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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Thursday
• 
• High: 60 °
• Low: 43 °
• T-Storms

• Friday
• 
• High: 61 °
• Low: 46 °
• Chance of Rain

• Saturday
• 
• High: 59 °
• Low: 45 °
• Chance of Rain

• Sunday
• 
• High: 61 °
• Low: 46 °
• Partly Cloudy

• Monday
• 
• High: 63 °
• Low: 48 °
• Chance of Rain

Area forecast discussion 
National Weather Service Seattle Washington 
315 PM PDT Thursday may 23 2013 


Synopsis...a slow moving cold upper-level low will continue to 
produce showers with isolated evening thunderstorms mainly over the 
mountains. The upper low will wobble around the Pacific northwest 
into the Memorial Day weekend as it slowly fills and weakens. The 
cool air mass will gradually moderate into the weekend and showers 
will gradually diminish starting tonight. 


&& 


Short term...there appear to be two distinct weather regimes over 
western Washington this afternoon. One is scattered showers over 
about the northern third of the area. There are sun breaks and highs 
here will be 55-60. The other is a large area of thick clouds and 
steady rain over the southern two thirds. This is associated with 
the upper level low that is centered along the central Washington 
coast. Under this system conditions are quite gloomy with rain and 
temperatures in the 40s and low 50s. Both kolm and khqm are likely 
to set new low maximum records today. 


The upper low is forecast to move southeast tonight then fill and 
move northeast Friday. At least that is what the NAM and GFS show. 
The Euro keeps the upper low over the area through Sunday. Anyway 
kept chance probability of precipitation in all periods through Sunday...and still have a 
slow warming trend in the forecast. Highs should reach the low to 
middle 60s on Friday and Saturday. By Sunday if the upper low is gone 
and there is zonal flow...a big if...skies should be partly sunny 
and there could be some low 70s around. Burke 


Long term...the GFS continues to bring a weak system inland around 
Monday or Tuesday. The Euro is starting to come around to this idea 
except that it sends the system south into Oregon and California. 
Have rain likely for a few periods in the extended but am not 
confident in the details. Back to scattered showers starting about 
Wednesday. Temperatures are likely to be near normal. Burke 


&& 


Aviation...a deep upper low centered over western Washington this 
afternoon will remain over the region through Friday...probably 
shifting slowly eastward. Flow at the surface and aloft will be 
generally light and variable. The air mass will be moist and weakly 
unstable. 


Fairly solid showery precipitation covers the southern half of the 
forecast area this afternoon...with more scattered showers to the 
north. It will continue through tonight especially over the southern 
two-thirds of the forecast area...and showers should decrease 
somewhat Friday. There is roughly a 15 percent chance of 
thunderstorms this afternoon and evening. 


There was again a wide mix of conditions across the forecast area at 
2 PM. Most of the area had low-end VFR conditions but there were 
also local ceilings of bkn020-030...and much of the coast and south 
interior is IFR where precipitation is more solid. This kind of 
variability will be the rule through tonight and Friday morning. By 
Friday afternoon VFR conditions should become more widespread. 
Confidence in forecast details remains rather low. 


Ksea...mainly southwest wind 4-10 knots...except probably light 
northeast for several hours late tonight. Roughly a 10 percent 
chance of a thunderstorm through this evening. Mcdonnal 


&& 


Marine...a 1014 mb low over the Washington offshore waters will 
weaken and move southeast into northwest Oregon tonight. Weak 
onshore flow will develop Friday and continue Saturday and Sunday. 
Small Craft Advisory westerlies are likely in the central Strait of 
Juan Delaware fuca and East Entrance Friday night...and possibly again 
Saturday and Sunday nights. 


A front will approach the Pacific northwest from the west Monday and 
weaken as it moves inland Monday night. At this point it looks like 
it will produce Small Craft Advisory winds over the coastal waters. 
Weak onshore flow will develop again Tuesday. Mcdonnal 


&& 


Sew watches/warnings/advisories... 
Washington...none. 
Pz...none. 


&& 


$$ 


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