Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 241001

Area Forecast Discussion
National Weather Service Seattle WA
300 AM PDT Tue Apr 24 2018

.SYNOPSIS...Upper level ridging over Washington will keep conditions
dry through Thursday. Warm temperatures are also expected with many
locations seeing afternoon highs in the 70s. An upper level low will
approach from the southwest late in the week bringing a return to
seasonably cool temperatures and a chance of showers Friday and
into next weekend.


.SHORT TERM...A bit of a spread in temperatures this early morning
across W WA...with the southern half of the CWA seeing temps in the
50s while the northern half is stuck in the 40s...all under some
scattered high clouds.

The upper level ridge responsible for this stretch of dry conditions
looks to remain in place today before gradually moving southeastward
Wednesday. Not much of a change in the weather an upper
low plunging into western Montana will actually put W WA under the
influence of a secondary ridge...allowing dry and warm conditions to
persist into at least Thursday afternoon. Looking at surface
features...a surface high over the area will allow for offshore
flow...helping to push temps up a degree or two each day. Warmest
day of the week looks to be Thursday...with the potential for some
locations to crack 80 degrees.

Locally breezy to windy conditions still a possibility over the
Cascade foothills this morning. Pressure gradients continue to
gradually relax...but the prospect for wind gusts up to 30 to 40 mph
will still be in play through the morning hours.
other significant wind issues expected for the area.

All in all...about as quiet a short term forecast as one could hope
for.  SMR

.LONG TERM...A change over to onshore flow starting as early as
Thursday evening will start to signal a change in the pattern. An
upper level low over the Pacific making its way toward southern
OR/northern CA will push up showers from the southwest up into W WA
late Friday morning/early Friday afternoon. While models do not
particularly agree on the details of this low...its movement/track
or the presence of any secondary systems that may either follow it
(ECMWF) or fold into it (GFS)...the broad strokes end up lining up
with showery weather expected for much of the upcoming weekend and
temperatures cooling to more seasonal values with afternoon highs in
lowland locations during this time frame only reaching the mid 50s.


.AVIATION...An upper ridge axis is centered along the Cascades this
morning with light southerly flow aloft over Western Washington. The
air mass is dry and stable with little more than some thin high
level moisture crossing the region. At the surface, low level
offshore flow will continue today as a ridge remains anchored east
of the Cascades with thermally-induced low pressure along the coast.

KSEA...VFR through the day and tonight with just some high clouds at
times. Low level offshore flow continues today. The cross-Cascade
gradient should peak 12Z-15Z. East-Northeast wind 6 to 10 knots
through early this morning becoming northerly 7 to 12 knots from mid
morning through the evening.      27


.MARINE...High pressure inland and thermally induced low pressure
along the Oregon and Washington coast will persist until about
Thursday morning. This pattern leads to northerly offshore flow.
Small craft advisory strength easterlies are forecast this morning
and again on Wednesday morning in the vicinity of Cape Flattery.
The thermally induced low pressure will move inland on Thursday
with onshore flow developing Thursday night and Friday. Westerly
flow through the Strait should peak on Friday night. Haner


PZ...Small Craft Advisory until 1 PM PDT this afternoon for Coastal
     Waters From Cape Flattery To James Island Out 10 Nm-West
     Entrance U.S. Waters Strait Of Juan De Fuca.


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