Tornado in Washington, October 18, 2019

Area Forecast Discussion
National Weather Service Seattle WA
306 PM PDT Fri Oct 18 2019

.SYNOPSIS...A series of weather systems will move through Western
Washington into the first half of next week. A brief break in the
action is possible Wednesday and Thursday as a ridge begins to
build offshore.

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.SHORT TERM /TONIGHT THROUGH MONDAY/...Radar as of 2PM shows
scattered showers across Western Washington this afternoon with an
Olympic rain shadow effect over portions of northern King County
and Snohomish County with westerly flow aloft. A few lightning
strikes have been recorded through today, generally over the
coastal waters. Any thunderstorm activity should be over the coast
through this afternoon into early tonight as an upper level
trough approaches.

A heavier batch of precipitation will slide through tonight,
especially across the southern portions of the CWA generally south
of King County, as the upper level trough moves through. Snow
levels will fall near 4000 feet by Saturday morning. Winter Storm
Warning is in effect for the Cascades of Lewis and Pierce Counties
through Saturday afternoon where an additional one to two feet of
snow is possible in spots. A Winter Weather Advisory is in effect
for the Northern and Central Cascades of Western Washington where
an additional 4 to 8 inches is possible above 4000 feet. Snow
will taper off by later on Saturday.

Isolated thunderstorms will also be possible later tonight through
Saturday afternoon as the trough slides through. Best chance for
t-storms across the interior around the Puget Sound will be
midday Saturday through the afternoon generally south of Skagit
County with sufficient instability and lifted indices. A
convergence zone may also develop over Snohomish and King counties
Saturday afternoon into Saturday evening. If the PSCZ does form,
locally higher precipitation amounts, including snowfall over the
Cascades, will be possible with convective banding. Otherwise some
sunshine may be around Saturday afternoon, though will be limited
with extensive cumulus clouds. Temperatures on Saturday will be in
the 50s across the area.

A brief break in between systems is expected Saturday night but
another system will slide through Sunday morning into the
afternoon. Snow levels will rise with this system generally above
5000 feet by the afternoon. Another system will then move through
on Monday. Temperature Sunday and Monday will be in the mid to
upper 50s across the area. JD

.LONG TERM /TUESDAY THROUGH FRIDAY/...An upper trough will
generally slide north of the area on Tuesday with chance of POPs
around through the afternoon. Guidance does suggest an upper level
ridge builds offshore Wednesday into Thursday for drier weather.
Temperatures in the mid to upper 50s across Western Washington
through the end of the week. JD

&&

.AVIATION...An upper level trough will approach the region
tonight. The flow aloft is westerly and the air mass is moist and
slightly unstable. Current ceilings across the region are a mixed
bag as of 245 PM and range from VFR to MVFR/IFR in areas where
heavier showers are moving through. Radar imagery currently shows
showers moving in over much of the region, with a slight rain
shadow over the central portion of the Sound. A few thunderstorms
remain possible for the coastal waters and could still impact the
coastal terminals this afternoon into early this evening. Expect
showers to increase in coverage throughout the remainder of the
afternoon and evening hours, with ceilings ranging from VFR in
rain shadowed areas to MVFR/IFR in areas in the vicinity of
heavier precipitation.

KSEA...Current conditions MVFR with light rain falling at the
terminal. Could see ceilings improve again by late afternoon or
early evening as showers move off to the east, but then lower
again tonight as additional showers move through the region.
Surface wind southerly at 5 to 10 knots. SB

&&

.MARINE...Small craft advisories remain in place across the
coastal waters, northern inland waters, Admiralty Inlet and Puget
Sound this afternoon as a system makes its way through the region.
The small craft for hazardous seas will continue for the coastal
waters through this evening, with seas gradually subsiding back to
10-15 feet later tonight. A small craft for rough bar will also
continue for Grays Harbor Bar through Saturday afternoon. Have
added a small craft advisory for the Strait of Juan de Fuca for
Saturday associated with a westerly push. Active weather will
continue into next week with additional headlines likely from time
to time. SB

&&

.HYDROLOGY...A series of wet systems moving through the area into
early next week will cause rivers to rise. As such, the Skokomish
will need to be monitored. Otherwise...river flooding is unlikely
over the next seven days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Storm Warning until 6 PM PDT Saturday for Cascades of
     Pierce and Lewis Counties.

     Winter Weather Advisory from 6 AM to 6 PM PDT Saturday for
     Cascades of Snohomish and King Counties-Cascades of Whatcom
     and Skagit Counties.

PZ...Small Craft Advisory from 11 PM this evening to 8 PM PDT
     Saturday 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 hazardous seas until 11 PM PDT this
     evening 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 PDT Saturday for
     Grays Harbor Bar.

     Small Craft Advisory from 2 PM Saturday to 2 AM PDT Sunday for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 2 AM PDT Saturday for Northern Inland
     Waters Including The San Juan Islands.

     Small Craft Advisory from 2 PM to 8 PM PDT Saturday for West
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 8 PM PDT this evening for Admiralty
     Inlet-Puget Sound and Hood Canal.

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