Weather Service Report


118 
FXUS66 KSEW 241659
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
859 AM PST Sat Feb 24 2018

.SYNOPSIS...Cool and unsettled weather will continue through the
end of next week. Next system arriving tonight into Sunday. Low
level onshore flow ahead and with the system will lift the snow
levels above the surface. A brief break in the action on Monday
before the next system arrives Monday night and Tuesday. A much 
wetter system will arrive Wednesday night or Thursday.

&&

.SHORT TERM...A weather system will exit the area this morning.
Snow over the mountains will taper. The winter weather advisory is
scheduled to end at noon today and that looks on track. A Puget
Sound Convergence Zone sagging south through central Puget Sound 
should break up later this morning. Outside of the convergence 
zone, the lowlands will be mostly dry today in between weather 
systems. There will even be some sun breaks.

Another frontal system will move into the area later tonight and
push inland on Sunday. Snow levels will be low but onshore flow
should keep it warm enough for just cold rain in the lowlands. 
The Cascades will get a lot of snow - probably one to two feet.
The winter storm watch will be updated to a warning this morning.
There will probably be another PSCZ behind the frontal system 
later Sunday. 

An upper trough will settle over the area Sunday night and then
push a bit inland on Monday. A threat of lowland snow will return
again late Sunday night/early Monday morning as snow levels lower
to near sea level. However, most of the area will be dry by then 
with just isolated showers. New snow accumulations, if any, 
should be light and isolated. Schneider

.LONG TERM...Previous discussion...Extended models in pretty good
agreement this morning with yet another system embedded in the 
northwest flow aloft moving over the area Monday night into 
Tuesday. 00z model runs a little wetter, warmer and stronger with 
the next front arriving Wednesday night into Thursday. Cool upper 
level trough moving back over the area Thursday night into Friday 
with another low snow level scenario with showers. Felton

&&

.AVIATION...Moderate northerly flow aloft today will turn westerly 
tonight. At the surface, onshore flow today will increase tonight 
after a front moves through the region. The air mass will be moist 
with scattered rain or mixed rain and snow showers. A convergence 
zone over King County this morning will dissipate by noon.

Ceilings are generally MVFR or IFR over the interior, with VFR or no 
ceilings over western sections. A weather system will bring MVFR 
ceilings with rain to all areas tonight. 

KSEA...Currently VFR conditions, but a weakening convergence zone 
just north of the terminal this morning could bring MVFR ceilings 
and MVFR visibilities in a mixed rain/snow shower. The convergence 
zone will dissipate by noon. VFR conditions after that, becoming 
MVFR after 06Z as rain develops. Southerly wind 8-12 kt today 
increasing to 15-25 kt tonight. CHB

&&

.MARINE...Onshore flow will ease today, then increase tonight after 
a front moves through the area. Small craft advisories are in effect 
for most waters this morning. A gale watch is in effect for the 
coast and strait tonight through Sunday. 

Weak high pressure over the area Monday will be followed by another 
front on Tuesday. CHB

&&

.HYDROLOGY...River flooding is not expected for the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory until noon PST today for Cascades of 
     Pierce and Lewis Counties-Cascades of Snohomish and King 
     Counties-Cascades of Whatcom and Skagit Counties.

     Winter Storm Warning from 7 PM this evening to 7 PM PST Sunday 
     for Cascades of Pierce and Lewis Counties-Cascades of 
     Snohomish and King Counties-Cascades of Whatcom and Skagit 
     Counties.

PZ...Gale Watch from late tonight through Sunday 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-West Entrance U.S. 
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory until midnight PST tonight for Central U.S. 
     Waters Strait Of Juan De Fuca-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-East Entrance U.S. Waters Strait Of Juan De Fuca-West 
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory for rough bar until 6 AM PST Sunday for 
     Grays Harbor Bar.

     Gale Watch from late tonight through Sunday afternoon for 
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance 
     U.S. Waters Strait Of Juan De Fuca.

&&

$$

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