Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 181016
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
216 AM PST Sat Jan 18 2020

.SYNOPSIS...A weather system will continue to bring lowland rain
and heavy mountain snow to the area today. Additional systems are
likely next week with lowland rain and mountain snow.

&&

.SHORT TERM /TODAY THROUGH MONDAY/...A cold front will move across
the area today. Precipitation associated with the system has moved
inland overnight, reaching the Cascades. At the surface,
temperatures are above freezing in most locations, allowing it to
fall as rain (a welcome return for those tired of the snow). The
exception remains around the Hood Canal where observations and
social media reports that a rain/snow mix or all snow is falling
with light accumulations. This should change over to rain into
the morning hours. Further north, temperatures remain just below
freezing in western Whatcom county. Precipitation has been slow to
advance up there, but suspect snow will begin shortly. Some
question as to how long this will last before the moisture fades
but enough concern to leave current headlines in place for here
and around the Hood Canal.

In the Cascades, snow levels will rise but still remain below
pass levels with good orographic lift promoting a period of heavy
snow today. Snow will continue post frontal passage into the
afternoon and evening hours. Winter Storm Warning remains in place
and travel is expected to be difficult at times, especially
during period of heaviest snowfall this morning. Travelers are
encouraged to alter their plans or check WSDOT road conditions
before they go and be prepared for hazardous conditions.

Precipitation turns more showery later Saturday afternoon into
evening, providing a break for most locations as upper level
ridging attempts to build in from the southwest. A warm front will
then brush north across the area Saturday night into Sunday with
scattered showers with heaviest amounts across the Olympic
Peninsula. Snow levels may also rise above pass levels (certainly
above Snoqualmie), limiting impacts to cross-Cascade travel. On
the plus side for those wishing for warmer weather, high
temperatures on Sunday could near the 50 degree mark.

Trailing cold front then crosses on Monday. Models continue to
disagree on strength of the front by the time it makes its way
onshore with best chance for widespread precipitation across the
Olympic Peninsula again. Snow levels may fall to near pass levels
but ensembles indicating not much moisture left by that point.
Still doesn`t look like anything too impactful but will keep an
eye on trends.

CEO

.LONG TERM /TUESDAY THROUGH FRIDAY/...Unsettled weather continues
for the rest of the week with systems moving across the area every
day or two. Looks like more typical PacNW winter pattern with
lowland rain and mountain snow. First system arrives sometime
Tuesday into Wednesday. Models continue to indicate heaviest
moisture may split the area, going north into BC and south
somewhere near the Oregon/NorCal border. For now, have not made
many changes to the forecast from that point on as blend covers
the ensemble spread well.

CEO

&&

.AVIATION...Southwesterly flow aloft becoming more westerly by this
afternoon. Surface flow has generally been easterly or southeasterly
so far this morning and while it may become more southerly to
southwesterly mid-morning through afternoon...is expected to revert
back to this easterly/southeasterly direction by late
afternoon/early evening. The exception to this being KBLI and
vicinity...with winds there remaining from the northeast before
becoming more easterly once the front moves through.

Cigs mostly VFR thanks to this easterly/southeasterly flow and the
drier air that accompanies it...although some isolated MVFR sites
are present. Rain making its way eastward with incoming front may
drag cigs down at times into MVFR...but winds returning to E/SE this
afternoon will keep cigs up mainly in VFR territory. While the NE
wind direction will help KBLI remain generally VFR also...the cold
temps associated with such a surface flow mill mean that precip
there may start off as snow before direction shifts more
easterly/southeasterly and thus transitioning to rain around mid-
morning.

KSEA...Cigs right around 3000 ft and as such running borderline
VFR/MVFR. Incoming precip may cause conditions to dip down into MVFR
at times this morning but once front passes through cigs should
rebound to VFR by afternoon. Southeast winds 7 to 12 knots becoming
southerly late this morning and remaining there for the remainder
of the TAF period. 18

&&

.MARINE...A passing strong frontal system will keep gales around
most area waters into this afternoon before beginning to taper off.
As such...have added SCA headlines for most waters in the post gale
afternoon/evening periods before things finally drop under any
headline criteria Meanwhile, seas at the Coastal Waters will linger
around 13-19 feet before subsiding on Sunday. East to southeast flow
will remain in place into early next week with low pressure
offshore. 18


&&

.HYDROLOGY...A period of heavy snow followed by rain later today
will cause rises on the rivers flowing off the Olympics. For now,
flooding is not expecting but will be keeping on eye on the
flood-prone Skokomish due to rainfall total and potential melting
of low elevation snow in the valleys.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Storm Warning until 4 PM PST this afternoon for Cascades
     of Pierce and Lewis Counties-Cascades of Snohomish and King
     Counties-Cascades of Whatcom and Skagit Counties.

     Winter Weather Advisory until 4 AM PST early this morning for
     Hood Canal Area.

     Winter Weather Advisory until 7 AM PST this morning for Western
     Whatcom County.

     Wind Advisory until 10 AM PST this morning for Admiralty Inlet
     Area-San Juan County-Western Skagit County-Western Whatcom
     County.

     Wind Advisory until 6 AM PST early this morning for North Coast.

     Winter Storm Warning until 4 PM PST this afternoon for Olympics.

PZ...Small Craft Advisory from 4 AM early this morning to 10 AM PST
     Sunday for Grays Harbor Bar.

     Small Craft Advisory from 10 AM this morning to 4 AM PST Sunday
     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.

     Gale Warning until 10 AM PST this morning 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-West Entrance U.S. Waters Strait Of
     Juan De Fuca.

     Small Craft Advisory from 4 PM this afternoon to 4 AM PST Sunday
     for East Entrance U.S. Waters Strait Of Juan De Fuca-
     Northern Inland Waters Including The San Juan Islands.

     Gale Warning until 4 PM PST this afternoon for East Entrance
     U.S. Waters Strait Of Juan De Fuca-Northern Inland Waters
     Including The San Juan Islands.

     Small Craft Advisory from 10 AM this morning to 10 PM PST this
     evening for West Entrance U.S. Waters Strait Of Juan De
     Fuca.

     Gale Warning until 1 PM PST this afternoon for Admiralty Inlet-
     Central U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 1 PM this afternoon to 4 AM PST Sunday
     for Admiralty Inlet.

     Small Craft Advisory until 4 AM PST Sunday for Puget Sound and
     Hood Canal.

&&

$$

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