Forecast Discussion
Forecast Discussion for SEW NWS Office
468
FXUS66 KSEW 192040
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
140 PM PDT Mon May 19 2025
.SYNOPSIS...A frontal system has moved east of the area today,
leaving scattered showers and a possible rumble of thunder
through the rest of the day. Another round of showers or
isolated thunderstorms will be possible Tuesday before shower
chances decrease through the week and temperatures warm.
&&
.SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/...
The upper level trough/low that sent the frontal system across
Washington today has stalled along the BC coast. This low will
eject another wave across the area this evening into early
Tuesday bringing another uptick in shower activity. A third,
weaker wave will then slide through the area as the low weakens
late Tuesday into early Wednesday. This parade of waves will
keep showers and low-end chances of weak thunderstorms in the
forecast through late Tuesday.
By Wednesday an unrelated compact wave will move across the
west coast generally across northern CA and OR, perhaps glancing
the southern Cascades.
&&
.LONG TERM /THURSDAY THROUGH MONDAY/...
Weak split flow aloft will keep the area fairly seasonable
Thursday into Friday. Chances for weak afternoon showers, mainly
over the mountains, cannot be ruled out. Temperatures should
warm 2-4 degrees in most areas, but still generally in the 60s
across most of the region.
By the weekend, the longwave pattern amplifies with ridging over
the western US and troughing across the eastern Pacific. This
should allow temperatures to warm a few more degrees Saturday.
For Sunday and particularly Monday, there is a massive range of
potential outcomes in how and when this pattern breaks down.
For example, in terms of temperature there is a 10th-90th
percentile range of 60-81 degrees for KSEA. This also has
ramification for precipitation chances.
-Wolcott-
&&
.AVIATION...Troughing will be across Western Washington into Tuesday
for continued westerly flow aloft. Onshore flow continues at the
surface.
Generally VFR cigs this afternoon with scattered showers,
particularly over the Olympic Peninsula. Localized MVFR cigs also
continues along the coast this afternoon. VFR cigs to continue for
most interior sites into tonight. Cigs will likely lower towards
MVFR Tuesday morning, with MVFR or low-end VFR expected for most
Tuesday AM. Localized LIFR/IFR is possible around PWT. VFR cigs
again Tuesday afternoon with showers at times. Breezy SW surface
winds this afternoon, particularly at PAE, BFI, PWT, and SEA. Winds
will remain locally breezy through this evening before slowly
tapering a bit further later tonight. S/SW winds Tuesday.
KSEA...VFR cigs into tonight. Cigs will lower towards MVFR Tuesday
morning (generally after 12-13z), with approximately a 30%
probability of MVFR cigs through 19z Tuesday. VFR Tuesday afternoon.
A few showers may be around at times through Tuesday. Breezy SW
surface winds through this evening, with gusts of 20 to 25 kts.
Winds will subside a bit tonight. JD
&&
.MARINE...Onshore flow continues following a frontal system that
moved across Western Washington this morning. Small Craft Advisory
winds will continue into this evening due to gusts ranging 20 to 25
kts around Puget Sound. SCA west winds also expected into this
evening for the outer Coastal Waters. Winds will then slowly subside
tonight across the waters. A weak westerly push is expected through
the Strait of Juan de Fuca Tuesday evening, but at this time, winds
are expected to remain below SCA threshold. Weak high pressure will
then build over the area Wednesday into Thursday. A weakening system
may approach the area on Friday before high pressure builds again
further over the weekend.
Seas will build to 9 to 13 feet for the Coastal Waters tonight
through Tuesday. Seas will then subside below 10 feet Tuesday night
and subside to 4 to 6 feet by midweek. JD
$$
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 2 PM PDT this afternoon for East
Entrance U.S. Waters Strait Of Juan De Fuca-Northern
Inland Waters Including The San Juan Islands.
Small Craft Advisory until 11 PM PDT this evening for Puget
Sound and Hood Canal.
Small Craft Advisory until 6 PM PDT Tuesday for Coastal Waters
From Cape Flattery To James Island 10 To 60 Nm-Coastal
Waters From Cape Flattery To James Island Out 10 Nm-
Coastal Waters From James Island To Point Grenville 10 To
60 Nm-Coastal Waters From James Island To Point Grenville
Out 10 Nm-Coastal Waters From Point Grenville To Cape
Shoalwater 10 To 60 Nm-Coastal Waters From Point
Grenville To Cape Shoalwater Out 10 Nm.
&&
$$
NWS SEW Office Area Forecast Discussion