491
FXUS66 KSEW 301011
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
311 AM PDT Tue Apr 30 2024

.SYNOPSIS...Shower activity will continue through the evening
tonight before shifting southward. Conditions will be drier and
warmer Wednesday through Friday, with cooler and wetter weather
returning by the weekend.

&&

.SHORT TERM /TODAY THROUGH THURSDAY/...A surface low will continue
to push onshore through the morning and slide eastward throughout
the day as an upper trough axis shifts over the Pacific Northwest.
Scattered showers will continue to stream eastward through the
morning hours, slowly shifting southward through the afternoon as
high pressure builds inland behind. The core of the surface low
will track onshore along the Columbia Gorge today, enhancing
instability with ensembles showing an average of 200-300 J/kg this
afternoon mainly south and west of Seattle. Lightning and graupel
cannot be ruled out of any stronger showers that develop in the
afternoon. Precipitation will taper off by the evening, with
temperatures staying on the cool side peaking in the mid 50s
across the lowlands.

Weak ridging will allow conditions to dry out late Tuesday, and
decreasing cloud cover overnight into Wednesday morning will allow
some locations to see temperatures bottom out near freezing.
Otherwise, dry conditions will prevail for much of the day
Wednesday with highs warming up to the upper 50s and lower 60s.

Another weak low pressure system will pass over the region late
Wednesday into Thursday, with some uncertainty remaining over the
exact track of the storm system. While most models bring this
system south of the area, a chance of precipitation is maintained
for much of the area through Thursday, favoring higher terrain.
Snow levels will hover near 3500-4000 ft with light precipitation
amounts, and temperatures will continue a warming trend increasing
into the low to mid 60s.

.LONG TERM /FRIDAY THROUGH MONDAY/...Weak ridging will expand
inland late Tuesday through Friday morning, with the potential for
some areas to approach 70 degrees by Friday afternoon. A low
pressure system is on track to move towards the Pacific Northwest
by next weekend, but forecast models show fairly large differences
in terms of placement and timing of any precipitation with this
system. While uncertainty remains through the weekend, ensembles
favor a cooler and wetter troughing pattern through Monday with a
return to near-normal or slightly cooler temperatures.

Lindeman

&&

.AVIATION...Westerly flow aloft will become more northerly as an
upper level low moves inland today. At the surface, a weak low
offshore will gradually make its way inland towards the WA/OR
border late this morning into early this afternoon. Radar shows
scattered shower activity across the area this morning, with the
heaviest showers currently moving inland along the coast. Current
conditions are a mix of VFR and MVFR across the area terminals
this morning, but expect conditions to become more widespread MVFR
through the early morning hours. MVFR ceilings then look to lift
back to widespread VFR by this afternoon. Isolated thunderstorms
will be possible at times for terminals mainly along the coast and
from the central Sound southward, though confidence is too low at
this time to include in TAFs. Showers will gradually taper across
the region this afternoon and evening. Low level winds persist
primarily out of the south at 3-7 kt this morning, but look to
shift to the north late morning and increase to 5-10 kt at times.
Winds then look to ease back to 3-7 kt by this evening.

KSEA...Current conditions VFR with southerly winds persisting
generally at 3-7 kt. Expect conditions to become MVFR this morning
and to persist through 18Z, before lifting back to VFR this
afternoon. Additional shower activity is likely at the terminal
today. Isolated thunder cannot be ruled out, though confidence is
low at this time. Winds look to shift to the north between 18-20Z
and persist at 5-10 kt through the evening hours before easing
back to 3-7 kt between 03-06Z Weds. 14

&&

.MARINE...A few small craft gusts continue across portions of the
Eastern Strait early this morning, but expect the wind to ease
over the next few hours. A weak surface low will traverse the
coastal waters today and push inland along the WA/OR border by
late morning/early afternoon. Seas look to briefly build towards
10 feet over the outer coastal waters this morning, so have issued
a small craft for these zones through this afternoon. May see
another low-end advisory strength push of westerly winds through
the Strait tonight into early Wednesday, with probabilities
highlighting a 50-60 percent chance of gusts occasionally
exceeding 21 kt. Have held off of small craft issuance for now,
however this will continue to be monitored through the day.

High pressure will then build back into the area waters tonight
into Wednesday, before yet another low and its associated frontal
system move into the region Wednesday night into Thursday. The
period will remain active, with another frontal system expected to
traverse the area waters Friday night into the weekend.

Seas over the outer coastal waters look to subside below 10 ft
tonight. Seas over all the coastal waters will continue to subside
into midweek, hovering between 3 to 6 ft Wednesday through
Friday. Seas will then increase closer to 6 to 8 ft again over
the weekend. 14

&&

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

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 PM PDT this afternoon for Coastal
     Waters From Cape Flattery To James Island 10 To 60 Nm-
     Coastal Waters From James Island To Point Grenville 10 To
     60 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater 10 To 60 Nm.

&&

$$