Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 122329

Area Forecast Discussion
National Weather Service Seattle WA
429 PM PDT Thu Apr 12 2018

.SYNOPSIS...A strong low pressure system will bring a round of wet
and locally windy conditions to the region Friday and Friday
night. Expect the cold front to very slowly move southeast across
parts of the area on Saturday. Cool and unsettled conditions are
expected Saturday night through Sunday under low pressure aloft.


There were scattered showers over the CWA at this time. Overall,
the activity has been decreasing.

Expect the next Pacific storm to begin impacting the region late
tonight. A warm front will slowly move across the the western
part of the CWA Friday morning before hanging up between the
Olympic range and Cascades. Expect the heaviest precipitation to
occur on the coast and in the mountains on Friday. The Winter
Storm Watch for the Cascades in Pierce and Lewis Counties was
upgraded to a Winter Storm Warning. About 1-2 feet is likely above
the 4500 foot level by Saturday morning. A Winter Weather Advisory
was also issued for the Cascades in Whatcom and Skagit Counties
above the 4000 foot level for 10-18 inches of snow during the
same time frame. Will need to keep an eye on the north Cascades
because the forecast snowfall amounts are borderline warning

The surface pressure gradient will also tighten during the day
Friday for locally windy conditions, especially over parts of the
coast and northwest interior.

Look for a cold front to slowly move southeast across the CWA
Friday night for locally heavy precipitation and locally windy
conditions. The focus of the heaviest precipitation will shift
into the Cascades and southwest interior by daybreak Saturday.
Total rainfall amounts of 1-3 inches are forecast for the Cascades
and coast and 3-5 inches on the Olympic range during the 24-hour
period ending 5 AM PDT, Saturday. This amount of rain will cause
some rivers to rise.

The cold front will creep southeast across the southeast part of
the CWA during the day Saturday. The precip will become more
spotty northwest of the front Saturday afternoon. Overall, the
precipitation intensity should decrease during the day. There is a
chance that the Winter Storm Warning may need to be extended
through daytime Saturday for the Cascades in Pierce and Lewis

An upper level low will slowly approach the region Saturday night
and Sunday for cool and showery conditions.

An upper level trough will prevail over the region on Monday for
continued unsettled weather and below normal temps. A weak and
dirty ridge will move over the region on Tuesday. The upper level
flow will become weakly split about the middle of next week,
resulting in gradually improving conditions for the CWA. It looks
like Thursday will be a dry day under high pressure aloft. Alas,
the ridge will weaken the end of the period, allowing an upper
level trof to approach from the west.


.AVIATION...A trough will move inland this evening. A frontal
system will move slowly through the area Friday and Friday night.
Moist unstable air this evening will become stable Friday. Westerly
flow aloft. Scattered showers will switch back to rain around
daybreak Friday. Mountains obscured.

KSEA...A few showers this evening and then another frontal system
arrives by daybreak Friday with more rain.


.MARINE...A vigorous frontal system will give southerly winds 20-30
knots to the coastal waters and most of the inland waters on Friday.
Small craft advisories will be up for most of the area Friday and
there is a chance that it will reach gale in a few of the normally
windier spots. The front will move inland around daybreak Saturday
with much lighter winds.


Additional heavy rainfall Friday and Friday night will probably
cause the Skokomish River to rise above flood stage (16.5 feet)
early Saturday. The river is forecast to crest near 17.5 feet
Saturday afternoon before falling below flood stage Sunday
afternoon. Elsewhere, expect rises on some rivers this weekend;
otherwise flooding is not anticipated the next 7 days.


WA...Winter Storm Warning from 5 AM Friday to 6 AM PDT Saturday for
     Cascades of Pierce and Lewis Counties above 4500 feet.

     Flood Watch from Friday evening through Saturday afternoon for
 the Skokomish River in Mason County.

     Winter Weather Advisory from 6 AM Friday to 6 AM PDT Saturday
     for Cascades of Whatcom and Skagit Counties above 4000 feet.

PZ...Small Craft Advisory for rough bar until 5 PM PDT Friday for
     Grays Harbor Bar.

     Small Craft Advisory until 5 PM PDT Friday 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 3 AM to 5 PM PDT Friday for Admiralty
     Inlet-East Entrance U.S. Waters Strait Of Juan De Fuca-
     Northern Inland Waters Including The San Juan Islands.

     Small Craft Advisory for hazardous seas until 5 AM PDT Friday
     for West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 3 AM to 11 PM PDT Friday for Puget
     Sound and Hood Canal.


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