Gale Warning 52, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
1007 AM PDT Thu Sep 24 2020

.UPDATE...Isolated convection across the region this morning as
Western Washington remains in a post-frontal unstable environment.
Radar depicts thunderstorms moving onshore along the Pacific coast
and across the higher terrain of the Olympics and central
Cascades. A few storms had even started to make their way into
the Sound at this hour. Most recent meso-analysis depicts the
most favorable environment for thunderstorms offshore and along
the coast this morning. However, given instability and clearing
trend on satellite, expect daytime heating to aid in additional
thunderstorm development across the area this afternoon. Thus,
will continue to watch the radar trends throughout the day. Small
hail, gusty winds, and brief heavy downpours will be possible in
any stronger storms. The previous discussion follows, with updates
made to the marine and aviation sections. 14

&&

.SYNOPSIS...A series of vigorous frontal systems will bring wet
and windy weather at times along with cooler temperatures through
Saturday. High pressure aloft will build over the region the
first half of next week for a return of dry and warmer weather.

&&

.SHORT TERM /TODAY THROUGH SATURDAY/...Showery weather will
continue today with isolated thunder possible as a broad upper
trough traverses the area. Highs will be mostly in the mid 60s.

A vigorous frontal system will move through the area later
tonight and Friday bringing another shot of rain. An associated
deep surface low will track inland over Vancouver Island Friday
morning for another round of windy conditions, especially coast
and Northwest Interior. It looks at least as windy as the system
yesterday and maybe a notch higher. There will also be a good
onshore push behind the front later Friday for gusty southerly
winds in Puget Sound. Highs will be in the lower to mid 60s.

Models and ensemble forecasts are now drier on Saturday as an
upper ridge starts to build in from the west. There is enough
uncertainty that likely PoPs are still in the forecast for now but
the trend seems to be for drying. Highs will still be slightly
below normal - mostly in the 60s. Schneider

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...An upper ridge will build
over the area on Sunday. This will continue the drying trend with
most of the rain pushed north of the area. The upper ridge will
continue to build over the region Monday and Tuesday with low
level offshore flow developing. This will dry things out entirely
and allow highs to warm into the 70s. More of the same is expected
for Wednesday: a strong upper ridge over the area and low level
offshore flow resulting in dry weather and highs generally in the
70s. Schneider

&&

.AVIATION...Scattered showers will continue through the day. While
terminals will generally remain VFR, these showers will bring
temporary lowering of ceilings/visibility. Strongest of these could
produce some lightning, though confidence in any particular
terminal generally remains low. Will handle VCTS/TS with
amendments as trends dictate. Otherwise, breezy south winds with
gusts to 25 kt, and stronger winds developing after 06z near the
coast and closer to 12z inland.

.KSEA...VFR conditions this morning likely continue, though periods
of MVFR conditions showers are expected at times. A thunderstorm
could develop in vicinity of terminal this afternoon, but confidence
in developing/timing remains low South winds around 15 kt with gusts
20-25 through the day. Stronger south wind arrives around 12z.

Cullen

&&

.MARINE...Yesterday's frontal system is located well east of the
local area this morning, with area waters within an unstable post-
frontal environment. Widely scattered showers are being detected on
local radar imagery this morning and are expected to affect all
waters through the day today. Isolated lightning strikes are also
embedded within some of the stronger showers. This too will remain a
possibility through the day today over all waters.

Winds have eased since yesterday, but still remain breezy across
most waters this morning, esp across the Coastal Waters, Admiralty
Inlet, Puget Sound, and the Northern Inland Waters. A Small Craft
Advisory Covers this and will continue through the day. Elsewhere, A
Small Craft Advisory is in place for the Western Strait of Juan de
Fuca and Grays Harbor Bar where seas remain hazardous.

The next in a series of storm systems will quickly move into the
area late tonight and early Friday. Winds will noticeably pick up,
especially offshore where a Gale Watch is now in effect. Expect a
period of breezy to windy conditions across all waters as this
system pushes through during this time frame. The other threat will
be the large swell making for hazardous seas offshore. Expect swells
of generally 14-16 feet to begin early this morning and continue
through Friday afternoon. A High Surf Advisory will also remain in
effect to account for this.

Additional systems will affect the area this weekend, but are
expected to be weak in comparison to this week's systems. Drier and
more tranquil weather is expected for much of next week.

Kovacik

&&

.HYDROLOGY...A vigorous frontal system will bring another round
of heavier rainfall later tonight and Friday. River flooding is
not forecast at this time but additional rises to many rivers is
expected - particularly those draining from the Olympics and North
Cascades. An additional 3-5 inches of rain is likely over the
mountains with this frontal system tonight and Friday.

A drying trend will begin over the weekend with some light rain
lingering in spots. Dry weather will return early next week.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...High Surf Advisory until 2 PM PDT Friday for Central Coast-North
     Coast.

PZ...Gale Watch from late tonight through Friday morning 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 2 AM PDT Friday 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 from 8 AM to 11 PM PDT Friday 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 11 PM PDT Friday for Grays Harbor Bar-
     West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 2 AM to 8 AM PDT Friday for East
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 9 AM PDT Friday for Admiralty Inlet-
     Northern Inland Waters Including The San Juan Islands-Puget
     Sound and Hood Canal.

&&

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