Small Craft Advisory 99, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
848 PM PDT Wed May 9 2018

.SYNOPSIS...An upper trough will bring cooler showery weather to
the region through Thursday. An upper ridge will build over Western
Washington beginning Friday, giving dry weather and a warming
trend through Sunday. Onshore flow will return around Monday,
moderating temperatures somewhat early next week.

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.SHORT TERM...An upper trough offshore will move to the coast
Thursday morning. There are some showers ahead of the trough this
evening - mostly over the Cascades and the San Juans. This shower
activity should decrease tonight with the loss of daytime heating.
However, showers will increase again and become more widespread
Thursday morning as the upper trough moves overhead. The upper
trough will push east of the area Thursday afternoon and evening.
There should be a corresponding decease in showers across the
area. A Puget Sound Convergence Zone is possible later Thursday
although there isn't a strong signal in the models. The showers
and additional cloud cover should cool highs back to near or even
slightly below normal on Thursday.

An upper ridge will build into the area from the west Friday and
Saturday for a drying and warming trend. A few showers might
linger into Friday over the Cascades. Otherwise it should be dry
with morning clouds and afternoon sunshine. Low level onshore flow
will continue but not as strong as on Thursday. Highs will warm
around 5 degrees with 60s for most areas. Low level onshore flow
will weaken and turn more northerly on Saturday and the upper
ridge will strengthen over the area. This should give a sunny day
with highs warming into the 70s for most areas. Schneider

.LONG TERM...Previous discussion...Sunday looks like the warmest
day, with the highest 500 mb heights and fairly well developed
northerly and offshore surface flow. Highs will be in the 70s and
80s, with mid 80s in the southwest interior. After that the
weather will remain dry, but the surface flow will turn onshore. A
two-day marine push looks likely, with highs falling to near 80
on Monday and into the 70s Tuesday, except on the coast where each
day will have highs in the 60s. Each day next week will probably
have morning clouds and afternoon sun. Wednesday will be a few
degrees cooler still. Burke

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.AVIATION...An upper trough will move to the coast Thursday
morning and inland later Thursday with southwest flow aloft
becoming northwest. At the surface, moderate onshore flow this
evening will ease after midnight. A weak surface trough will move
onshore Thursday morning. Strong onshore flow will develop behind
the trough later Thursday. The air mass is moist and slightly
unstable.

Mostly VFR mid and high clouds this evening. Low and mid level
moisture will increase after midnight tonight as the upper trough
reaches the area. MVFR low clouds are expected most areas
Thursday morning. Ceilings should improve Thursday afternoon.

KSEA...Scattered clouds this evening. Mid and high clouds
increasing after midnight. MVFR low clouds expected Thursday
morning with ceilings lifting to VFR in the afternoon. Southerly
wind 6-12 knots. Schneider

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.MARINE...Moderate onshore flow will produce small craft advisory
strength west winds in the Central and Eastern Strait of Juan de
Fuca tonight. A trough will shift through the area early Thursday.
Onshore flow will become strong behind this trough later
Thursday. Gale force west winds are expected for the Central and
Eastern Strait late Thursday. Small craft advisory strength
westerly winds are possible for most other waters Thursday night.

Moderate onshore flow will continue into Friday with small craft
advisory strength west winds for the Coastal Waters and Strait.
Onshore flow will weaken over the weekend and then strengthen
again early next week. Schneider

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.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Thursday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Gale Warning from 3 PM Thursday to 3 AM PDT Friday for Central
     U.S. Waters Strait Of Juan De Fuca-East Entrance U.S.
     Waters Strait Of Juan De Fuca.

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