Flash Flood Warning 1, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
904 PM PDT Mon Oct 24 2022

.SYNOPSIS...Showers will linger over portions of Western Washington
tonight before a second weather system moves through the area
Tuesday and Tuesday night. Another system will move by mainly to the
north Wednesday. Additional fronts will arrive Thursday through the
weekend for continued wet and windy weather at times.

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.SHORT TERM /TONIGHT THROUGH THURSDAY/...Satellite imagery shows
two convergence zones over Western Washington. One in the usual
location, just south of the King/Snohomish county line in Northern
King county and another one over Whatcom and Skagit county. This
convergence zone is caused by the northwesterly winds flowing out
of the Strait of Georgia. Both zones have produced lightning in
the last hours along with brief heavy downpours and a bit of hail.
Outside the convergence zones just some isolated showers left
mainly along the west slopes of the Olympics. It's a little cool
out there this evening with temperatures in the mid 40s to lower
50s at 8 pm/03z.

Convergence zone shower/thunderstorm activity will come to an end
after midnight. A short break in the action early Tuesday morning
before rain out ahead of the next system moving down the British
Columbia coast reaches the coast Tuesday morning. Rain  spreading
inland late morning/midday. Front moving through in the evening hours.
Not much cold air behind the front with most of the shower
activity early Wednesday morning in a convergence zone over
Snohomish county. Weak upper level ridge trying to build in later
Wednesday but a weak warm front moving over the top of the ridge
will keep a chance of rain in the forecast. Another front arriving
Thursday for more rain. Current forecast has the trends covered.
Felton

.LONG TERM /FRIDAY THROUGH MONDAY/...Previous discussion follows.
Active weather persists into the long term although there may be
a brief quiet period Friday as a very weak upper level shortwave
ridge tries to develop. Operational GFS appears to be the driest
and operational ECMWF suggests that the southern half of the CWA
may be dry, but ensembles are not sold on the prospect, showing
varying amounts of precip, albeit generally on the low side. An
interesting scenario arises late Friday/early Saturday where the
convergence of two systems may allow for the first atmospheric
river event of the season. ECMWF does not share the GFS view of
this though as it brings the systems into W WA in a more
sequential fashion. Ensemble members are scattered on the matter
lowering any confidence in either solution. Additional fronts
Sunday and Monday, one right after the other, will keep conditions
quite moist of W WA for the remainder of the forecast cycle.

High temps for the remainder of the forecast period hover right
around seasonal normals, generally in the mid to upper 50s. 18

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.AVIATION...VFR to MVFR ceilings are being observed across western
Washington tonight, with radar still showing showers across
portions of the area. The heaviest showers continue across far
northern counties of the Sound (mainly impacting KBLI) and along
a CZ just to the east of the Sound. The coverage of showers
should continue to decrease overnight, however cannot rule out
some temporary lowered ceilings for terminals in the vicinity of
any lingering heavier showers. Overall, expect ceilings to rebound
to widespread VFR conditions overnight and into Tuesday, before
lowering back down to widespread MVFR Tuesday afternoon and
evening as the next system approaches. SW winds between 5-10 kt
overnight (W winds 5-15 kt through Strait of Juan de Fuca
including KCLM). WNW flow aloft.

KSEA...Conditions generally VFR. VFR conditions should persist
overnight as showers taper across the region. Winds are south-
southwest winds between 5-10 kt persisting into Tuesday morning,
before increasing to 7-12 kts Tuesday afternoon.

McMillian/Borth

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.MARINE...A series of frontal systems will push through the area
waters this week. Today's front has pushed through the area
waters but headlines remain in its wake for breezy winds and
hazardous seas. Thus, SCAs are posted for all waters but should
expire gradually overnight into Tuesday morning. Winds are to
decrease briefly into Tuesday but the next disturbance in line
will track through Tuesday night into Wednesday morning. This
feature is on tap to bring an additional round of area headlines.
A potentially stronger system may then impact the area on Thursday,
possibly bringing gales and high-end SCA to the waters along with
hazardous seas. A brief reprieve is expected on Friday before
more disturbances arrive over the weekend.

Elevated seas up to 12-16 feet tonight should gradually subside
into Tuesday, but remain above 10 ft through Wednesday. Seas
could again increase to above 15 ft on Thursday and look to
likely remain hazardous into the weekend.

McMillian/Borth

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.HYDROLOGY...No river flooding is expected for the next 7 days.
However, with the potential for heavy rain with each of the next
few frontal systems over the next week, there is some concern for
potential burn scar debris flows in the recently burned areas.

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.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory until 5 AM PDT Tuesday for West Slopes
     North Cascades and Passes.

     Flash Flood Watch through Tuesday afternoon for West Slopes
     North Central Cascades and Passes.

PZ...Small Craft Advisory until 11 AM PDT Tuesday 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-West Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 8 AM PDT Tuesday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory until 5 AM PDT Tuesday for Admiralty Inlet-
     Northern Inland Waters Including The San Juan Islands.

     Small Craft Advisory until midnight PDT tonight for Puget Sound
     and Hood Canal.

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