Small Craft Advisory 236, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
900 PM PDT Wed Oct 31 2018

.SYNOPSIS...Light rain will fall at times tonight through Thursday.
More weather systems will move across western Washington Thursday
night into Friday, and again Sunday, giving wet weather and breezy
conditions.

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.SHORT TERM...Light rain or drizzle has been observed around the
area this evening. Most lowland spots around Puget Sound have had
only a hundredth of an inch or two in the last six hours. The
Seattle area seems to have had only a trace of rain. It's still
raining in the mountains.

A weather system moving through southern British Columbia on
Thursday will enhance rainfall in the north Cascades, and it will
also rain in the north interior. Mesoscale models are pretty dry
over the south interior.

Some areas will likely see a break in the precipitation Thursday
evening (and potentially a few breaks in the clouds) before next
system moves in overnight into Friday morning. This will bring more
rain across the entire area, heaviest in the Olympics and north
Cascades. Breezy southerly winds will also accompany the Friday
system with a few gusts of 20-25 mph possible across the lowlands.
With both the Thursday and Friday systems, snow levels will remain
rather high so not expecting any impacts snow-wise. As the trough
exits later Friday, most areas should see a break in precipitation
for Friday night into Saturday morning. High temperatures will be 55-
60 Thursday and Friday, falling to around 55 Saturday. CHB

.LONG TERM...Previous discussion...Yet another system arrives
sometime later on Saturday into Sunday. There are still some timing
differences between the GFS and ECMWF to work out, but widespread
rain should return by Saturday evening, continuing into Sunday.
Amounts look similar to Friday's storm but could change over the
next few days. Past Sunday, forecast remains uncertain. ECMWF keeps
showers going for most of Monday with another shortwave dropping
down while the GFS advertises a bit of a break Monday and then
another decently wet storm Monday night into Tuesday. Snow levels
may drop a few thousand feet with this round. For the sake of
consistency, have continued a blended approach to the forecast which
keeps showers for Monday and Tuesday. By Wednesday, both models
indicate ridging building which may provide a more noticeable break
in the active pattern. Stay tuned! CEO

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.AVIATION...Moist northwest flow aloft will continue tonight and
Thursday. Light gradients tonight will become increasingly southerly
on Thursday. The air mass is moist and stable with some light rain
or drizzle at times. Ceilings have been around 1k ft or lower all
day, and are not likely to improve tonight. Some IFR is likely as
well. The mountains will remain obscured. Brief improvement is
possible for a few hours Thursday afternoon.

KSEA...Discussion above applies. Southerly wind 8-12 kt. CHB

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.MARINE...Small craft advisory strength westerlies have been
observed in the strait since around 2 PM this afternoon. Re-issued
the advisories for the central and east strait earlier. Winds are
light elsewhere.

A frontal system moving into British Columbia on Thursday will sag
south into Washington on Friday, so gradients will increase Thursday
into Friday. Another frontal system will arrive around Saturday
night or Sunday morning. At least small craft advisory strength
winds are likely with these systems. CHB

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.HYDROLOGY...Periods of rain and moderately high snow levels through
the end of the week will continue to bring river levels higher. The
forecast total accumulation of rainfall in the mountains from today
through Sunday is 3 to 6 inches. However, recent models runs have
trended toward lower precipitation amounts and larger breaks between
storms. These latter effects would lessen the chance for flooding.
The current thinking is that strong river rises are likely with some
flooding not out of the question toward the end of the week. This
would mainly be for rivers in Snohomish County northward.

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.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 11 PM PDT this evening for Central
     U.S. Waters Strait Of Juan De Fuca-East Entrance U.S.
     Waters Strait Of Juan De Fuca.

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