Gale Warning 11, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
309 AM PST Fri Jan 26 2018

.SYNOPSIS...A cool and unstable air mass will give showers to the
area through today. A frontal system associated with a low that
will track across northern portions of Western Washington on
Saturday will give rain and mountain snow tonight and Saturday,
and locally windy conditions late tonight and Saturday morning. A
warm front will lift north across the area Saturday night and
Sunday morning. The front will stall over southern British
Columbia on Sunday. A cold front will move through western
Washington on Monday.

&&

.SHORT TERM...Satellite imagery and area radars show showers with
a cool trough of low pressure lifting northeast across the area
early this morning. Behind the trough, showers will continue in
the cool and somewhat unstable air mass that is streaming into the
area from the eastern North Pacific. Snow levels in the mountains
will remain rather low (1500-2000 through tonight). A winter
weather advisory remains in effect through 6 PM PST this evening
for the Cascades of Pierce and Lewis counties above 2500 feet.

Satellite imagery shows a developing 1004 mb low near 43N 140W
early this morning that is moving rapidly to the east. This low is
expected to curl more northeastward later today through this
evening then slowly fill as it moves into northern portions of
Western Washington Saturday morning. Concerning mountain snowfall,
amounts are expected to be greatest over the Cascades of Pierce
and Lewis counties were a period of heavier snowfall will occur
later this evening through Saturday morning before tapering off.
The winter storm watch for this area above 2500 feet is being
converted to a winter storm warning for the likelihood of 1 to
2.5 feet of snow, with Paradise ranger station likely seeing
another 18 inches or so tonight through Saturday morning.
Concerning wind, the ECMWF is stronger with south-north pressure
gradients late tonight into Saturday morning than the GFS and WRF
solutions. A blend was used which results in a locally windy
forecast - but with winds remaining just below what would require
the issuance of a wind advisory.

A warm front will lift north across the area Saturday night then
stall from Vancouver Island into southeastern British Columbia on
Sunday. Models have become rather insistent that the front will
stall to the north of the forecast area as ridging builds over
California. This will lower the threat for significant flooding
across Western Washington with perhaps the exception of streams
and rivers flowing off the northern portions of the Olympic
Peninsula and in the Cascades of Whatcom County. In the mountains,
snow levels will rise to 6000-7000 feet south of the warm front,
but precipitation will decrease from the south. The forecasts
were updated to lower POPS over the southern two thirds of the
area Sunday and limit the heaviest rainfall to the far north.
Temperatures in the warm sector on Sunday will be mild, into the
50s in many locations. Albrecht

.LONG TERM...A period of heavy rainfall will spread south across
the area later Monday and Monday night as the frontal band over
southern portions of British Columbia drops back to the south.
Snow levels will fall back to around 2000 feet behind the front on
Tuesday.

From Tuesday through the remainder of the week, northwest flow
aloft with ridging developing offshore will gradually dry things
out but keep conditions cool with highs in the lowlands in the
mid 40s. Albrecht

&&

.AVIATION...Upper level shortwave disturbances will keep the
prospect for showers over Western Washington today...though
generally scattered as evidenced by radar imagery at the time of
this writing. Flow aloft will remain westerly today. Cigs over the
area a mixed bag of MVFR to VFR conditions with improvement to
mostly VFR conditions area-wide by late this morning and into the
afternoon...before dropping again this evening and tonight with
generally MVFR conditions expected then. The air mass remains moist
and slightly unstable.

KSEA...Above discussion applies. Given scattered nature of showers
expected through the day today...opted for VCSH to cover and any
shower may allow for cigs to drop into MVFR. Southerly winds 8-12
kts this morning and afternoon turning more southeasterly with
speeds 5-10 kts during the evening then returning to 8-12 kts
tonight.  SMR

&&

.MARINE...An approaching surface low will help to tighten gradients
over the coastal waters...keeping winds close to SCA criteria and
swells are expected to remain above 10 ft. That being said...while
winds may fall below criteria in the afternoon...opted to not get
too fancy with it and simply extend the inherited headline into this
evening. Winds look to pick up further tonight with gales possible
in both the coastal waters and the strait...and have posted a Gale
Watch to reflect that thinking. Small craft advisories may be needed
for the waters adjacent to the East strait...but will leave that for
the late morning package given that this may not be an issue until
very late tonight or Saturday morning. Keeping the weather
active...a slow moving front will affect the area Sunday and Monday.
SMR

&&

.HYDROLOGY...The Skokomish river has fallen below flood stage and
the flood warning was ended last evening.

The 00Z ECMWF and 06Z GFS solutions continue with the idea that
heavy rainfall with a frontal band will stall north of the
Canadian border on Sunday, then drop rather quickly southward
through Western Washington later Monday into Monday night. The end
result will most likely be less rainfall across the area than was
thought a couple of days ago.

At this time, the threat of any flooding will be most likely on
rivers flowing off the northern Olympic Peninsula and in the far
northern Cascades of Whatcom county. The normally flood prone
Skokomish River in Mason county is also at risk of flooding. Keep
in mind, however, that it would only take a small shift southward
for the flooding threat to increase across much of Western
Washington.

A flood potential outlook remains in effect for the area later
this weekend into early next week, and the threat of shallow
landslides is expected to increase for the next several days as
rainfall continues to fall onto increasingly saturated soils.
Albrecht

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory until 6 PM PST this evening for Cascades
     of Pierce and Lewis Counties.

     Winter Storm Warning from 6 PM this evening to 6 PM PST Saturday
     for Cascades of Pierce and Lewis Counties.

PZ...Gale Watch from this evening through Saturday morning for
     Central U.S. Waters Strait Of Juan De Fuca-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-Northern Inland Waters Including The San Juan
     Islands-West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 10 PM PST this evening 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 PST this evening
     for Grays Harbor Bar.

&&

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