000
FXUS66 KSEW 160248
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
749 PM PDT Mon Apr 15 2024

.SYNOPSIS...Upper level troughing continues to bring cooler
temperatures and showers back to western Washington through
Tuesday. Ridging will then return midweek for warmer and drier
conditions, followed by a weak frontal passage over the weekend.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...Current satellite imagery
shows W WA continues to be reside under cloud cover as a weak upper
level trough sinks south into the area. Current radar remains fairly
sparse with some scattered showers making their way onto the coast
and, perhaps most noticeably, a PSCZ over eastern portions of
Jefferson county and extending into central Snohomish. This feature
remains fairly stationary at the time of this writing /730 PM PDT/,
but echoes remain light with generally amounts of up to around a
tenth of an inch possible. With minimal impacts expected from this
system, inherited forecast looks to remain on track and see no
reason for any evening updates at this time. For additional forecast
details, please refer to the Previous Discussion section below.

18

From Previous Discussion...Zonal flow aloft this afternoon as an
upper level trough slides southeastward through British Columbia,
maintaining cooler and showery conditions for our area. Recent radar
imagery this afternoon shows a developing convergence zone around
southern Snohomish/northern King county this afternoon. This feature
will likely stick around through much of the evening for central
Puget Sound and start to dissipate late tonight. Scattered showers
do look to stay around for majority of the area, but latest guidance
really shows very spotty coverage with them. High temperatures today
look to remain noticeably cooler from previous days, topping out in
the mid 50s.

Snow levels around 3000-3500 feet look to fall to around 1500-2000
feet tonight, so a few inches of snow look to be possible in and
around the mountain passes, maybe locally heavier in and around
the convergence zone as it drifts eastward.

Weak troughing will linger into Tuesday as well as scattered
showers and cooler temperatures (mid 50s). Most showers will most
likely be confined to the mountains to due some orographic
enhancement.

Troughing will progress away from the area on Wednesday, leaving
room for an upper level ridge in the NE Pacific to shift eastward
closer to our area, bringing drier and warmer conditions into
Thursday. Temperatures will begin to warm starting on Wednesday
into the lower 60s, then into the mid 60s on Thursday.

.LONG TERM /FRIDAY THROUGH MONDAY/...From Previous
Discussion...Conditions continue to be warm and dry into Friday,
with the ridge axis looking to move over western Washington. The
exact location and intensity of the ridge continues to change, so
uncertainty lies in how warm we get, but looks like mid to upper 60s
is the best bet for Friday, with Friday looking like the warmest day
of the week.

Ensemble members continue to show a weak front that may brush the
area into Saturday, which would allow temperatures to moderate
some heading into the weekend with the possibility of some
showers around. Warmer conditions still look to remain, with temps
in the long term looking to stay in the upper 50s/lower 60s.

Mazurkiewicz

&&

.AVIATION...Generally VFR conditions in place over W WA this evening
in the post frontal environment. Westerly to northwesterly flow will
continue aloft. Latest radar shows convergence zone showers
persisting across the central Sound this afternoon along with some
scattered light shower activity along the coast. With continued
onshore flow, expect convergence zone activity to linger into
Tuesday morning. As such, lower cigs and a brief shift in wind
direction will be possible for interior terminals along the central
Sound at times within its vicinity. Outside of the CZ activity, may
see some lower MVFR cigs redevelop overnight into early Tuesday
morning - mainly for terminals along the southern Sound (KOLM).
Overall conditions then look to rebound to widespread VFR by late
Tuesday morning.

KSEA...VFR conditions with southwesterly winds 4-8 kt,, although
occasional shifts to the north will continue to be an issue as PSCZ
activity continues. Associated showers remaining to the north of the
terminal, but may sag southward overnight into early Tuesday
bringing showers in the vicinity and ceilings down to MVFR at times.
These CZ showers will taper Tuesday morning, with VFR conditions
expected by Tuesday afternoon. 14/18

&&

.MARINE...Gusty onshore flow will continue in the wake of a
frontal passage tonight, with gales expected through Admiralty
Inlet and the Central and Eastern Strait of Juan de Fuca.
Elsewhere, Small Craft Advisories remain in effect for portions
of the coastal waters and for the West Entrance of the Strait
through early Tuesday. Winds will ease Tuesday and high pressure
builds into the coastal waters and interacts with lower pressure
inland. This pattern will remain in place through much of the week
for overall calmer conditions across the area waters. The next
frontal system arrives over the weekend.

Seas over the coastal waters continue to hover between 8 and 10
feet this afternoon and will gradually lower back towards 7 to 9
feet tonight into Tuesday. Seas will continue to subside through
the week, trending below 5 feet Thursday and Friday. Seas will
then increase towards 6 to 8 feet again over the weekend. 14

&&

.HYDROLOGY...No river flooding is expected through the next seven
days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Tuesday for Coastal Waters
     From Cape Flattery To James Island 10 To 60 Nm-Coastal
     Waters From Cape Flattery To James Island Out 10 Nm-Coastal
     Waters From James Island To Point Grenville 10 To 60 Nm-
     Coastal Waters From James Island To Point Grenville Out 10
     Nm-West Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Warning until 5 AM PDT Tuesday for Central U.S. Waters
     Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of
     Juan De Fuca.

&&

$$