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Area Forecast Discussion (AFD)

Issued by Seattle/Tacoma, WA (SEW)

FXUS66 KSEW 141042 CCA

Area Forecast Discussion
National Weather Service Seattle WA
240 AM PST Mon Jan 14 2019

.SYNOPSIS...An upper ridge over the Intermountain West will continue 
dry conditions through tomorrow with daytime temperatures above 
normal. Rain will return from the south Wednesday with temperatures 
returning closer to normal. Unsettled conditions will persist into 
the weekend.


.SHORT TERM...Upper ridging centered over northern Idaho will 
produce another sunny and mild January day across Western Washington 
after some patchy morning fog dissipates. The ridge will begin to 
weaken and shift eastward tonight. The dry conditions will continue 
on Tuesday, but high temperatures will be slightly cooler. By later 
in the day Tuesday, some high cloudiness will likely spread 
northward into the region ahead of a shortwave moving into northern 
California. This will be a hint of things to come. Some very light 
precipitation will spread into parts of Western Washington from the 
south on Wednesday as the system swings onshore, but the main effect 
will be to open the door for a large scale trough offshore to brings 
more active weather to the region in the extended period. High 
temperatures by Wednesday will cool to near or slightly above 
seasonal normals.   27

.LONG TERM...A broad upper trough will spread more widespread 
precipitation into the region on Thursday. Much like past runs, the 
Euro and GFS differ a bit on the path of the upper trough. The 00Z 
runs are close enough to make little difference in the sensible 
weather expected with rain at times Thursday into Friday. The 
Euro/GFS come into a good agreement Friday night as a weak shortwave 
ridge shifts onshore. We can might catch a short break in the precip 
then, but a warm front lifting northward will spread more rain into 
the area on Saturday with rising snow levels. A trailing cold front 
looks to sweep across the region around Sunday with snow levels 
falling back to some of the passes. 27


.AVIATION...Strong high pressure over the Intermountain west will
maintain dry and stable weather for Western Washington today and 
tonight. At the surface, offshore flow will continue with high 
pressure inland and lower pressure offshore. 

There will be areas of fog again this morning over the south 
interior. There will also be a few fog patches floating around Puget 
Sound further north and in some of the usual river valleys.
Otherwise, clear skies.

KSEA...Clear skies. Fog is expected to remain to the south this 
morning but it might get close for a few hours later this morning.
Northerly wind 5-10 knots. Schneider


.MARINE...Offshore flow will continue over the waters due to
strong high pressure east of the Cascades. Seas will build to 10 to 
12 feet today and a Small Craft Advisory for Hazardous Seas remains 
in effect for the Coastal Waters. A pair of strong Pacific frontal 
systems will reach the area Wednesday and Thursday for increasing 
S/SE flow over the waters - gales are possible. A third strong 
system may reach the area Friday night or Saturday. 33


.HYDROLOGY...Flooding is not expected in Western Washington for the 
next 7 days. 


PZ...Small Craft Advisory for hazardous seas until 5 PM PST this 
     afternoon 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.

     Small Craft Advisory for rough bar until 5 PM PST this afternoon 
     for Grays Harbor Bar.