Small Craft Advisory 81, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
916 AM PDT Thu Apr 6 2017

.SYNOPSIS...An upper level trough will bring areas of rain to
Western Washington this morning as it heads northeast toward British
Columbia. Rain will taper off by early afternoon behind the trough.
A strong frontal system will bring rain and windy conditions late
tonight through Friday night. A weak upper level trough will send
showers across the area on Saturday. Another frontal system will
arrive late Sunday. Unsettled weather will likely continue into
early next week.

&&

.SHORT TERM...A compact surface low associated with the upper level
shortwave trough moving across W WA this morning brought a short
burst of wind to parts of the W WA interior this morning. However,
winds are already decreasing. The next shortwave trough axis was
over NW Oregon at 15Z/8 AM and should be moving over B.C. by 21Z/2
PM. RADAR shows a large area of rain moving N across the W WA
interior this morning, but the rain was diminishing over NW Oregon
behind the trough axis. So a lull in precipitation this afternoon
with just some showers around looks on track.

The next strong frontal system was brewing W of the N CA coast at
15Z with a 987 MB surface low near 40N/137W. Models agree that the
deepening low will curve N then cross the WA offshore waters on
Friday as a 976 MB low. The main impact from this system will be
windy conditions over both the coast and parts of the interior. A
high wind watch is in effect for the coast on Friday. The 12Z GFS
showed some 35 KT wind barbs over the land areas of the San Juan
Islands on Friday so a high wind watch may be appropriate for parts
of the interior as well. Winds should decrease Friday night as the
low moves N toward N Vancouver island.

Rain from the associated cold front will spread N over W WA late
tonight then diminish behind the front Friday morning. Another batch
of rain associated with the upper level low should swing across the
area Friday afternoon.

A weak upper level trough will move E across W WA on Saturday for
scattered showers. Kam

.LONG TERM...Previous discussion from the 302 AM AFD...A brief
break in precipitation is possible Sunday as a ridge of high
pressure moves across the area. The break is most pronounced in the
00z run of the ECMWF. Another front will move through the area
Sunday night and will be followed by showers and onshore flow on
Monday. Another brief lull is possible on Tuesday before yet another
front approaches the area on Wednesday.
Albrecht

&&

.AVIATION...Another batch of rain was moving through the region this
morning as a small low pressure system moved north toward Vancouver
Island. The rain will turn to scattered showers and then there will
be a break in the weather tonight.
he

KSEA...Rain turning to scattered showers today, and a break in the
weather between systems tonight. Friday will be rainy and blustery
as a deep low tracks just offshore--the windy weather will be in the
afternoon and evening.

&&

.MARINE...A little low spun up and moved north through the coastal
waters overnight and is just off Vancouver Island this morning, that
was the system that I'd thought would end up disappearing into the
terrain. So that means this morning has been considerably blustier
in all the usual spots. Winds will decrease this afternoon and
evening for a break between systems. A deep low will move just
offshore Friday, with full gales in the afternoon and evening most
areas--and perhaps storm force over the coastal waters closer to the
low.

&&

.HYDROLOGY...2 to 3 inches of rain in 36 hours is expected from
late Thursday night through Friday night (00Z Fri-12Z Sat) over the
Olympics. This could drive the typically flood-prone Skokomish River
in Mason County above flood stage Friday night or Saturday. A Flood
Watch is in effect for the period from Friday morning through
Saturday afternoon.

Other rivers will see rises Friday through Saturday, but flooding
is not expected for the next 7 days. Kam

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Flood Watch from Friday morning through Saturday afternoon for
     Mason County.

     High Wind Watch from Friday morning through Friday evening for
     Central Coast-North Coast.

PZ...Small craft advisory coastal waters, entrances to the Strait,
      Admiralty Inlet, northern waters--all til 2pm.
     Gale watch coastal waters, entrances, northern waters for
      Friday through Saturday morning.

&&

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You can see an illustrated version of this discussion at
www.weather.gov/seattle/gafd/latest_webafd.html