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181
FXUS66 KSEW 061021
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
321 AM PDT Mon May 6 2024

.SYNOPSIS...
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Cool and showery conditions continue across the region
through Tuesday with lowland rain and mountain snow expected.
Expect a Puget Sound Convergence Zone to develop later today and
isolated thunderstorms remain possible across the area. A shift in
the pattern will develop toward midweek, bringing dry conditions
and steadily warming temperatures through the second half of the
week.
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.SHORT TERM /TODAY THROUGH WEDNESDAY/...
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An approaching front is
nearing the coastline early this morning, with widespread low
clouds and breezy winds across most of western Washington. Expect
a rather cloudy and somewhat wet start to the day across the
region as the front sweeps across this morning, followed by the
trailing upper trough that moves eastward through the day. Behind
the front, expect to see widespread showers and isolated
thunderstorms across the area. With these thunderstorms and strong
showers, the most likely hazard beyond lightning is small hail.

Meanwhile, snow levels will drop and some light snow is possible
down to around Stevens Pass and possibly closer to Snoqualmie Pass
by the evening. While general amounts look to be rather limited,
a developing Puget Sound Convergence Zone will bring the focus for
additional heavier precipitation into the late afternoon and
evening hours. Best chances for accumulating snow will be up in
the higher mountain elevations with temperatures near the surface
limiting the potential for impactful accumulations outside of
under heavier rates under a PSCZ if it drifts into the Cascades.
There`s around a 20-30% chance of 3" at Snoqualmie Pass late
Monday through early Tuesday morning, but amounts most likely
remain around an inch at most. Chances are similar for Stevens
Pass.

Temperatures will remain quite cool with afternoon highs only
topping out in the lower to mid 50s through the interior lowlands,
which is around ten degrees below seasonal normals. Some
lingering showers into Tuesday, but these will become increasingly
confined to the mountains as the upper trough slides east and the
orographic flow becomes increasingly necessary to maintain
activity.

The shift in the pattern begins to become more pronounced
Wednesday with ensemble guidance remaining in strong agreement
that an upper ridge will amplify and take up residence over the
western U.S. Expect cloud cover to gradually decrease and
temperatures to begin to warm into the lower 60s for much of the
region. A more significant warm up will follow late in the week.

.LONG TERM /THURSDAY THROUGH SUNDAY/...Ensemble guidance
continues to depict high confidence in a much warmer pattern
across the Pacific Northwest late in the week as an upper level
ridge builds over the region. Still some variations evident in
the clusters of ensemble members with respect to where the ridge
axis sets up and just how strong it is, but confidence is high in
seeing temperatures climb to at least 10 to 15 degrees above
normal by the late stages of the week for much of the lowlands.
Current forecast from the NBM suggest a run into the lower to mid
80s for the warmest spots Saturday with Friday and Sunday only a
few degrees cooler for most. While the precise temperature
forecast will fluctuate a bit in the coming days, it`s worth
noting that this will be a significant warm up and coupled with
the calendar turning to May, many folks may be out around area
water. Keep in mind that local waters are still quite cool and be
sure to adhere to safety practices if you`re out in or around the
water later this week. Cullen
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.AVIATION...
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Cool upper level trough moving into the area this
morning and remaining over Western Washington into Tuesday morning.
Southwesterly flow aloft becoming northwesterly this afternoon. At
the surface, front along the coast moving through the interior
this morning. Increasing onshore flow behind the front later this
morning through this afternoon. Convergence zone developing north
of KPAE this morning slowly moving south reaching KSEA 06z-09z
tonight.

Ceilings mostly MVFR early this morning with isolated IFR
ceilings along the coast and over the Kitsap peninsula. Ceilings
improving to VFR most locations outside of the convergence zone
later this morning into this afternoon. Low end MVFR ceilings with
the convergence zone through tonight. Air mass destabilizing
behind the front with MVFR ceilings also possible with isolated
thunderstorms late morning through early evening.

KSEA...MVFR ceilings improving to VFR later this morning. Ceilings
lowering back down to MVFR 03z-09z with convergence zone in the
vicinity. Chance of thunderstorm 19z-06z less than 15 percent so
will leave out of TAF. Southwest wind 8 to 12 knots with gusts to
20 knots though 21z. Winds becoming variable 4 to 8 knots around
06z with convergence zone. Felton
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.MARINE...
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A frontal system will move across the waters early
this morning. High pressure building back over the area tonight
and Tuesday with the ridge remaining in place Wednesday into
Thursday. A thermally induced surface trough will build northward
along the coast later Thursday into Friday.

Small craft advisories remain up for the Puget Sound and Hood
Canal as well as for the Central and Eastern Strait of Juan de
Fuca today. Small craft advisory winds will continue in the
Central and Eastern Strait tonight with small craft winds in
Admiralty Inlet as well.

Small craft advisory winds likely for the entire Strait of Juan de
Fuca and Admiralty Inlet late afternoon and evening hours Tuesday
and Wednesday.

Seas building tonight peaking out near 10 feet Tuesday and Tuesday
night before subsiding Wednesday. Felton
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.HYDROLOGY...No river flooding is expected through the next seven days.

&&

.CLIMATE...
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.Seattle high of 51 degrees Sunday was the third coldest
May 5th on record in 80 years at Seattle-Tacoma airport. 51 degrees
is the normal high for Seattle from February 18th to the 25th. The
record low maximum for Seattle today is 48 degrees set in 1962. The
forecast high of 54 degrees is the normal high for Seattle from
March 11th through the 17th. Felton
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.SEW WATCHES/WARNINGS/ADVISORIES...
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WA...None.
PZ...Small Craft Advisory until 5 AM PDT Tuesday for Central U.S.
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 11 AM this morning to 5 AM PDT Tuesday
     for East Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 6 PM this evening to 6 AM PDT Tuesday
     for Admiralty Inlet.

     Small Craft Advisory until 6 PM PDT this evening for Puget Sound
     and Hood Canal.
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&&

$$