MVFR overnight. 


Ksea...discussion above applies. Wind will be southwest 10g20 today 
then ease tonight. Chb 


&& 


Marine...moderate onshore flow will continue to give Small Craft 
Advisory strength winds to the coast and Strait today. The GFS model 
shows a gradient down the Strait strong enough for gale force winds 
this evening but other models do not support that. Have kept winds 
at 15-25 knots in the Strait through this evening. 


Onshore flow will ease Thursday. For now have kept all winds below 
20 knots on Thursday. On Friday the gradients turn northerly and could 
generate some Small Craft Advisory strength northerly winds over the 
inland waters. Flow turns onshore again over the weekend. Chb 


&& 


Sew watches/warnings/advisories... 
Washington...none. 
Pz...Small Craft Advisory coast...central and east Strait. 


&& 


$$ 


You can see an illustrated version of the forecast discussion at 
www.Weather.Gov/Seattle/gafd/latest_webafd.Html