783
FXUS66 KSEW 302143
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
243 PM PDT Tue Apr 30 2024

.SYNOPSIS...Shower activity will taper off overnight with
unusually cool temperatures and areas of frost by Wednesday
morning. Another weak system will slide to our south on late
Wednesday into early Thursday. Drier and slightly warmer
conditions are expected Thursday and Friday before more
precipitation arrives late Friday and Saturday.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...A low pressure system
continues to progress east near Portland this afternoon. Isolated
to scattered showers continue to wrap around this system and will
gradually taper off through this evening. A stray thunderstorm or
two still cannot be ruled out this afternoon, with the highest
chances closer to Portland. Clearing skies and a cooler airmass
will result in areas with temperatures reaching into the low to
mid 30s tonight allowing for areas of frost development. A Frost
Advisory remains in effect for tonight.

A weak system will slide mainly south of the area late Wednesday
into early Thursday bringing another window of possible shower
activity, mainly south and west of Seattle. This will be followed
by transient ridging Thursday into early Friday allowing
temperatures to warm into the 60s Thursday and Friday. The next
system will begin to spread precipitation across the area Friday
afternoon and evening.

.LONG TERM /SATURDAY THROUGH TUESDAY/...A broad upper level low
will make its way to the coast Friday night. Cluster analysis
continues to indicate disagreement in the evolution of this low.
Roughly half of the members take the bulk of the low and
associated precipitation to the south while the other half keep a
more progressive pattern moving the system across Washington
fairly quickly but with heavier rainfall. In either case, the
system will be associated with at least some precipitation and wet
conditions are likely late Friday through Saturday.

Beyond the early weekend system, zonal flow and at least semi-
active weather is expected to continue. This will keep
temperatures in check and a chance of precipitation in the
forecast.
-Wolcott-

&&

.AVIATION...Cool upper level trough shifting east tonight into
Wednesday. Light flow aloft becoming northerly overnight. In the
lower levels northerly flow this evening turning back to onshore
overnight into Wednesday morning.

VFR ceilings over most of the area with MVFR ceilings with
scattered showers until 04z. Skies clearing from north to south
after 04z with increasing middle level clouds after 15z Wednesday
morning. Patchy visibility 1 sm or less Northwest and Southwest
Interior 12z-16z.

KSEA...MVFR ceilings lifting to VFR 21z-23z. Skies clearing after
05z. Light southerly winds switching to northerly 18z. Northerly
winds 8 to 10 knots 22z-04z. Winds switching back to southwesterly
6 knots or less after 06z. Felton

KSEA...Ceilings near 4000 feet this evening with skies clearing
overnight. Increasing middle level clouds after 14z with ceilings
aoa 6000 feet. Northwest wind 6 to 9 knots becoming southerly 6
knots or less after 06z. Felton

&&

.MARINE...Low level flow becoming onshore tonight with surface
high pressure building over the coastal waters. System moving
southeast through the coastal waters Wednesday night moving into
Northern Oregon early Thursday morning. Weak high pressure over
the waters Thursday night into Friday. Next system splitting as it
moves into the waters Friday night into Saturday. Another system
arriving late in the weekend.

Small craft advisory westerlies in the Central and Eastern Strait
late tonight into early Wednesday morning.

Seas near 10 feet tonight subsiding to 6 or 7 feet early Wednesday
morning. Felton

&&

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

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Frost Advisory from 8 PM this evening to 10 AM PDT Wednesday for
     East Puget Sound Lowlands-Everett and Vicinity-Hood Canal
     Area-Lower Chehalis Valley Area-Southwest Interior-Tacoma
     Area.

PZ...Small Craft Advisory from 11 PM this evening to 5 AM PDT
     Wednesday for Central U.S. Waters Strait Of Juan De Fuca-
     East Entrance U.S. Waters Strait Of Juan De Fuca.

&&

$$