Small Craft Advisory 242, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
925 PM PDT Wed Oct 5 2016

.SYNOPSIS...Generally dry tonight and into Thursday morning for much
of Western Washington with showers continuing over the Cascades. A
combination of upper level and surface low pressure will bring
another round of rainfall to the area starting Thursday afternoon
and continuing into Friday. While there may be a brief break Friday
night...expect a generally wet and active pattern over the area into
the beginning of next week.

&&

.SHORT TERM...Upper level flow will turn zonal overnight and into
tomorrow...which is expected to help dry out most of the lowland
locations for a brief 6-12 hour window. An upper level low digging
down toward Vancouver Island will couple up with surface low
pressure over the Pacific to bring the next round of precipitation
to the area...kicking in for coastal areas by early afternoon
Thursday and spreading inland by Thursday evening. By the time this
system reaches the mountains Thursday night...will likely see first
significant accumulations of the autumn thus far...with amounts
ranging 6-12 feet. Fortunately...snow levels are expected to be
above 6000 feet...so none of the major highway passes will be
impacted. This looks to give way to a brief break in the action
Friday afternoon before a warm frontal system migrating northward
restarts the chances for precipitation Friday night into Saturday.

Temperatures Thursday and Friday look to be nearly identical with
highs in the upper 50s to lower 60s in lower elevations throughout
the CWA. Once the warm front passes Saturday...temps will climb into
the 60s with some interior lowland locations getting very close to
70.

Inherited forecast is holding together well...thus no updates
needed.  SMR

.LONG TERM...From 352 PM PDT Discussion...The biggest question for
Sunday will be how far north the warm front moves. The GFS and NAM
lift the warm front far enough north on Saturday night that rain
ends except near the Canadian border, with most of western
Washington remaining rain-free on Saturday night and Sunday.
Meanwhile, the ECMWF hangs the warm front across northwest
Washington on Saturday night and Sunday, forming a focus for an axis
of steady moderate rain. All models keep southwest Washington dry on
Saturday night and Sunday, so the biggest impact on the forecast is
from the Seattle area on north. Classic case for a 50 percent chance
of rain in the forecast.

On Monday and Monday night, a digging trough around 140W-150W will
result in an amplifying ridge over the Pacific Northwest,
providing the best chance for rain-free conditions in the next 7
days.

The trough eventually lifts northeast, opening the door for strong
and moist jet stream winds to nose into the Pacific Northwest
around the middle of next week. This could mark the beginning of a
stormy period. Haner

&&

.AVIATION...Light westerly flow aloft over Western Washington this
evening will continue tonight and Thursday morning with a weak,
flat upper ridge over the region. The flow aloft will increase and
back to southwest late Thursday as a Pacific frontal system
approaches the Pacific Northwest. The low levels of the air mass
will remain moist with a fairly dry air mass aloft. Mid and high
level moisture will increase late Thursday.

VFR conditions prevail across Western Washington this evening with
ceilings generally 060-090, and just scattered clouds in some
areas. Low level moisture will probably cause conditions to
deteriorate overnight, with several hours of MVFR ceilings 013-025
for several hours roughly 10Z-18Z. Conditions will improve late
morning and afternoon, although rain will reach the coast in the
afternoon and spread inland in the evening.

KSEA...Northwest wind 6 kt or less, becoming southerly 4-8 kt late
this evening. MVFR stratus is likely to develop later tonight and
Thursday morning. McDonnal

&&

.MARINE...Northwest flow will gradually weaken overnight and become
southerly Thursday. Marginal small craft advisory conditions will
continue over the coastal waters through this evening due to wind
and/or swell.

A frontal system will move through the forecast area Thursday
night and Friday. The gale watch remains in effect for the coastal
waters. Southeast wind could reach 35 kts at the east entrance to
the Strait where a watch is also in effect Thursday night. Small
craft advisory winds are likely to develop in most remaining
waters. Winds will begin easing on Friday but could remain near
small craft advisory strength in Puget Sound.

Weak high pressure will be over the region Saturday through
Monday. McDonnal

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Gale Watch from Thursday afternoon through late Thursday night
     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-East Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory until midnight PDT tonight 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 for rough bar until 10 PM PDT this evening
     for Grays Harbor Bar.

&&

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