Small Craft Advisory 294, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
900 AM PST Thu Nov 30 2017

.SYNOPSIS...A front will bring rain to the area today. Another
system will follow Friday. Then an upper level low will give showers
Saturday. A drying trend will begin Sunday. Strong high pressure
aloft will build over the region next week for drier weather.

&&

.SHORT TERM...Rain moved into Western Washington ahead of schedule
this morning. All areas have had or are having rain already. The
zones and grids have been updated to reflect earlier onset of rain
this morning. The rain will probably end sooner as well--on the
coast this afternoon and inland this evening. A clear back edge to
the front is visible on satellite imagery. Highs today will be in
the mid to upper 40s. Snow in the mountains will amount to 2-5
inches.

Rain from the next system will begin on the coast late tonight or
early Friday morning. Rain will spread into the Olympics and
northern zones during the day Friday, but the latest NAM holds off
rain from Seattle southward until Friday evening. If this trend
holds in other models, will make some changes to the forecast this
afternoon.

Rain Friday night will morph into showers on Saturday as an upper
trough moves over the area. The snow level will fall to 2000 feet or
so. The mountains could receive advisory amounts of snow Friday
night through Saturday. Highs Friday will be 45-50, and on Saturday
will be closer to 45. Burke

.LONG TERM...Previous discussion...Looking further upstream, an
upper ridge was building near the dateline this morning. This ridge
is what kicks the Gulf trough onshore Sunday and helps amplify the
flow pattern across the Pacific with a strong ridge building over
the region Monday through Wednesday. Northerly flow aloft behind the
inland moving upper trough will likely maintain a few lingering
showers Sunday with cool temperatures. Then conditions dry out next
week with the building upper ridge and low level offshore flow
developing. Freezing levels to rise above 9000 feet by mid week and
areas of fog likely to develop under the temperature inversion in
the usual fog prone areas like the south Sound and SW interior.
Buehner

&&

.AVIATION...Westerly flow aloft over Western Washington this
morning will continue through tonight. The frontal system over the
area at this time will move into the Cascades late today, and the
next system upstream will reach the area late tonight. There will
be some drying at mid and upper levels late today and this
evening, while the area is between systems, but in general the
air mass will be moist.

We have MVFR conditions over most of the area this morning in
widespread rain; cloud cover is mainly BKN-SCT020-030 OVC050-070
with areas of visibility 3-5SM -RA BR. Conditions could
deteriorate a bit more today but are likely to not change much on
the whole, followed by marginal improvement tonight.

KSEA...Southeast wind 6-12 kt, becoming south 5-10 kt late this
afternoon through tonight. The steady frontal rain will give way
to showers late this afternoon, but ceilings are likely to be in
the 015-025 range from mid afternoon through evening. McDonnal

&&

.MARINE...The front moving through Western Washington today is
bringing small craft advisory southerly winds to all marine zones
except the central Strait of Juan de Fuca and Puget Sound. For
some of the zones there will be a break between systems tonight,
but another round of small craft advisory winds will accompany
then next front moving across the area late tonight through
Friday night. In addition, combined seas will be 13 to 15 ft over
the coastal waters and around 12 ft at the west entrance Strait
of Juan de Fuca through Friday.

A weaker system will move across the forecast area Saturday. A
ridge will build over the area Sunday and Monday. McDonnal

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 3 PM PST Friday 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-Northern Inland Waters Including The
     San Juan Islands-West Entrance U.S. Waters Strait Of Juan
     De Fuca.

     Small Craft Advisory for rough bar until 3 PM PST Friday for
     Grays Harbor Bar.

     Small Craft Advisory until midnight PST tonight for East
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 3 PM this afternoon to 3 AM PST Friday
     for Central U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 3 PM PST this afternoon for Admiralty
     Inlet.

&&

www.weather.gov/seattle

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