NOAA Forecast Discussion
851
FXUS66 KSEW 160358
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
800 PM PST Fri Nov 15 2024
.SYNOPSIS...Increasing clouds this evening and tonight ahead of a
strong storm system that will enter the region on Saturday.
Widespread precipitation and breezy winds expected throughout the
weekend through Monday. Unsettled conditions are favored to continue
into Tuesday and Wednesday, with potential for cool and wet
conditions through the end of next week.
&&
.SHORT TERM /TONIGHT THROUGH MONDAY/...Current satellite shows high
clouds increasing over the western half of the CWA and should spread
over the remainder of the area as the night progresses. Temps as of
730 PM PST already on the chilly side with a lot of obs in the mid
to upper 30s. Seattle, Everett and Hoquiam are exceptions with temps
still in the lower 40s. Forecast dilemma of the evening given this
cooldown will be some pretty narrow temp/dewpoint spreads, which
under clear skies would result in fog...but with clouds incoming,
the challenge emerges in whether or not the timing of said clouds
will be enough to stave off fog development. While this does not
seem to be the case for some spots, such as the ever foggy south
Sound and Chehalis valley, the fact that obs with limited
visibilities are also popping up over the islands as well as
portions of northern Snohomish county suggest this will merit
additional monitoring should conditions deteriorate further.
Other than that, current forecast is on track with a very active
weather pattern ahead for the next several days. No changes or
updates planned this evening, unless fog development necessitates
it. For additional forecast details, please refer to the Previous
Discussion section below.
18
From Previous Discussion...Moist northerly flow will continue to
promote light shower activity over the mountains this afternoon and
evening as an upper level trough axis shifts eastward of the
Cascades. Below normal temperatures will persist today with highs
reaching the upper 40s for most of the lowlands. Satellite imagery
shows cloud cover increasing from the west as the next system
approaches, and cloud cover will continue to increase throughout the
overnight period ahead of incoming precipitation.
Another strong storm system will push into the Pacific Northwest
on Saturday, bringing in more widespread precipitation and breezy
winds through Monday. The primary impacts of this storm system
are outlined below:
* MOUNTAIN SNOW: A storm system will bring in significant
mountain snowfall over the weekend, with potential for 1 to 2
feet of snow above 2000 ft through Monday. The heaviest snow
will fall on Sunday into Monday, making travel through the
Cascade Passes difficult.
* COASTAL FLOODING: Coastal flooding will continue during high
tide periods along the Pacific Coast through the weekend, with
increasing potential for coastal flooding through interior
waters this weekend.
* RIVER FLOODING: The incoming precipitation will cause rises to
area rivers, and the Skokomish River is on track to enter Minor
Flood Stage by early Sunday. Other area rivers continue to be
monitored.
Precipitation will start to spread inland early Saturday, with
snow levels hovering near 2000-3000 ft. Snowfall over the Cascades
will quickly rise above 6000 ft as a warm front lifts across
western Washington throughout the day Saturday. Snowfall across
the Cascade passes will quickly change over to rain, producing
hazardous travel conditions with slushy road surfaces. Steady
precipitation will continue across the region ahead of an incoming
cold front that will cross western Washington mid-day Sunday and
lower snow levels back down to 2000 ft by Monday morning.
Precipitation over the mountains will transition back to snow,
with heavy totals expected through the passes. The heaviest snow
will fall on Sunday over the North Cascades, where Washington Pass
will see accumulations of 18 to 24 inches. Snow totals through
the passes will decrease moving southward, with totals between 12
and 16 inches through Stevens pass and up to 12 inches through
Snoqualmie Pass through Monday. With high confidence, the entire
western Cascade range has been upgraded to a Winter Storm Warning
above 2000 feet. The lowlands will also see significant
precipitation with this storm system, with totals reaching 1 to
1.5 inches between Saturday and Monday.
Lindeman
.LONG TERM /TUESDAY THROUGH FRIDAY/...From Previous
Discussion...Ensembles and operational forecast models have come
into better agreement over unsettled conditions continuing through
at least mid-week, with signals for an anomalously strong low
pressure system rapidly developing southwest of Vancouver Island
midday Tuesday into Wednesday. Depending on the exact track and
intensity of this low, coastal areas could see significant wind and
waves as this system evolves. With a large pressure gradient setting
up from the Pacific to eastern Washington, the chance for strong gap
winds through the Cascades exists at this time. Alongside potential
coastal hazards, the Cascade range will experience another round of
snow before warm air bumps snow levels above the major passes. For
the lowlands, this means a rainy regime for multiple days in a row
once again. Beyond this, early signals for late next week indicate
much uncertainty, with the best guess at this point being a wet
pattern with continued chances for precipitation existing on each
day through the end of the forecast period.
Knauss
&&
.AVIATION...Northerly flow aloft this evening, turning more
northwesterly on Saturday as incoming system pushes the current
ridge further eastward. Surface winds largely light and variable
this evening and overnight before turning south to southeasterly
late Saturday morning, with speeds increasing and becoming gusty.
The exception will be CLM, where winds will favor a more
southwesterly direction.
While most obs are showing VFR conditions, there are some swathes of
IFR/LIFR conditions worth mentioning. Fog and low clouds have
developed ahead of the incoming system for the eastern half of the
Olympic Peninsula, the adjacent islands and portions of the south
Sound area. This is spilling northward into SEA and BFI, although
only MVFR conditions are being reported there. As clouds move in,
these conditions may be limited to where they have already
developed, leaving most TAF sites largely unaffected though still
gradually sinking through the night. Locations currently VFR likely
to retain said conditions through late Saturday morning, with more
widespread MVFR to IFR conditions expected with incoming precip.
KSEA...Conditions bouncing around between VFR and MVFR this evening
with the hopes that incoming high clouds should help the terminal
settle in to a more consistent VFR setting. Late morning should see
cigs fall enough to enter into more consistent MVFR conditions which
will remain in place for what is left of the TAF period. Light south
to southeasterly winds expected throughout the TAF period with
speeds generally remaining below 5 kts. Speeds pick up a little by
18Z, turning more southerly and ranging 4-8 kts.
18
&&
.MARINE...Surface ridging will shift inland later tonight as a warm
front enters Saturday afternoon followed by a cold front late
Saturday night into Sunday morning. Previous Gale Watches have been
upgraded to warnings over the coastal waters and East Entrance of
the Strait. An additional Gale Warning has been issued for Admiralty
inland as these areas are slated to see strong southerly winds
Saturday/Saturday evening. Small craft advisories have been issued
for the remainder of the waters for the period Saturday through
early Sunday. All of these headlines remain in place with no
alteration. Brief surface ridging builds over the waters later
Monday into Monday night. Models are beginning to show the
possibility of a very stout sub-950 millibar surface low bombing
over the offshore waters Tuesday/Tuesday night. Confidence in the
track and strength of this system is low at this stage, but it is
likely, at a minimum, to generate some pretty large seas (20+ feet)
in addition to other hazards such as very strong winds, possibly
near Storm Force strength over the coastal waters.
McMillian/18
&&
.HYDROLOGY...From Previous Discussion...Rivers are settling down now
and will continue to recede for the next 24 to 30 hours.
Another system will move into the region Saturday into early Monday,
bringing more widespread precipitation to the area. Lowlands could
see up to an inch and mountains 2 to 6 inches of precipitation as
the models have slightly increased the QPF. Snow levels will
fluctuate quite rapidly, with snow levels rising up to 5000-7000 ft
Saturday then back down to 2000-4000 ft on Sunday. Expect rises on
area rivers, with the largest rises again expected on the rivers
flowing off of the Olympics and the north and central Cascades.
Currently, with the precipitation is spread out over more than two
days, no river flooding is expected outside of the Skokomish
river, which may return to minor flood stage by Sunday. Flooding
potential will depend on temperatures, QPF, and snow levels during
the heaviest precipitation and will continue to be monitored over
the next few days. The weather pattern looks like it will
continue to bring periods of precipitation through next week.
Bower
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Coastal Flood Advisory from 4 AM to 10 AM PST Sunday for
Admiralty Inlet Area-Bremerton and Vicinity-Everett and
Vicinity-Hood Canal Area-San Juan County-Seattle and
Vicinity-Southwest Interior-Tacoma Area-Western Skagit
County-Western Whatcom County.
Flood Watch from Saturday evening through Sunday afternoon for
Hood Canal Area-Lower Chehalis Valley Area-Olympics.
Coastal Flood Advisory from 10 AM to 5 PM PST Saturday for
Eastern Strait of Juan de Fuca-Western Strait of Juan De
Fuca.
Coastal Flood Advisory from 10 AM to 5 PM PST Sunday for Eastern
Strait of Juan de Fuca-Western Strait of Juan De Fuca.
Coastal Flood Warning from 9 AM to 4 PM PST Saturday for Central
Coast-North Coast.
Coastal Flood Warning from 9 AM to 4 PM PST Sunday for Central
Coast-North Coast.
Winter Storm Warning from 10 AM Saturday to 10 PM PST Monday for
West Slopes North Cascades and Passes-West Slopes North
Central Cascades and Passes-West Slopes South Central
Cascades and Passes.
PZ...Small Craft Advisory from 6 AM Saturday to 1 AM PST Sunday for
Central U.S. Waters Strait Of Juan De Fuca-West Entrance
U.S. Waters Strait Of Juan De Fuca.
Gale Warning from 8 AM Saturday to 1 AM PST Sunday for East
Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland
Waters Including The San Juan Islands.
Gale Warning from 6 AM Saturday to 1 AM PST Sunday for Admiralty
Inlet.
Small Craft Advisory from noon Saturday to 4 AM PST Sunday for
Puget Sound and Hood Canal.
Gale Warning from 6 AM to 7 PM PST Saturday 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.
&&
$$
NWS SEW Office Area Forecast Discussion
