Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 191719
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
919 AM PST Sun Nov 19 2017

.SYNOPSIS...A vigorous front will move slowly through Western
Washington this afternoon and evening. Weak high pressure will be
over the area Monday. A strong warm front will arrive Tuesday. The
middle of the week will be mild, rainy, and perhaps windy at times.

&&

.SHORT TERM...A front will shift southeast through Western
Washington this afternoon and evening then stalling over southwest
Washington and Western Oregon tonight. Wind advisories are in effect
for the typically windy areas. The precip will pick up this
afternoon and shift south through the area into the evening--the
rain will probably start around 2pm in Seattle if the latest HRRR is
right. Monday looks like a pretty quiet day between weather systems.
On Tuesday the strong warm front we have been talking about arrives,
with sky high snow levels through the middle of the week.

.LONG TERM...After a pretty decent round of rain Tuesday and Tuesday
night--with some heavy rain in the mountains, the heavy precip will
be north of the area on Wednesday. There will still be rain at times
over Western Washington--but this lull on Wed will help a great deal
with the rivers. Then on Thursday the rainfall picks up again--but
precip amounts in the models are actually pretty modest.

&&

.AVIATION...A strong, windy, and wet cold front will gradually
slide southeast through Western Washington this afternoon and
evening. Strong southerly winds are expected before frontal
passage (fropa), then much lighter northwest wind expected
following fropa. Strong westerly flow above 100 through tonight. A
brief period of high pressure on Monday will lead to more benign
conditions on Monday afternoon.

KSEA...Deteriorating conditions today until a cold frontal passage
(fropa) around 05z. Rain will develop around 22z and get heavy
enough around 01z to 04z to reduce vsby. Cigs will fall rapidly
once rain begins. Strong low-level winds will precede the front.
S-SW winds at 2,000-foot will reach 50 knots in the hours
preceding fropa, and 4,000-foot winds will reach 65-75 knots.
Rain and low-level wind will ease quickly in the hours following
fropa. Haner

&&

.MARINE...A strong cold front extending WSW from central
Vancouver Island into the Pacific will slowly drag southeast down
the British Columbia coastline and then push southeastward
through the coastal and inland waters late this afternoon and this
evening. In advance of the front, southerly gales are either
occurring already or expected this afternoon. Once the front
passes, winds will rapidly ease and shift to the northwest behind
the front. Frontal passage timing and easing of wind will range
from about 3 PM near Cape Flattery to almost midnight at the south
end of Puget Sound.

High pressure will bring light winds to the waters on Monday. A
strong warm front will push northward through the waters on Tuesday.
A strong low pressure center developing well offshore will push
northeast into Haida Gwaii on Wednesday. Haner

&&

.HYDROLOGY...The Skokomish river in Mason county will probably get
up near flood stage tonight and Monday and there is a flood watch in
effect. The precip next week will be heaviest Tuesday and Tuesday
night, then there is a lull on Wednesday, and then it picks up a bit
Thursday but is not heavy. We will have to watch the rivers with the
very high snow level around mid-week, but the Skokomish River in
Mason county is the only one that is an obvious threat--if not
tonight and Monday, then certainly on Tuesday.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory until 10 PM PST this evening for
     Cascades of Whatcom and Skagit Counties.

     Flood Watch through Monday morning for Hood Canal Area-Lower
     Chehalis Valley Area-Olympics.

     Wind Advisory until 6 PM PST this evening for Admiralty Inlet
     Area-Central Coast-North Coast-San Juan County-Western
     Skagit County-Western Whatcom County.

PZ...Small Craft Advisory for rough bar until noon PST Monday for
     Grays Harbor Bar.

     Gale Warning until 9 PM PST this evening for 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 until 6 PM PST this evening for Admiralty Inlet-
     Coastal Waters From Cape Flattery To James Island 10 To 60
     Nm-Coastal Waters From Cape Flattery To James Island Out 10
     Nm-East Entrance U.S. Waters Strait Of Juan De Fuca-
     Northern Inland Waters Including The San Juan Islands-Puget
     Sound and Hood Canal-West Entrance U.S. Waters Strait Of
     Juan De Fuca.

     Small Craft Advisory until 3 AM PST Monday for Central U.S.
     Waters Strait Of Juan De Fuca.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.wrh.noaa.gov/sew/gafd/latest_webafd.html


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