Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 182206

Area Forecast Discussion
National Weather Service Seattle WA
300 PM PDT Tue Apr 18 2017

.SYNOPSIS...Showers will diminish this evening, then another system
will arrive on Wednesday. An upper level trough will move through on
Thursday with a ridge of high pressure following on Friday. Weak
weather systems will arrive Saturday and Sunday, with a stronger
system possible Monday.


.SHORT TERM...There have been scattered showers this afternoon,
mainly in the Cascades and East Puget Sound Lowlands. Thunderstorms
will end and the showers will diminish this evening with the end of
daytime heating and the approach of the next front. Inland areas
will likely be dry later tonight and Wednesday morning. On the coast
rain will redevelop late tonight and continue through the day. By
Wednesday afternoon light rain is likely everywhere. Rain will
continue into the evening, then turn to scattered showers late
Wednesday night. Highs Wednesday will be near 60 inland with 50s on
the coast.

An upper level trough will move over the area on Thursday with
showers and a slight chance of thunderstorms. The slightly
cooler air mass will mean highs will remain in the 50s. On Thursday
night, a sharp ridge of high pressure will build off the coast, and
on Friday it will move right over Western Washington. Heights will
be near 570dm. This implies highs in the 60s, so used guidance with
temps at the higher end. Some spots could approach 70 degrees
Friday. Burke

.LONG TERM...Friday night will also be dry but a weak system could
bring light rain on Saturday. On Sunday an upper trough will bring a
chance of showers. Highs will be mostly in the 60s on Saturday and
mostly in the 50s on Sunday. Another weak system will arrive Monday,
with a showery pattern on Tuesday. Highs both days will be mainly in
the 50s. The GFS and Euro are in good agreement about this sequence
of events, though the Euro is stronger with the Monday system. Burke


.AVIATION...Southwest to south flow aloft will prevail tonight and
Wednesday. Weak high pressure along the coast will shift inland
tonight as a front approaches. This front will move through the
area on Wednesday. The air mass is moist and unstable.

Areas of mid level clouds this afternoon will probably scatter
this evening most areas as showers diminish and brief drying
occurs in the wake of a weak front. The next front will bring
increasing moisture late tonight and Wednesday. Mid clouds are
expected to become widespread again Wednesday with VFR low clouds
developing later in the day as rain moves onshore.

KSEA...Scattered low and mid clouds through early Wednesday morning
except for some mid level ceilings in and around showers until
early this evening. Mid clouds will increase again on Wednesday
as a front moves onshore. Southerly wind 5-10 knots. Schneider


.MARINE...There will be a relative lull tonight then a front will
arrive early Wednesday. This front is expected to bring small
craft advisory winds to the Coastal Waters and Entrances to the
Strait of Juan De Fuca Wednesday. There is a small chance winds
could rise to gale over the Coastal Waters Wednesday morning.

Onshore flow will prevail behind the front Wednesday night and
Thursday as high pressure builds in from the southwest. The high
pressure will shift inland Thursday night and Friday for a period
of offshore flow. Another front will arrive on Saturday. Schneider


PZ...Small Craft Advisory until 6 PM PDT Wednesday 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-Coastal Waters From Point Grenville To Cape Shoalwater
     10 To 60 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater Out 10 Nm.

     Small Craft Advisory from 5 AM to 9 PM PDT Wednesday for East
     Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland
     Waters Including The San Juan Islands.

     Small Craft Advisory from 1 AM to 4 PM PDT Wednesday for West
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 5 AM to 4 PM PDT Wednesday for Central
     U.S. Waters Strait Of Juan De Fuca.



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