Small Craft Advisory 272, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
948 AM PST Fri Nov 11 2016

.SYNOPSIS...An upper level ridge and low level offshore flow will
produce dry and mild weather this morning. A cold front will
spread rain onto the coast on this afternoon, then across the
rest of western Washington tonight and Saturday morning. Another
frontal system will bring rain Sunday afternoon through Monday
morning. Unsettled weather will continue the first half of next
week, followed by cooler and more settled weather in the second
half of next week.

&&

.SHORT TERM...A front is hung up off the coast today, with rain
mainly affecting the North Coast. An upper disturbance ---
currently west of the far northern California coast --- will move
north-northeast this afternoon and tonight, giving the front the
shove it needs to spread rain into western Washington. In
addition, the upper disturbance will help to spin up an elongated
1000-1004 mb low center that will move northeast across central
Vancouver Island on Saturday morning. This will tighten pressure
gradients over western Washington, first from the southeast early
Saturday morning, then from the southwest by early afternoon.
With peak wind gusts expected to be near 45 mph for the more
wind-prone areas, a marginal Wind Advisory is in effect for the
coast, the San Juan Islands, and the Bellingham area for the
southeast winds. Once southwest gradients take over, the OLM- BLI
gradient is forecast to peak near +5 to +6 mb around 1 pm, and 925
mb winds near 40-45 kts in cold advection could bring some peak
wind gusts around 40 mph in the Puget Sound region.

Should be a break in the rain and wind on Saturday night. Then a
more open front will slowly sag across the forecast area on
Sunday PM. Respectable south-southeast gradients will precede the
front, leading to a similarly windy round of weather on Sunday as
tomorrow for the coast and north interior (less so over the Puget
Sound region). Should see some heavy rain at times on Sunday
afternoon and Sunday night as well. 	Haner

.LONG TERM...From Previous Discussion: Extended models in pretty
good agreement early in the period with the cold front moving
through Western Washington on Monday. The ECMWF is a little slower
than the GFS kicking the front east of the area on Monday. Model
solutions become inconsistent later Monday with the GFS bringing
another wet system into the area while the ECMWF digs a trough
well off the coast. The GFS brings another system in Tuesday
afternoon. The ECMWF is slower and stronger with this feature.
There is some agreement at the end of the period with a cool upper
level trough moving into the area. The trough has the potential to
lower snow levels below all of the passes but the moisture with
the trough is limited. With the inconsistent model solutions have
gone more with climatology for the middle days of the extended,
which this time of year is likely pops and stayed with the lower
pops at day 7. Felton

&&

.AVIATION....Southwest flow aloft will continue today, then turn
more southerly tonight as an upper level trough approaches the
coast. At the surface, light southerly gradients today will increase
tonight. The air mass is stable and moist at mid and upper levels
with patchy fog this morning.

KSEA...High clouds will probably inhibit much in the way of fog or
low stratus this morning. Mid clouds will increase by evening, then
light rain will arrive after midnight with VFR stratus. Light
southerly wind will increase to 8-12 KT tonight. CHB

&&

.MARINE...A slow moving frontal system will bring southeasterly
small craft advisory strength winds to the coastal waters today.
Surface low pressure is forecast to develop and move northeast
across the waters tonight with gale force south-southerly winds
expected. Gale force southerly winds are possible later tonight and
early Saturday at the east entrance and over the northern inland
waters as the low moves inland. A burst of westerly gales could also
occur in the central and east strait Saturday morning. A gale watch
remains in effect for north inland areas with a little more
uncertainty as to timing and strength of wind speeds.

Post frontal southwesterly gradient will also develop across Puget
Sound with small craft winds 20 to 30 KT possible on Saturday.
Another strong front is possible Sunday. CHB/dtm

&&

.HYDROLOGY...A frontal system Sunday afternoon and Sunday night
will produce 2 to nearly 4 inches of rain in the Olympics. This could
potentially cause flooding on the flood-prone Skokomish River
Sunday night into Monday morning. Otherwise, river flooding is not
expected for the next 7 days.

USGS landslide indices have now fallen just below thresholds for
the occurrence of shallow landslides, based on rainfall data at
Puget Sound area airport stations. However, locations further
north toward Bellingham and along the coast have received
considerably more rain in recent days and likely still carry a
landslide threat in favored locations. Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Wind Advisory from 6 PM this evening to 6 AM PST Saturday for
     Central Coast-North Coast.

     Wind Advisory from midnight tonight to noon PST Saturday for San
     Juan County-Western Whatcom County.

PZ...Small craft advisory coastal waters today.
     Gale warning coastal waters tonight.
     Gale watch east entrance, and northern inland waters late tonight
     through early Saturday morning.
     Small craft advisory for hazardous seas west entrance to the Strait
     through tonight.
     Small craft advisory for rough Grays Harbor bar through tonight.

&&

www.weather.gov/seattle

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