Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 211042
Area Forecast Discussion
National Weather Service Seattle WA
242 AM PST Sat Jan 21 2017
.SYNOPSIS...An upper low will bring showers at times through the
weekend. High pressure aloft will result in mainly dry weather
.SHORT TERM...An upper low will be over the offshore waters today
and Sunday. A couple of short waves ejecting northeastward from
the upper low will bring showers at times through Sunday but
nothing very organized or significant. Short wave number one will
cause an uptick in showers this afternoon and evening. Short wave
number two will push through the area on Sunday. The offshore
upper low will shift south Sunday night and Monday with moisture
pulling away from the region and the chance of showers ending. The
mountains will pick up a few inches of snow with snow levels
below pass levels through the period. Schneider
.LONG TERM...A high amplitude upper ridge over the Pacific
Northwest will bring dry weather for the remainder of the week.
The GFS shows a bunch of low level beginning Monday night,
perhaps hinting at a fog ridge. Schneider
.AVIATION...An upper level and surface low offshore near 47N/131W
will drift north this afternoon while an upper level shortwave
trough wheeling around the low moves NE across W WA this afternoon
and this evening. The air mass is fairly moist and somewhat unstable
for scattered showers. Except for some patchy morning fog or
stratus, conditions are expected to remain VFR today with CIGS
predominantly BKN-OVC040-080. An occluded front will approach the
area tonight then move NE across W WA on Sunday.
KSEA...VFR conditions with CIGS BKN-OVC040-070 are expected to
continue through this afternoon. There will be a few showers at
times. Surface winds will be SE 4-8 KT. Kam
.MARINE...A surface and upper level low about 350 NM W of the WA
coast will move NW today. A surface trough wheeling around the
offshore low will move NE across W WA this afternoon through this
evening. SCA winds are expected to continue over the coastal waters
and parts of the inland waters.
A deep 962 MB surface low will move northward offshore along 130W
tonight then pause W of the WA coast on Sunday. The associated
occluded front will move NE across W WA on Sunday. The low is strong
enough to produce a gale over the coastal waters. A Gale Watch has
been issued this evening to address this. At this point the low
looks fairly compact and may be far enough offshore to limit the
inland waters to just SCA winds, although the E entrance to the
strait may come close. The low will depart the area to the S on
Monday. A weak surface ridge will remain over the area Tuesday
through Thursday for a period of weak winds.
A large westerly swell train around 19 feet is expected to reach the
WA coast today. The highest waves should reach the coast early this
morning then gradually subside during the late morning and
afternoon. The swell period is fairly long at 17-19 seconds so waves
hitting the beaches should pack a bit of energy. Offshore buoy 36
has started to pick up the swell train with 20 FT seas reported at
05Z and 08Z. A high surf advisory remains in effect for the coast
.HYDROLOGY...River flooding is not expected for the next 7 days.
WA...High Surf Advisory until 6 PM PST Saturday for Central Coast-
PZ...Gale Watch from late Saturday night through Sunday afternoon 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 4 PM PST Saturday for Central U.S.
Waters Strait Of Juan De Fuca-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-East Entrance U.S. Waters Strait Of Juan De Fuca.
Small Craft Advisory for rough bar until 4 PM PST Saturday for
Grays Harbor Bar.
Small Craft Advisory from 6 AM Saturday to 4 AM PST Sunday for
Northern Inland Waters Including The San Juan Islands.
Small Craft Advisory for hazardous seas until 4 PM PST Saturday
for West Entrance U.S. Waters Strait Of Juan De Fuca.
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