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000
FXUS66 KSEW 250248
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
748 PM PDT Wed Apr 24 2024

.SYNOPSIS...Weakening front dissipating over Western Washington
this evening. Next system moving over Western Washington and
stalling Thursday before moving east Thursday night. Cool upper
level trough over the area Friday. Another weather system
arriving Saturday. Upper level trough over the area Sunday into
the middle of next week keeping temperatures below normal into
the first part of May.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY/...
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No changes were made to
the forecast this evening. The previous discussion can be found
below along with updated aviation and marine sections:

Front will continue to move slowly east eventually dissipating
over the Cascades later this evening. Not much rain left with the
front with less than a tenth of an inch possible. A little break
behind the front late tonight into early Thursday morning with the
next system currently just east of 140W. Cloudy skies overnight
will keep lows in the mid to upper 40s.

Rain ahead of the next system moving into Western Washington
Thursday morning. Weak jet associated with the front digging
south into Oregon Thursday afternoon. This will cause the front
to stretch out, weaken and become stationary over Western
Washington making for a wet late April day. Rain most of the day
will make for little in the way of daytime heating with the high
temperatures only a few degrees above the lows, in the lower to
mid 50s.

As the jet continues to dig south front dissipating over Western
Washington late Thursday night into Friday morning. Daily rainfall
records are on the low side Thursday. For example, the record
rainfall for Seattle is 0.59 inches set in 2020. There is a chance
some daily rainfall records could be broken, not so much from
heavy rain just steady rain all day Thursday. Seattle April
monthly rain total currently at 0.43 inches so there is a chance
Seattle gets more rain Thursday than the previous 24 days in
April. Steady rain giving way to more showery precipitation with
the front dissipating early Friday morning. Lows once again in the
mid to upper 40s.

Cool upper level trough hanging out over the area Friday. Jet well
to the south with little dynamics overhead but cooler air mass
aloft enough to keep showers in the forecast. It will be another
below normal day temperature wise with highs in the mid to upper
50s.

Upper level trough shifting east Friday night with showers coming
to an end. Next system reaching Western Washington during the day
Saturday with rain spreading back over the area. Parent low for
the front in the Northern Gulf of Alaska so this will not be a
strong system with rainfall amounts mostly under a tenth of an
inch. Lows Friday night in the 40s with highs Saturday in the mid
to upper 50s.

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...Extended models remaining
consistent in the idea of a cool upper level trough over Western
Washington Sunday and Monday. Snow levels dropping down to near
3000 feet Monday bringing up the possibility of light snow on all
the passes. Some differences in the models show up beginning
Tuesday. There is good agreement that a closed low will form in
the trough Tuesday but the location of this feature is much
different with the GFS taking the low well offshore Wednesday while
the ECMWF has the low much closer to the coast. Even with the
different locations of the upper level low both solutions keep
showers over Western Washington Tuesday and Wednesday along with a
continuation of below normal temperatures. It`s going to be a cool
last week of April for Western Washington. Felton
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&&

.AVIATION...
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Westerly flow aloft this evening becoming more
southwesterly by early Thursday morning as a weak shortwave trough
begins to work its way to the coast. Surface winds generally from
the south at 5-10 kts, however PAE remains more northerly...although
there is the expectation for winds there to shift more southeasterly
by 06Z tonight. Speeds expected to pick up starting Thursday morning
getting up to 10-15 kts sustained by early afternoon with gusts to
25 kts possible.

Generally VFR conditions over the CWA with two notable
exceptions...MVFR conditions present along the Strait and spilling
over into western Snohomish county /including PAE/ and IFR
conditions over a small area in the south Sound in and around the
Tacoma area. Persistent threat of rain and lingering low level
moisture will help to ensure that cigs will lower throughout the
night with widespread MVFR conditions in place for most terminals by
10Z while PAE, PWT and HQM may see conditions erode further with IFR
conditions expected by early morning. While cigs might get a slight
nudge upward by Thursday afternoon, widespread MVFR to IFR
conditions are expected to persist for the remainder of the TAF
period.

KSEA...Low end VFR to occasional MVFR should persist through early
evening. Solidly MVFR conditions after 06Z with rain coming in after
12Z. Limited visibility possible in brief periods of increased
rainfall. SW winds 4-8 kt tonight before increasing to S 8-12 kt
with gusts up to 20kt possible tomorrow.

18/LH
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&&

.MARINE...
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Scattered showers continue across the coastal waters in
the wake of dissipating front. A more substantial system will move
through the area waters on Thursday. Southerly winds will increase
throughout the coastal waters, but the areas with the best chance to
see Small Craft Advisory conditions will be in waters south of Point
Grenville (50-85% probability, especially within 20 NM of shore). As
such, a Small Craft Advisory remains in effect for Thursday there.
Additionally, rain will be heavy at times, which will likely reduce
visibilities as low as 1-3NM during the heaviest rain.

Breezy conditions will continue on Friday for the outermost coastal
waters as the low pressure center moves through western Washington.
A weak surface ridge will calm things down on Saturday before another
front moves through the region Sunday. The active pattern looks to
continue into the beginning of next week.

Seas look to remain 4 to 6 feet at about 10 seconds through the rest
of the week and into Saturday. Seas look to rise to 8 to 10 ft
beginning Sunday.

LH/18
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&&

.HYDROLOGY...No river flooding expected in the next 7 days.
Heavier rain over the south slopes of the Olympics Thursday into Thursday
night could push the Skokomish River in Mason county close to
action stage Friday. Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 5 AM to 5 PM PDT Thursday for Coastal
     Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-
     Coastal Waters From Point Grenville To Cape Shoalwater Out
     10 Nm.

&&

$$