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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Thursday
• 
• High: 61 °
• Low: 52 °
• Rain Showers

• Friday
• 
• High: 61 °
• Low: 52 °
• Chance of Rain

• Saturday
• 
• High: 64 °
• Low: 52 °
• Chance of Rain

• Sunday
• 
• High: 63 °
• Low: 54 °
• Chance of Rain

• Monday
• 
• High: 63 °
• Low: 54 °
• Mostly Cloudy

Area forecast discussion 
National Weather Service Seattle Washington 
320 am PDT Thursday Jun 20 2013 


Synopsis...an upper level low is over the Pacific northwest. Rain 
will increase across the area today...heavy at times in the north 
Cascades. Weak high pressure will build into the area Friday night 
and Saturday giving drier weather. Rain is likely early next week as 
weather systems move through the region. 


&& 


Short term...a broad and somewhat disorganized upper low will be 
over the Pacific northwest today. Moisture wrapping around the 
north side of the upper low will bring rain to western Washington 
today...starting with the northern areas...and sagging south over 
most of the area duringh te day. There will also be decent 
orographic west/northwest winds aloft enhancing rainfall amounts 
over the north Cascades. Much of the north Cascades should see one 
to two inches of rain today with locally higher amounts possible. 
Rainfall amounts will taper rapidly from north to south with areas 
south of Seattle only seeing a few hundredths. There will also be 
some breezy southerly winds today...especially over the north 
interior...in response to falling pressures over British Columbia. 
Highs today will be several degrees below normal with rain at times 
and lots of cloud cover. 


Showers will taper tonight and mostly end by Friday evening as the 
upper low pulls away from the region and weak high pressure aloft 
builds over the area. It still looks pretty cloudy Friday with 
residual moisture lingering but it will be drier and a couple 
degrees warmer. There might even be some afternoon sunbreaks. High 
pressure aloft will be in control Saturday with high temperatures 
warming back into the 70s and plenty of sunshine. Schneider 


&& 


Long term...a weakening negatively tilted upper trough will 
approach the area from the west on Sunday. Models are still 
struggling with the details. The European model (ecmwf) and Gem take the system 
onshore to the south leaving western Washington mainly dry. The GFS 
pushes the trough inland over the area with a little light rain. A 
second system had been advertised for Monday but models are now 
pushing most of this system onshore to the south as well. For 
Tuesday and Wednesday a large upper trough will dominate the eastern 
Pacific with moist southwest flow aloft for western Washington. 
There will probably be another weather system moving onshore with a 
little rain during this period but the details are hopelessly 
muddled for now. Schneider 


&& 


Aviation...broad upper level low over the area today moving slowly 
east. Light flow aloft becoming easterly this afternoon. Air mass 
moist and stable with low level onshore flow. 


Doppler radar shows light rain rotating back around the low as far 
south as Snohomish County at 10z. The rain will slowly sag south 
reaching Olympia by midday. Ceilings in the 4000 to 6000 foot range 
lowering down near 2000 feet during the morning hours with the lower 
conditions continuing into the afternoon. The exception to this will 
be the central coast where the rain will not arrive until late 
afternoon. In addition to the lowering ceilings reduced 
visibilities...3-5 sm...possible with the rain over the northern 
portion of the area this afternoon. 


Ksea...ceilings at or above 5000 feet early this morning. Increasing low 
level onshore flow with ceilings lowering down to near 2000 feet 
14z-17z. Ceilings remaining near 2000 feet into the afternoon hours 
with light rain. Southerly winds 8 to 12 knots. Felton 


&& 


Marine...low level onshore flow across the waters today with a 
surface low over the interior of British Columbia and high pressure 
building over the coastal waters. Gale warnings are up for the 
central and eastern Strait of Juan Delaware fuca this morning and northern 
inland waters for later this morning into the afternoon. Winds will 
ease tonight as surface high pressure builds onshore. High pressure 
over the waters on Friday into Saturday. A front will approach the 
coastal waters on Saturday and move inland on Sunday. A splitting 
system will follow on Monday. Felton 


&& 


Sew watches/warnings/advisories... 
Washington...none. 
Pz...Gale Warning central and eastern Strait this morning. 
.Gale Warning northern inland waters after 8 am. 
.Small Craft Advisory northern inland waters until 8 am. 


&& 


$$ 


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