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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Sunday
• 
• High: 66 °
• Low: 48 °
• Partly Cloudy

• Monday
• 
• High: 72 °
• Low: 52 °
• Partly Cloudy

• Tuesday
• 
• High: 63 °
• Low: 48 °
• Rain

• Wednesday
• 
• High: 61 °
• Low: 50 °
• Mostly Cloudy

• Thursday
• 
• High: 66 °
• Low: 52 °
• Partly Cloudy

Area forecast discussion 
National Weather Service Seattle Washington 
938 am PDT sun may 19 2013 


Synopsis...an upper ridge will build into the region today...then 
cross the area on Monday morning...for warmer and drier weather. A 
large upper low will drop into the area on Tuesday and remain over 
the region through the remainder of the week for showery weather and 
below normal temperatures. 


&& 


Short term...have already update the first period forecast to add 
20-40 probability of precipitation to the Puget Sound sound lowlands due to ongoing light showers 
and sprinkles moving south from Admiralty Inlet. With a northerly 
surface breeze and a subsidence inversion around 8000 feet today...expect 
the lowland showers to dissipate this afternoon. Looking for clearing to 
develop over the inland waters this afternoon...with sunnier skies 
spreading out over land areas this afternoon. With onshore flow and 
shallow instability beneath the subsidence inversion...would expect 
showers or sprinkles to continue through this afternoon over the 
Cascades...foothills...and around the perimeter of the Olympics. 


An upper ridge axis will continue to build into western Washington tonight. The 
ridge axis should move across western Washington during the overnight hours. 
With clear skies tonight...expect cool temperatures. Should be a few cold 
pocket locations...such as kolm...down into the upper 30s tonight. 


On Monday...the ridge axis will be east of the Cascades...and an 
upper trough will dig and amplify out around 135w-140w. With 
offshore low pressure easing the onshore pressure gradient...and 
light southerly flow at 850 mb...Monday should be one of those warm and 
dry day in advance of tuesday's strong cold front. 


Speaking of Tuesday...the offshore upper trough will advance east between 
130w and the coast and then become a cutoff low that sinks southeast off 
the Washington and Oregon coasts. A strong cold front will push onshore and 
inland on Tuesday morning. The front will be accompanied by a band of 
rain...then followed by convective showers on Tuesday afternoon and evening. In 
typical fashion...showers will focus on windward side of mountains and in 
the Puget Sound sound convergence zone. An unseasonably cool air mass will 
follow the front...with 850 mb temperatures down in the -1c to +1c range by 
Tuesday evening. This will lower snow levels as low as 3000 feet at sunrise 
on Wednesday morning. A few inches of snow are expected at the higher 
Highway passes which have already opened for the Summer...including 
Chinook Pass. Haner 


Long term...from previous discussion...as the case has been for 
some time now...the models continue to be at odds with the evolution 
of the trough from Thursday on through the Holiday weekend. There 
are likely to be some dry periods at times...but a series of 
disturbances rotating through the trough will brings showers or 
perhaps a steady light rain. Heights do recover some...so 
temperatures should moderate with time. The 00z run of the GFS takes 
much of the troughs energy and precipitation into the Canadian rockies by 
next weekend...while the 00z Euro keeps the trough centered right 
over Washington state with areas of precipitation spreading into the region 
from the east at times. Details are nearly impossible to put any 
real confidence in for the Holiday weekend...but the trend of cooler 
than normal temperatures and a chance of showers at times looks like 
a good forecast. 27 


&& 


Aviation...the flow aloft will remain northwesterly today with high 
pressure offshore. There were scattered showers popping up in the 
eastern Strait of Juan Delaware fuca area drifting south-southeast across Port 
Townsend and down Admiralty Inlet...but the showers should end later 
this morning with more clearing into the afternoon. Areas of morning 
clouds should lift to mainly scattered cumulus this afternoon...although 
a few areas of broken clouds may persist near the mountains. Skies 
should be mostly clear tonight. 




Ksea...morning clouds then increasing sun in the afternoon. A few of 
the showers coming down Admiralty Inlet may work into the metropolitan area 
this morning. Northerly breeze. 


&& 


Marine...high pressure over the NE Pacific will maintain northwesterly 
flow across western Washington today and Monday. A Small Craft Advisory is in 
effect for the central and east Strait of Juan Delaware fuca through 
tonight and I have added one for the two northernmost outer coastal 
zones since there is a ship report out there with northwest 25kt wind. The 
northwest wind may increase and work toward the coastline later today and I 
would not be surprised to have to put up an advisory for all of the 
coastal waters with the afternoon forecast package. 


A frontal system will track over the offshore waters Monday 
night...then shift south and move inland over Oregon or northern California 
Tuesday morning. Models show a southwest push Tuesday night as this system 
moves farther inland and weakens. The flow will remain onshore 
through at least midweek. 


&& 


Sew watches/warnings/advisories... 
Washington...none. 
Pz...Small Craft Advisory outer coastal waters from Cape Flattery to 
Point Grenville...and the central and east Strait of Juan Delaware fuca. 


&& 


$$