Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

131
FXUS66 KSEW 172322
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
322 PM PST Fri Nov 17 2017

.SYNOPSIS...Weak high pressure will be over the area tonight and
Saturday. A strong front will reach the area Sunday--heavy rain
is likely in the Olympics, and windy weather is possible for some
areas. Periods of wet weather with rather mild temperatures are
likely next week--with windy conditions possible at times.

&&

.SHORT TERM...A little light snow shower activity will taper off and
conditions will be mostly dry with partly to mostly cloudy skies
through Saturday. A strong front will be hung up over the B.C. coast
and Vancouver Island Saturday and Saturday night and prefrontal
pressure gradients will pick up over Western Washington Saturday
night. Pressure gradients look strong enough for wind advisory
strength winds Sunday morning from around Admiralty Inlet north
through the San Juans and it should be windy on the coast, but not
too notable. There will be heavy rain in the Olympics and a decent
rain shadow in the lee of the Olympics--and then the rain will close
in over most areas in the afternoon and pressure gradients will
become light into the evening hours. The front is into Oregon by
late Sunday evening.

.LONG TERM...The front that moves through Western Washington Sunday
afternoon will be over Northern California and Oregon later Sunday
night and Monday morning. The GFS shows a dry day for Western
Washington on Monday. Rain moves back into Western Washington
Tuesday afternoon and evening. The heavier rain shifts to the B.C.
coast and Vancouver Island for Wednesday and Wednesday night then
back down through the area Thursday. It will become unusually mild--
the 700mb temp will rise to around 0c and 850mb temps will peak
around +9c. That does not bode well for the ski areas by the middle
of next week. The good news is that the models do not have
especially heavy rain, but that might change again and bears
watching.

&&

.AVIATION...A flat upper ridge axis will move eastward across
Western Washington on Saturday. A wet cold front will be spreading
down the B.C. coast on Saturday evening. Moderate northwest flow
aloft, becoming westerly this evening. The low-level air mass is
moist and unstable, but the instability will become shallower
tonight and Saturday, with some drying on Saturday morning.
Convective showers will continue to decrease in both coverage and
intensity through tonight. Moistness of the air mass will support
cigs in the 010-020 range across the interior late tonight, but then
low-level drying on Saturday, will help dissipate low clouds.

KSEA...Southerly surface wind for next 30 hours and beyond. Cigs in
the 030-040 range are most likely early this evening. Cigs may drop
below 020 for a time late this evening or overnight. Low-level air
mass will experience some drying on Saturday morning, so clouds
below 100 will dissipate Saturday morning. Few if any clouds below
100 from late Saturday morning into Saturday evening. Haner

&&

.MARINE...A cold front will move down the British Columbia
coast on Saturday night, then move southeast across the waters on
Sunday. The front will be preceded by increasing S-SE wind on
Saturday, with gales expected over much of the waters starting
Saturday night. Following frontal passage late Sunday, winds will
quickly ease on Sunday evening. A high pressure center will pass
across the waters on Monday with light wind. A strong warm front
will push northward through the waters on Tuesday. A strong low
pressure center should move northward well offshore to near Haida
Gwaii on Wednesday.  Haner

&&

.HYDROLOGY...Heavy rain will fall in the Olympics on Sunday so
that will drive the Skokomish river in Mason county up again.
Mild wet weather is likely from about Tuesday afternoon through
about Thursday of next week--possibly resulting in flooding with the
best chance again on the Skokomish.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Flood Watch from Sunday morning through Monday morning for Hood
     Canal Area-Lower Chehalis Valley Area-Olympics.

PZ...Small Craft Advisory from 3 AM to 3 PM PST 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.

     Gale Warning from 3 PM Saturday to 3 PM PST Sunday for Coastal
     Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm.

     Gale Warning from 3 PM Saturday to noon PST Sunday 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.

     Small Craft Advisory from 9 AM to 6 PM PST Saturday for Coastal
     Waters From Point Grenville To Cape Shoalwater Out 10 Nm.

     Gale Warning from 6 PM Saturday to 3 PM PST Sunday for Admiralty
     Inlet-Coastal Waters From Point Grenville To Cape
     Shoalwater Out 10 Nm-East Entrance U.S. Waters Strait Of
     Juan De Fuca-Northern Inland Waters Including The San Juan
     Islands.

     Small Craft Advisory from 3 AM to 6 PM PST Saturday for East
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from midnight tonight to 6 PM PST Saturday
     for Northern Inland Waters Including The San Juan Islands.

     Small Craft Advisory from 6 AM to 6 PM PST Saturday for
     Admiralty Inlet-West Entrance U.S. Waters Strait Of Juan De
     Fuca.

     Gale Warning from 6 PM Saturday to noon PST Sunday for West
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 9 AM to 3 PM PST Saturday for Puget
     Sound and Hood Canal.


&&

$$

www.weather.gov/seattle

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



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.