854
FXUS66 KSEW 042126
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
226 PM PDT Sat May 4 2024

.SYNOPSIS...Cool and unsettled weather will continue over western
Washington into early next week. A pattern shift can be expected
by midweek as upper level ridging builds over our region, bringing
drier and a much warmer conditions to our area.

&&

.SHORT TERM /TONIGHT THROUGH TUESDAY/...Latest water vapor imagery
shows a broad area of low pressure sinking southward into the
Oregon and California border, continuing to push showers through
our area. The boundary continues to make little progress, so
expect maybe some lighter rain for more interior locations
through this evening..along with areas up to the north in Whatcom
county remaining mostly dry. Most of the rain this evening will be
focused along the coast, the Olympia Peninsula, and Olympia
southward as thats where the boundary is focused. High
temperatures this afternoon hovering in the 50s, while areas in
Whatcom County will experience a touch warmer temps, in the low
60s.

The broad area of low pressure associated with an upper level
trough will continue to move eastward inland on Sunday, but will
still remain close enough to continue showers for western
Washington. With another trough right behind it, onshore flow will
be strong Sunday providing more wetter conditions, especially for
interior locations. Along with rain showers throughout the
interior, some snow can be expected in the higher Cascades..
generally around 4000 to 5000 feet, but will be rather light.

As the upper level trough crosses the region into Monday, cooler
air aloft will help produce some instability along with steep
lapse rates, which could help the development of some isolated
thunderstorms over the interior into Monday afternoon. Strong
onshore flow will continue as well, also prompting the development
of a potential Puget Sound Convergence zone into Monday evening.

Unsettled showery conditions look to continue through Tuesday and
Wednesday as the upper level trough lingers over the region.

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...There is strong support
from ensemble guidance that a pattern shift is upon western
Washington, with an upper level ridge building over the region
starting on Wednesday. Although there are some small variations in
timing and placement of the upper level ridge, there is a general
agreement that much warmer and drier conditions will take place
throughout much of the long term, with NBM high temperatures in
the lowlands around mid to upper 70s into Friday and Saturday.

Mazurkiewicz

&&

.AVIATION...An upper low will move into the Oregon California border
this evening with southeasterly flow aloft transitioning westerly on
Sunday. Generally VFR north of SEA this afternoon with MVFR/IFR
across the coast and southern Puget Sound. Cigs will slowly lower
for areas of central Puget Sound this evening into tonight, with
most areas in MVFR/IFR cigs by Sunday morning. Light rain will
continue at times into early tonight, with another round of lighter
rain on Sunday. Some improvement to cigs by Sunday afternoon, but
generally MVFR to low-end VFR expected. A northerly component to the
winds this afternoon will transition more southerly this evening,
with southerly winds increasing tonight.

KSEA...VFR mid clouds this afternoon with periods of light rain.
Cigs will slowly lower this evening to MVFR generally between 01-
03z. Cigs will remain low-end MVFR with potentially periods of IFR
tonight into Sunday morning. Cigs generally remain MVFR Sunday
afternoon with light rain at times. Northerly winds will transition
more southwesterly this evening, mainly between 00-02z. Southerly
winds will then increase into Sunday morning. JD

&&

.MARINE...A frontal system will move through the southern portions
of the waters into this evening. Another weather system will move
across the waters Sunday night into Monday. A northerly component to
the winds this afternoon will transition more southerly tonight into
Sunday. A westerly push through the central and eastern Strait of
Juan de Fuca tonight will result in brief SCA wind gusts. West winds
then increase through the Strait of Juan de Fuca again Sunday
afternoon into early Monday for another round of SCA winds. Winds
may also reach SCA for adjacent areas, including Admiralty Inlet and
northern inland waters, south of the San Juan Islands, during this
period. In addition, winds will increase Sunday afternoon into
Monday morning for Puget Sound with an increased likelihood of SCA
wind gusts during this period.

Additional westerly pushes through the Strait of Juan de Fuca are
likely Monday and Tuesday evening. Winds will then transition more
northerly Wednesday into late week as high pressure builds into the
area.

Seas of 5 to 8 feet will continue into Monday before building to 9
to 12 feet Monday night through Tuesday. JD

&&

.HYDROLOGY...No river flooding is expected over the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 6 PM this evening to 8 AM PDT Sunday
     for Central U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 6 PM this evening to 5 AM PDT Sunday
     for East Entrance U.S. Waters Strait Of Juan De Fuca.

&&

$$