Navigation

External Links

Alerts


No alerts 
491
FXUS66 KSEW 202252
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
352 PM PDT Tue May 20 2025

.SYNOPSIS...Cooler and showery conditions will remain across the
region today and through much of the week as a series of
disturbances cross the region. High pressure likely rebuilds
over the western U.S. over the weekend, bringing a return of
warmer and drier conditions to the area.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...Showers have
increased in coverage across Western Washington this afternoon
as the next upper level disturbance slides across the Pacific
Northwest. In addition to bursts of heavier rain and breezy
winds this afternoon, will need to continue to monitor the
potential for a isolated lightning strike or two with around a
20 percent chance of lightning across the area this afternoon.
Otherwise, a mix of partly to mostly cloudy skies and
temperatures only in the 50s to around 60 this afternoon across
the lowlands. Expect shower coverage to decrease for most
overnight, but a developing Puget Sound Convergence Zone will
likely maintain an area of steadier showers into Wednesday
morning. Some showers increase again near and south of the South
Sound later Wednesday, with lingering showers in the Cascades
late Wednesday. Transient high pressure moves overhead Thursday
with increased sunshine, drier conditions, and temperatures
returning back to near normal.

.LONG TERM /FRIDAY THROUGH TUESDAY/...The global ensembles
generally favor the development and strengthening of a ridge
over the western U.S. late in the week and into the weekend.
This is a subset, around 20%, of ensemble members that suggest
enough of a trough near the region to maintain some clouds and
mountain showers, but the majority go favor a drier trend. As a
result, the forecast continues to follow this pattern with a
warm up - most notably Sunday, with afternoon high temperatures
well into the 70s and approaching 80 in the warmest spots. It`s
worth noting that there`s is still a portion of ensemble
members that would keep temperatures much closer to (or below)
normal values. Confidence remains low into the start of next
week with some potential for the next frontal system to make
its way into the region, but the ridge may remain present and
amplified enough to keep warmer and drier conditions for first
half of next week.

&&

.AVIATION...Northwesterly flow aloft as scattered (light to
moderate) showers continue throughout the region this afternoon.
Ceilings have been gradually improving this afternoon across
the terminals. Scattered showers are expected to continue this
afternoon/evening, which could bring localized pockets of
reduced ceilings and visibility at times. Showers will gradually
taper off tonight. Isolated thunderstorms still remain in the
forecast (20-25% chance) this afternoon, however confidence
remains too low to include them in the latest TAF package. High-
res guidance shows a convergence zone may develop this evening
into early Wednesday morning along King/Snohomish counties
(along KPAE). Ceilings will drop to MVFR Wednesday morning along
the majority of Puget Sound terminals (KPWT may drop down to
IFR) and northern interior terminals, with improvement expected
late in the morning. Otherwise, VFR expected to persist for the
majority of the TAF period.

Breezy S/SW winds along interior terminals will continue this
afternoon 10-15 kt and gusting to 20-25 kt, subsiding overnight to 5-
7 kt. Surface flow will shift more northerly late Wednesday morning.

KSEA...Scattered showers continue around the terminal this
afternoon. However, any showers that do impact the terminal may
briefly reduce ceilings and visibility at times. Models are still in
general agreement for convergence zone development to stay north of
the terminal tonight. Guidance is hinting at high-end MVFR ceilings
between 12z-17z Wednesday morning, with improvement into VFR
expected late morning. Otherwise, VFR is favored for the majority of
the TAF period.

S/SW breezy wind continue this afternoon at 10-15 kt and gusting up
to around 20 kt. Winds are expected to subside tonight. Surface
winds will shift north/northeasterly late Wednesday morning into the
afternoon (6-8 kt).

29

&&

.MARINE...Westerly surface flow along the coastal waters will shift
more northwesterly this evening. A weak push along the Central and
East Strait is expected tonight. Sustained wind speeds will be
around 15-20 kt, but probabilistic guidance highlights a 60-80&
chance of wind gusts reaching small craft criteria for a brief
period, for which a Small Craft Advisory has been issued. In
addition, a Small Craft Advisory remains in effect for the coastal
waters and West Strait for high seas 10-11 ft this afternoon. Seas
should subside below 10 ft tonight into early Wednesday morning.

Weak high pressure will build over the coastal waters on Wednesday
and Thursday. The next frontal system looks to arrive on Friday,
with high pressure rebuilding over the weekend.

Seas 9 to 11 ft this afternoon and will subside late tonight to 7 to
8 ft. Seas look to remain below 10 ft through the rest of the week.

29

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 6 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-Grays Harbor Bar-
     West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 8 PM this evening to 2 AM PDT
     Wednesday for Central U.S. Waters Strait Of Juan De Fuca-
     East Entrance U.S. Waters Strait Of Juan De Fuca.

&&

$$

NWS SEW Office Area Forecast Discussion