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fxus66 ksew 202225 
afdsew

Area forecast discussion
National Weather Service Seattle Washington
330 PM PDT Fri Oct 20 2017

Synopsis...showers will continue over the area through tonight with
some mountain snow. A strong storm system will affect the region
over the weekend. Rain will increase Saturday and become heavy at
times, especially over the coast and mountains. There may be snow
accumulation in the Cascades Saturday before snow levels rise. Drier
weather will develop Monday and Tuesday.

&&

Short term...in a generally showery pattern, a convergence zone
appears to be forming in Snohomish County. This is forecast to move
into the Cascades this evening and produce snow in advisory amounts--
six to eleven inches--in the central Cascades down to 3500 feet or
so, which includes Stevens Pass. There is likely to be a few inches
of new snow in other Cascade zones tonight.

A warm front will bring rain to the coast late tonight; the rain
will spread into the interior Saturday morning. The heaviest rain
with the warm front will first reach western Oregon, then move north
over western Washington Saturday afternoon and evening. A cold front
will reach the area Sunday morning and rain will turn to showers.
Rainfall amounts are currently forecast to be 2-4 inches in the
north Cascades and Olympics, and 4-6 inches in the central and south
Cascades, with some higher bullseyes. The Lowlands will get an inch
or so in the north and two inches or more in the south. Flooding is
likely on area rivers; most flooding will be on Sunday and could
last into Sunday night.

Showers will taper considerably Sunday night and will likely be
completely over on Monday. Skies will start to clear on Monday. High
temperatures will be 55-60 Saturday, near 60 Sunday, and in the low
60s Monday. Burke

Long term...Tuesday continues to look like a sunny and warm day.
Heights will be near 590dm. Highs are currently forecast to be in
the 60s and could go higher. A weak weather system will move through
the region Wednesday, giving a chance of showers. After that, dry
northerly flow sets up, with sunny skies and highs 55-60 on both
Thursday and Friday. Burke

&&

Hydrology...new quantitative precipitation forecast from a blend of most recent mesoscale model
runs boosted river crests a bit in the river model. The river model
has rivers from the Skykomish south reaching minor to moderate flood
levels. The Skokomish River in the Olympics also seems more likely
to flood with the new quantitative precipitation forecast. The Skykomish, Snohomish, Snoqualmie,
Carbon, and Cowlitz rivers are the rivers most likely to crest above
the moderate flood level. In general, flooding will occur on Sunday
from heavy rain Saturday night. The Flood Watch remains in effect
for all of western Washington.

The burn scar from the recent Norse Peak fire presents a special
concern. Increased runoff is probably in the burn area and there is
some chance of debris flows. The goat creek valley and the Crystal
Mountain ski area are at risk of flash flooding, which could reach
all the way to State Route 410. A Flash Flood Watch is in effect for
this small area.

Despite recent heavy rains, there has not been enough accumulated
precipitation to saturate soils. Even after the forecast rain this
weekend, the general threat of landslides and mudslides will not be
significantly raised above the normal level. Burke

&&

Aviation...westerly flow aloft continues over western Washington
this afternoon as an upper trough moves slowly across the Pacific
northwest. Westerly flow aloft will increase tonight and Saturday as
a vigorous Pacific frontal system moves into the region. The air
mass will remain moist through saturday; it will be weakly unstable
this evening and then become stable.

Cloud cover this afternoon is roughly scattered-bkn023 broken-ovc045 with
additional layers to around 10,000 feet. Scattered showers continue
across the area, bringing locally lower conditions.
Showers will probably decrease this evening with marginal
improvement, except in the Puget Sound convergence zone north of
Seattle. Conditions will lower later tonight as warm frontal rain
spreads into western Washington. Low-end MVFR and local IFR
conditions will probably prevail most of the day Saturday.

Ksea...southwest wind 10-15 kt for the next few hours, becoming
south to southeast 8-12 kt, rising to 13-20 kt gusting 30 kt late
Saturday afternoon or Saturday evening. Some improvement to VFR
conditions is likely this evening. There will probably be a weak
Puget Sound convergence zone, north of sea and bfi.
Conditions will deteriorate again tonight, and low-end MVFR
conditions due to ceilings and visibility in rain should prevail
most of the day Saturday. South wind 7-13 knots. Mcdonnal

&&

Marine...onshore flow this evening will turn easterly tonight
ahead of an approaching warm front. Small Craft Advisory winds will
continue this evening over most of the waters; the strongest winds
will likely be the westerlies in the central and eastern Strait of
Juan de Fuca.

A vigorous Pacific frontal system will move through the area
Saturday and Saturday night, with gale force southeast winds over
the coastal waters, East Entrance Strait of Juan de Fuca, and
northern inland waters. Small Craft Advisory winds are expected over
the remaining waters. There could be another period of gales over
the south part of the coastal waters Saturday evening.

Onshore flow behind the frontal system will ease and eventually turn
weakly offshore later Monday and continue Tuesday. A weak system
will move through the area on Wednesday. Mcdonnal

&&

Sew watches/warnings/advisories...
Washington...Flood Watch from Saturday afternoon through late Sunday night
for Admiralty Inlet area-Bellevue and vicinity-Bremerton
and vicinity-Cascades of Pierce and Lewis counties-Cascades
of Snohomish and King counties-Cascades of Whatcom and
Skagit counties-central coast-east Puget Sound lowlands-
eastern Strait of Juan de Fuca-Everett and vicinity-Hood
Canal area-lower Chehalis valley area-north coast-Olympics-
Seattle and vicinity-southwest interior-Tacoma area-western
Skagit County-western Strait of Juan de Fuca-western
Whatcom County.

Winter Weather Advisory until midnight PDT tonight for Cascades
of Snohomish and King counties.

Pz...Small Craft Advisory for rough bar until 6 PM PDT Saturday for
Grays Harbor bar.

Small Craft Advisory until 2 am PDT Saturday 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.

Gale Warning from 2 am to noon PDT Saturday 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 until 3 am PDT Saturday for East Entrance
U.S. Waters Strait of Juan de Fuca.

Gale Warning from 3 am to 3 PM PDT Saturday for East Entrance
U.S. Waters Strait of Juan de Fuca-northern inland waters
including the San Juan Islands.

Small Craft Advisory until midnight PDT tonight for Admiralty
Inlet-central U.S. Waters Strait of Juan de Fuca-northern
inland waters including the San Juan Islands-Puget Sound
and Hood Canal.

Small Craft Advisory until 6 PM PDT Saturday for West Entrance
U.S. Waters Strait of Juan de Fuca.

&&

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