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fxus66 ksew 201736 
afdsew 


Area forecast discussion 
National Weather Service Seattle Washington 
930 am PST Sat Jan 20 2018 


Synopsis...a strong front will move through the area tonight and 
Sunday morning. Another strong front should cross western Washington 
Tuesday night and Wednesday. A cool showery upper trough will reach 
the area Thursday. 


&& 


Short term...a strong front will move into the area tonight. Strong 
southeasterly gradients will develop and a High Wind Warning is in 
effect for the typical windy spots. There will be more snow in the 
mountains and a Winter Storm Watch is in effect. The Skokomish River 
in Mason County should get up above flood stage as heavy rain falls 
in the lower elevations of the Olympics, especially as strong south 
winds aloft push moisture into the terrain in that river basin. 
Precip will taper off Sunday into Monday, though no model is 
completely dry. The air mass will be unstable on Sunday afternoon, 
with showers everywhere and thunder possible on the coast. Monday 
will not be as unstable, but moist onshore flow will still bring 
showers. 


Long term...early Tuesday looks dry. Then a weak front will 
move quickly through the area Tuesday night. Another front will 
arrive around Wednesday, and another one Thursday. An upper trough 
will cool the air mass considerably Thursday night and Friday, with 
showers and low snow levels resulting. Burke 


&& 


Hydrology...the Skokomish River in Mason County has a good 
chance to get above flood stage on Sunday, otherwise river flooding 
is not expected for the next 7 days. I have tried to put a new 
forecast in for the Skokomish River that shows the river rising to 
flood stage of 16.5 feet late Sunday morning, then cresting at 16.8 
feet Sunday afternoon, then falling below flood stage around 
daybreak Monday. For whatever reason the forecast isn't showing up 
on the website as of 930am, but i'll keep trying to get it out. 


Forecast rainfall tonight and early Sunday will push the USGS 
landslide indices close to thresholds for shallow landslides. 


&& 


Aviation...a strong cold front will reach the coast and move 
inland, all on Sunday morning. S-southeast surface wind will become 
strong in advance of the front tonight. Strong 850-700 mb winds 
will peak near 70 knots from the southwest on Sunday morning. The 
air mass will be moist and a little unstable today, becoming more 
stable tonight. A few hours of heavier rain are expected Sunday 
morning, just in advance of the front. Easterly wind component 
will generally hold cigs above 025, except lower near Hood Canal. 


Ksea...will be quite showery at the terminal until about 20z 
(noon), then fewer showers this afternoon and evening. Cigs will 
slowly lift through this evening and low-level wind takes on a 
drying easterly component. Strong winds aloft expected Sunday 
morning. Winds at 045 will peak SW 65 knots, and 2000-foot winds 
will peak southerly around 50 knots. Haner 


Ksea...mainly MVFR conditions with ceilings at fl015-025 today. 
Low level southeasterly flow will help ceilings rise to fl035 
tonight. Wind 19011kt early easing to 16007kt this evening then 
rising to southeast 15 kt after 06z as winds at fl025 rise to S 55 kt. 
Albrecht 


&& 


Marine...east-southeast gradient will tighten significantly 
tonight in advance of a strong cold front that will cross the 
waters on Sunday morning. Storm-force winds to near 50 kt appear 
likely over the coastal waters and at the East Entrance, but 
cannot be ruled out over the northern inland waters. The remaining 
inland waters will likely see gale force winds. In Puget Sound, 
gales should mainly be confined to the north end of the sound. 


Forecast models show an active pattern continuing for much of the 
incoming week with strong fronts or low pressure systems moving 
through the waters Tuesday through Thursday. These systems may 
produce additional rounds of gale force winds. Haner 


&& 


Sew watches/warnings/advisories... 
Washington...Winter Weather Advisory until 10 am PST this morning for 
Cascades of Pierce and Lewis counties-Cascades of Snohomish 
and King counties-Cascades of Whatcom and Skagit counties. 


Winter Storm Watch from this evening through Sunday evening for 
Cascades of Pierce and Lewis counties-Cascades of Snohomish 
and King counties-Cascades of Whatcom and Skagit counties- 
Olympics. 


Wind Advisory from 10 PM this evening to noon PST Sunday for 
Everett and vicinity-Hood Canal area. 


High Wind Warning from 8 PM this evening to noon PST Sunday for 
Admiralty Inlet area-San Juan County-western Skagit County- 
western Whatcom County. 


High Wind Warning from 6 PM this evening to 10 am PST Sunday for 
central coast-north coast. 


Wind Advisory from 10 PM this evening to 10 am PST Sunday for 
eastern Strait of Juan de Fuca. 


Pz...Small Craft Advisory for rough bar until 3 PM PST Sunday for 
Grays Harbor bar. 


Small Craft Advisory until 6 PM PST this evening for coastal 
waters from Cape Flattery to James Island 10 to 60 nm- 
coastal waters from Cape Flattery to James Island out 10 nm- 
coastal waters from James Island to Point Grenville 10 to 
60 nm-coastal waters from James Island to Point Grenville 
out 10 nm-coastal waters from Point Grenville to Cape 
Shoalwater 10 to 60 nm-coastal waters from Point Grenville 
to Cape Shoalwater out 10 nm-West Entrance U.S. Waters 
Strait of Juan de Fuca. 


Storm Warning from 6 PM this evening to 9 am PST Sunday for 
coastal waters from Cape Flattery to James Island 10 to 60 
nm-coastal waters from Cape Flattery to James Island out 10 
nm-coastal waters from James Island to Point Grenville 10 
to 60 nm-coastal waters from James Island to Point 
Grenville out 10 nm-coastal waters from Point Grenville to 
Cape Shoalwater 10 to 60 nm-coastal waters from Point 
Grenville to Cape Shoalwater out 10 nm. 


Storm Warning from 6 PM this evening to 10 am PST Sunday for 
East Entrance U.S. Waters Strait of Juan de Fuca. 


Gale Warning from 6 PM this evening to 10 am PST Sunday for 
Admiralty Inlet-central U.S. Waters Strait of Juan de Fuca- 
northern inland waters including the San Juan Islands. 


Gale Warning from 6 PM this evening to 9 am PST Sunday for West 
Entrance U.S. Waters Strait of Juan de Fuca. 


Gale Warning from 10 PM this evening to 10 am PST Sunday for 
Puget Sound and Hood Canal. 






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