697
FXUS66 KSEW 152138
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
238 PM PDT Wed May 15 2024

.SYNOPSIS...High pressure remains offshore of Washington,
providing one more day of mostly clear skies and above average
temperatures across Western Washington today. By Thursday, an
upper level trough will dig down into the region from Canada. This
will return a chance of showers for most of the outlook area
Thursday. A cool and damp pattern is expected to persist from this
weekend into next week, with below average temperatures and
several chances for showers.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY/...One more mostly sunny day
is panning out across the outlook area today. An upper level
ridge/high pressured centered off the coast still remains through
today. Satellite imagery shows some high cirrus across the entire
area, with a few cumulus over the Cascades and Olympics. A cumulus
cloud band remains off the coast, thanks to the northwest flow
aloft and near the surface. Temperatures have climbed into upper
60s and low 70s in most of the lowlands this afternoon (helped by
light winds and maximum daytime heating). This part of the
forecast remains largely on track, and a few areas will likely
peak into the mid 70s this afternoon.

By Thursday, an upper level trough swings around a low deep in northern
Canada. This will dip a jet streak/vorticity max down into
Washington for Thursday, as well as breaking down the high over
the Pacific. Down at the surface, a cold front will swing through
with this shortwave during the day. Due to limited moisture
available with this front, precipitation is expected to remain
limited with shower activity across the area. The heaviest of the
showers are expected to be in the northern Cascades. QPF amounts
there range from around a quarter to a half an inch, with
just several hundredths in the lowlands. With the cooler air
coming through, snow levels will drop to around 3500 feet Thursday
afternoon. Additionally, the onshore flow behind the front may
result in a convergence zone over western Snohomish/Skagit
counties. Breezy southwest/west winds at 10 to 15 mph are possible
post-front in the lowlands, with gusts to 20 mph possible.

The Thursday trough will depart the region Friday, leaving the
remainder of the day dry with high temperatures only peaking in
the low to mid 60s. Clouds will break up some for the afternoon.
Another shortwave trough appears to dip into Washington on
Saturday. This will return the chance of showers (with best chance
again being east of I-5 in the Cascades). NBM was giving a brief slight
chance of thunder in the northern Cascades for the afternoon, with
the cooler air aloft. Temperatures for Saturday slightly will be
slightly cooler, with upper 50s to low 60s. Winds will diminish
going into Friday/Saturday.

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...There is better agreement
now between the ensemble clusters and deterministic models for
early next week. It appears the pattern will be influenced by
cool and unsettled weather via a trough over the northwest. Flow
will be northwesterly, which will keep temperatures at or below
average for the first part of the week. Shower chances will be
possible via several shortwaves first part of Sunday, and Monday
through Wednesday. None of these days appear to be washouts at
this point, with coverage being spotty and confined to primarily
the mountains. The NBM again mentioned thunder for the northern
Cascades on Monday.

HPR

&&

.AVIATION...Northwesterly flow aloft through Thursday morning with
upper-level ridging aloft. Flow aloft will then shift more westerly
by Thursday evening as a shortwave trough rounds the area.

VFR across western Washington as high clouds stream over. VFR
conditions expected to remain in place for most terminals for the
remainder of the day, however will see cigs gradually lower from
west to east throughout the night in response to an upcoming system
on Thursday. By 12z Thursday, stratus will be widespread across area
terminals with MVFR in the cards. Can`t rule out localized IFR and
LIFR for terminals such as HQM. Some brief improvement to low-end
VFR is possible into Thursday afternoon but rain showers and
convergence zone activity is likely to hang around.

KSEA...VFR with high cirrus currently. But as mentioned, MVFR is
possible going into early Thursday morning as stratus fills in
around 09-12z. Rain showers and convergence zone activity is
possible into Thursday also.

McMillian

&&

.MARINE...A round of SCA level winds expected in the Strait of Juan
de Fuca starting this afternoon and look to continue into Thursday
as a front passes. A stronger push is expected to accompany an
incoming frontal system Thursday night and Friday which may need yet
another set of headlines. A SCA has also been issued for the coastal
waters, associated with the aforementioned front Winds expected to
ease for most areas, save perhaps the outer coastal waters this
weekend into early next week.

Seas will hold around 4 to 6 ft through Thursday before increasing 8
to 12 ft from Friday into the weekend, reducing to 6 to 8 ft
early next week.

McMillian

&&

.HYDROLOGY...The daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Thursday for Central U.S.
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 5 PM this afternoon to 5 AM PDT
     Thursday for East Entrance U.S. Waters Strait Of Juan De
     Fuca-Northern Inland Waters Including The San Juan Islands.

&&

$$