FXUS66 KSEW 221008

Area Forecast Discussion
National Weather Service Seattle WA
208 AM PST Wed Jan 22 2020

.SYNOPSIS...Wet weather for the rest of the week into the weekend
as a series of systems moves through the area. Snow levels near
passes through today will rise steadily later Wednesday into
Thursday. Periods of heavy rain will lead to rising rivers and the
potential for river flooding later this week.


.SHORT TERM /TODAY THROUGH FRIDAY/...Showers are becoming more
scattered early this morning in wake of departing cold front. Snow
levels have lowered to around 2500 feet with heavy snow falling
yesterday evening into early this morning. Any sort of break in
between now and warm front arrival will be short lived as
precipitation shield already pushing north on Portland`s radar.
Rain, moderate to heavy at times, will reach the coast near
daybreak and push NE through the rest of the area during the
morning to early afternoon. This feature will hang up over the
area into Thursday before cold front pushes through later Thursday
into Thursday night. Snow levels will rise today from below pass
levels to 5000-7000 feet by tonight. Until snow levels rise above
passes, as cold air remains trapped in easterly flow, could see
decent amount of additional snowfall today, especially for Stevens
Pass (and Paradise and Mt Baker). Have opted to extend current
winter headlines through 4 PM today when trends can be monitored
closely. Those with travel plans over the Cascades should expect
continued hazardous winter driving conditions until the changeover
to rain.

As snow levels rise and heavy rain falls into Thursday,
flooding concerns will increase across the area. Especially heavy
amounts will fall on the favored upslode regions of the Olympics
and across the higher elevations of the Cascades. Flood Watch
remains in effect for majority of the area. See hydrology section
below for details.

In addition, winds will increase late tonight into Thursday with
gusts of 25 to 40 mph. Strongest winds expected along the coast
and the interior north of Everett.

Precipitation becomes more showery on Friday as upper level
trough swings through the area. Rain won`t be as heavy as today or
Thursday but will be enough across higher terrain to continue
flooding concerns. Snow levels will drop from around 5000 feet
during the day to around 4000 feet by Friday night so Stevens Pass
may begin to see a bit of snow again.


.LONG TERM /SATURDAY THROUGH TUESDAY/...Next system quickly brings
another round of precipitation up from the SW for Saturday. Snow
levels will be high enough for flooding concerns to remain across
much of the area with mainly rain for the passes. Active pattern
continues past Saturday with additional systems though the devil
will be in the details. Deterministic model solutions still
remain fairly chaotic with differences in timing and strength of
each system but ensemble clusters generally show large scale
troughing centered somewhere across the Pacific and ridging over
the desert SW. This would leave local area sandwiched in between
with relatively mild, moist air funneling into the area and colder
air trapped across Alaska and BC. For now current forecast lends
itself toward blended approach and has snow levels near or
slightly above pass levels. Will continue to refine over next
several days as this will certainly have implications on river



.AVIATION...Northwest flow aloft as an upper level trough moves
through this morning will transition more westerly today. A warm
front will lift north across the area today. The air mass and moist
and stable. VFR cigs early this morning with MVFR in spots across
the central and south Sound. Most sites will be MVFR by this morning
(12z-15z) with the warm front, with MVFR by this afternoon for
northern Sound. IFR will be possible as well this afternoon. Rain
will spread over the area with the front this morning. Steady rain
at times into this afternoon. Southerly sustained winds 10-15 knots
this morning will transition southeast 8-14 knots this afternoon. JD

KSEA...VFR cigs into this morning with MVFR by 14-16z as a warm
front moves through. Widespread rain this morning (after 15z)
through this afternoon. IFR possible later today. Southerly winds 10-
15 knots with gusts to 22 knots this morning, southeast winds this
afternoon from 5-12 knots. JD


.MARINE...A warm front will lift north across the area today and
shift inland Thursday into Thursday night. Small Craft Advisory
level winds for most waters into Thursday. Active weather through
this week for additional headlines as multiple systems move through
the area.

Swells 14 to 17 foot range this morning will decrease to 10-12 feet
this afternoon and through much of the week. Small Craft Advisory
for rough bar conditions at Grays Harbor for much of the week with
the magnitude of the swells. JD


.HYDROLOGY...A period of warming, rising snow levels, and heavy
rain in the mountains will force sharp rises on the rivers flowing
off the Olympics and Cascades in western Washington and increase
the risk for landslides across the area. Snow levels will rise to
around 5,000 to 7,000 feet with 3 to 9 inches of rain in the
mountains today through Saturday. Minor flooding is possible on
several rivers as a result. The Skokomish River, which may reach
moderate flood stage later today, will likely remain in flood
into the weekend. The remainder of rivers may be flowing high
through the rest of the weekend. Another period of warm and wet
weather may renew the river flooding threat early next week.


WA...Flood Watch from Thursday afternoon through Friday afternoon for
     Bellevue and Vicinity-Cascades of Pierce and Lewis Counties-
     Cascades of Snohomish and King Counties-Cascades of Whatcom
     and Skagit Counties-East Puget Sound Lowlands-Everett and
     Vicinity-Seattle and Vicinity-Southwest Interior-Tacoma
     Area-Western Skagit County-Western Whatcom County.

     Winter Weather Advisory until 10 AM PST this morning for
     Cascades of Pierce and Lewis Counties-Cascades of Snohomish
     and King Counties.

     Winter Storm Warning until 4 AM PST early this morning for
     Cascades of Whatcom and Skagit Counties.

     Flood Watch from this evening through late Thursday night for
     Admiralty Inlet Area-Central Coast-Eastern Strait of Juan
     de Fuca-North Coast-Western Strait of Juan De Fuca.

     Flood Watch through late Thursday night for Hood Canal Area-
     Lower Chehalis Valley Area-Olympics.

     Winter Weather Advisory until 4 AM PST early this morning for

PZ...Small Craft Advisory until 4 PM PST Thursday 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-Grays Harbor Bar.

     Small Craft Advisory from 10 AM this morning to 10 AM PST
     Thursday for East Entrance U.S. Waters Strait Of Juan De

     Small Craft Advisory until 10 AM PST Thursday for Admiralty
     Inlet-Northern Inland Waters Including The San Juan Islands-
     West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 10 AM this morning to 10 PM PST this
     evening for Central U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 10 AM PST this morning for Puget
     Sound and Hood Canal.




NWS SEW Office Area Forecast Discussion

Discussion Script by Ken True at Saratoga Weather - WFO Script by SE Lincoln Weather