000
FXUS66 KSEW 211011
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
211 AM PST Tue Jan 21 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 today into Wednesday 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 THURSDAY/...Off to the races this
morning as we head into an active rest of the week. First in a
series of systems is moving onshore early this morning with rain
overspreading the coast and Olympic Peninsula. Rain will continue
to spread inland through the morning hours with showers continuing
into Wednesday morning as cold front passes through. Snow levels
will be around 2500-3500 feet for majority of the moisture
associated with the system. Have included the Olympics in a winter
weather advisory. Otherwise going headlines remain in place.
Hazardous travel is expected over the passes so those with travel
plans should keep an eye on WSDOT road conditions
(wsdot.com/travel/passes). Snoqualmie Pass may see a changeover
to rain or rain/snow mix tonight as current easterly flow becomes
more westerly. Winds will also pick up today with breezy
conditions across the lowlands on the order of gusts of 25 to 40
mph - current forecast is below advisory criteria.

In addition, hi-res guidance indicates enough instability across
the coastal waters and immediately inland to continue mention of
thunderstorms this morning through early afternoon. Any convection
that fires will be capable of heavy downpours and small hail.
Activity should wane later this afternoon as trough axis passes to
the west. Current forecast aligns well with Storm Prediction
Center general thunder outlook.

Little noticeable break in the action during the day Wednesday
into Wednesday night as warm front associated with our next
system pushes north across the area. Cold front will follow on
Thursday with another round of breezy winds. As warm, moist air
pushes in, snow levels will rise steadily and be above pass levels
by Wednesday evening. A few more inches likely for pass levels
though at the onset. Otherwise, from here on out, heavy rain up to
around 5000-6000 feet becomes the main concern. With this system,
heaviest amounts will fall over the Olympics and Cascades with a
bit of a rain shadow across the northern inland waters and
portions of the Sound. Rivers flowing off the mountains will see
rapid rises and may begin to see minor flooding as early as
Thursday night into Friday morning. See hydrology section below
for details.

CEO

.LONG TERM /FRIDAY THROUGH MONDAY/...Additional systems arrive
Friday into the weekend. Past Friday, uncertainty rises in the
details, especially with precipitation amounts and breaks in
between systems. Entire period likely won`t be a washout but flooding
concerns will continue as additional rainfall will enhance river
rises. Temperatures will remain on the mild side with afternoon
highs in the lowlands topping out in the upper 40s to low 50s.

CEO

&&

.AVIATION...Southwesterly flow aloft as an upper level trough moves
over the area. The air mass is moist and stable. Light rain
spreading across the Puget Sound early this morning will slide east
over the next few hours. Convective showers following the front this
afternoon. VFR cigs into the morning will transition to MVFR this
afternoon. Winds will increase through the morning with the front.
Southerly wind gusts up to 25-29 knots by this afternoon. JD

KSEA...VFR cigs will transition to MVFR late this morning through
the afternoon. East winds till 12z with southerly winds through the
afternoon, gusts up to 25 knots this afternoon. JD

&&

.MARINE...A front will move through through today with gales
expected for the coastal waters and possibly the Central and Eastern
Strait of Juan de Fuca. Gale Warning issued for the Northern Inland
Waters through this afternoon with strong southerly winds. Small
Craft Advisory level winds elsewhere with the front. Swells will
increase through today with swells 15-21 feet by this afternoon.
Active weather through this week as multiple systems move across the
waters. SCA winds and gales possible with the systems. 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. Snow levels
will rise to around 5,000 to 6,000 feet with 3 to 6 inches of rain
in the mountains Wednesday through early Friday. Minor flooding
is possible on several rivers as a result. Rivers may be flowing
high through the weekend.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory until 4 AM PST Wednesday for Cascades of
     Pierce and Lewis Counties-Cascades of Snohomish and King
     Counties.

     Winter Storm Warning until 4 AM PST Wednesday for Cascades of
     Whatcom and Skagit Counties.

     Winter Weather Advisory until 4 AM PST Wednesday for Olympics.

PZ...Small Craft Advisory from 4 PM this afternoon to 4 AM PST
     Wednesday 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.

     Gale Warning until 4 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 until 10 AM PST Wednesday for Grays Harbor
     Bar.

     Gale Warning until 7 PM PST this evening for Central U.S. Waters
     Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of
     Juan De Fuca-Northern Inland Waters Including The San Juan
     Islands.

     Small Craft Advisory until 4 PM PST this afternoon for West
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 4 AM PST Wednesday for Admiralty
     Inlet-Puget Sound and Hood Canal.

&&

$$

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NWS SEW Office Area Forecast Discussion

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