Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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265
FXUS66 KSEW 162155
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
255 PM PDT Mon Apr 16 2018

.SYNOPSIS...Weak upper features combined with moist onshore low
level flow will result in scattered showers Tuesday and isolated
showers on Wednesday. An upper ridge will bring dry weather
Thursday into Friday. The next frontal system will move through
quickly on Saturday, with dry weather likely on Sunday and Monday.

&&

.SHORT TERM...An upper low will exit the area tonight. Showers
will taper and become somewhat confined to the mountains and a
Puget Sound Convergence Zone by Tuesday morning. Snow in the
mountains should ease by Tuesday morning as well. Stevens Pass
may get an extra shot tonight in the convergence zone however.
Paradise on Mount Rainier has already picked up a foot today and
should get several more inches this evening. Moderate low level
onshore flow will bring breezy to locally windy conditions tonight
and Tuesday.

There will be enough lingering instability that showers will
become likely again in spots Tuesday afternoon. A few showers
will linger into Wednesday with a weak upper trough over the area
but the trend will be for drying. Dry weather and more sunshine
is expected for Thursday as an upper ridge builds over the area.
Highs will creep up over the next few days and be back to near
normal by Thursday. Schneider

.LONG TERM...High pressure aloft will produce a dry day Friday
although rain from an approaching front may reach the western part
of the area late in the day. The aforementioned front will move
onshore Friday night and Saturday with rain changing to showers.
High pressure aloft will return Sunday and Monday for dry weather.
Highs will warm into the 60s. Schneider

&&

.AVIATION...An upper level and surface low over northwestern
Washington will lift northeastward into southeastern British
Columbia tonight and well east of the area on Tuesday. Strong
west to northwest flow aloft through Tuesday. The air mass is
moist and weakly unstable below about 10000 feet and stable
above.

Radar and satellite imagery continues to show bands of clouds and
moisture rotating around the upper low over the area this
afternoon and most terminals are seeing MVFR conditions. Expect
showers to become increasingly confined to the mountains and a
central Puget Sound Convergence Zone tonight through Tuesday as
the low moves away from the area and flow aloft interacts with the
coastal terrain. Conditions will improve to mainly VFR Tuesday
morning as breaks on either side of the convergence zone grow in
size. Albrecht

KSEA...Another rain band is impacting the terminal early this
afternoon and it appears that it will persist into this evening.
Southerly flow appears that it will be strong enough to keep
convergence zone activity later tonight and Tuesday north of the
terminal. Expect mainly MVFR conditions through tonight with VFR
conditions developing around 15Z Tuesday. Winds will persist from
the SSW at 15ktG25-30 kt through tonight then slowly tapering off
on Tuesday. Albrecht

&&

.MARINE...Low pressure over the inland waters this afternoon will
lift northeastward into southeastern portions of British Columbia
tonight then well east of the area on Tuesday. Strong onshore flow
is wrapping around the south side of the low this afternoon. Winds
will slowly taper off on Tuesday as high pressure builds into the
area. Gale warnings remain in effect for the coastal waters and
eastern two-thirds of the Strait of Juan de Fuca; small craft
advisories are in effect for the remaining waters.

Onshore flow will gradually diminish on Tuesday and will become
light later Tuesday night through Thursday as a high builds over
the inland waters then tracks slowly northeast.

Southerly flow will increase on Friday as a cold front approaches
the waters from the west. The front will move across the region on
Saturday. Albrecht

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Storm Warning until midnight PDT tonight for Cascades of
     Pierce and Lewis Counties.

     Winter Weather Advisory until 5 AM PDT Tuesday for Cascades of
     Snohomish and King Counties-Cascades of Whatcom and Skagit
     Counties.

PZ...Gale Warning until 2 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-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 for rough bar until 3 PM PDT Tuesday for
     Grays Harbor Bar.

     Gale Warning from 6 PM this evening to 7 AM PDT Tuesday for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 6 PM this evening to 3 PM PDT Tuesday
     for Northern Inland Waters Including The San Juan Islands.

     Small Craft Advisory from 6 PM this evening to 11 AM PDT Tuesday
     for West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 8 PM this evening to 11 AM PDT Tuesday
     for Admiralty Inlet.

     Small Craft Advisory until 11 AM PDT Tuesday for Puget Sound and
     Hood Canal.

&&

$$

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