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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Wednesday
• 
• High: 61 °
• Low: 57 °
• Rain Showers

• Thursday
• 
• High: 63 °
• Low: 52 °
• Rain Showers

• Friday
• 
• High: 61 °
• Low: 54 °
• Chance of Rain

• Saturday
• 
• High: 68 °
• Low: 55 °
• Partly Cloudy

• Sunday
• 
• High: 64 °
• Low: 54 °
• Chance of Rain

Area forecast discussion...corrected 
National Weather Service Seattle Washington 
400 am PDT Wednesday Jun 19 2013 


Synopsis...an upper low will produce scattered showers. A trough 
rotating westward to the north of the low will bring a period of 
steadier and heavier rain to much of the area Thursday and Thursday 
night. Weak high pressure will build into the area Friday night and 
Saturday. A series of fronts will bring wet weather again early next 
week. 


&& 


Short term...an upper low just off the coast will slowly shift 
inland over Oregon today. Moist and unstable southerly flow aloft 
will weaken and become more easterly today. There will be isolated 
to scattered showers again today...mostly diurnally driven in the 
afternoon over the Cascades and south part of the forecast area 
closest to the upper low. The thunderstorm threat looks minimal at 
best today with lifted indices this afternoon only down to around 
zero and cape values barely cracking 100 j/kg. There might be an 
isolated storm or two over the south interior or over the Cascades 
later today but the chances are not high enough to mention in the 
forecast. Highs will cool a few degrees today as the upper low moves 
closer. However...guidance has had a noticeable cool bias the last 
few days. The forecast highs for today have been bumped up to 
account for this. 


The upper low will shift over eastern Washington on Thursday. A 
rather well defined short wave rotating around the top of the upper 
low will spread steadier rain into western Washington early 
Thursday. The northern half of the forecast area will see the brunt 
of the rain with amounts rapidly dropping off to the south. The 
heaviest rains are expected to be over the northern Cascades where 
1-2 inches are a good bet by late Thursday with locally higher 
amounts possible. With all the clouds and rain...highs will struggle 
to climb out of the lower 60s...especially from Seattle north. Also 
of note...onshore gradients will tighten in response to falling 
pressures over southern British Columbia as the short wave rotates 
through. This will give breezy southerly winds to parts of the area 
Thursday...somewhat unusual for late June. 


Scattered showers will be tapering on Friday as the upper low 
weakens and pulls away from the area. Even though showers will be 
decreasing...there will be a lot of residual moisture on Friday 
which means there probably will not be much sunshine. As a result... 
highs will only warm a few degrees and be slightly below normal. 
Schneider 


&& 


Long term...Saturday looks and will likely be the warmest day of 
the week with highs in the 70s many areas as a short wave upper 
ridge moves overhead. A frontal system will be approaching from the 
west Saturday night and Sunday. Models are having a hard time 
agreeing on when this system will make landfall and there has been a 
fair amount of run to run waffling as well. If the GFS is correct... 
most of the area will remain dry and highs will be similar to 
Saturday. If the European model (ecmwf) is correct...it will be a rainy and cooler 
day with highs in the 60s. Another relatively wet front will move 
onshore around Monday night. Confidence in the timing and other 
specifics with this front is low for now. Schneider 


&& 


Aviation...upper level low off the South Washington coast moving 
into northwestern Oregon and southwestern Washington today. South 
southeasterly flow aloft becoming more southeasterly late morning. 
Air mass becoming more unstable after 18z with mostly middle level 
moisture. 


Doppler radar shows just a few showers around Stevens Pass at 10z. 
Mostly middle level moisture over the area with a scattered to broken 
deck around 6000 feet and another scattered to broken layer 8000 to 
12000 feet. Little change in the cloud cover throughout the day with 
the shower activity increasing after 21z then decreasing after 
sunset. 


Ksea...middle level clouds throughout the day with the lower layer near 
6000 feet going broken at times. Southerly winds 4 to 8 knots. Felton 


&& 


Marine...high pressure over the offshore waters and low pressure over 
interior b.C. Will maintain onshore flow across western Washington 
through Friday. The onshore gradients will strengthen tonight as 
pressures fall over the interior of British Columbia this afternoon. 
A Gale Warning has been issued for the central and eastern Strait of 
Juan Delaware fuca for tonight. In addition a Small Craft Advisory has 
been issued for the northern inland waters. Winds easing later 
Thursday as surface high pressure begins to build into the area and 
pressures rise over British Columbia. High pressure over the waters 
on Friday. A front will approach the coastal waters on Saturday and 
move inland on Sunday. Felton 


&& 


Sew watches/warnings/advisories... 
Washington...none. 
Pz...Gale Warning central and eastern Strait. 
Small Craft Advisory northern inland waters. 


&& 


$$ 


Www.Weather.Gov/Seattle 


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