Gale Watch 51, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
901 AM PST Fri Nov 12 2021

.UPDATE...Rain across much of the area this morning with the
stream of moisture focused on Western Washington. Precipitation
will continue through the morning with rain tapering off this
afternoon as the front slides south. Rivers will rise and peak
today into Saturday (refer to hydro section). Drier weather
Saturday, with another potentially stronger AR event Sunday-Monday
for heavier rain (especially northern areas).

&&

.SYNOPSIS...Rain will continue through most of today with an
atmospheric river across the area. The moisture will shift south
as a front passes through, with a brief break in the rain expected
late Friday into early Saturday. However, another plume of deep
moisture will likely bring heavy rain back into parts of the
region Sunday and Monday. Cooler, and drier conditions the middle
of next week.

&&

.SHORT TERM /TODAY THROUGH SUNDAY/...Latest radar and satellite
imagery this morning depict a deep plume of moisture aimed
squarely across the Pacific Northwest this morning. Satellite
derived precipitation water values remain in excess of 1-1.25"
with the core of the moisture band. Rainfall amounts have been
rather significant over the last 24 hours, with large swaths of
2-3 inches across portions of the coast, Olympics, and Cascades.
Given the continued influx of moisture expected through the
morning, along the satellite observations suggesting an embedded
shortwave that will provide for some focused enhancement of
precipitation rates toward the time of the morning commute. Thus,
those on the roads this morning should again remain alert for
reduced visibility and the potential for urban flooding in areas
that are low-lying and/or have poor drainage. Also cannot rule out
an isolated lightning strike in association with these stronger
convective elements, though confidence in seeing more than a few
is very low.

For a more detailed discussion of hydrologic concerns, specifically
river flooding, see the hydrology section below.

Guidance remains in fairly strong agreement that the bulk of the
moisture will begin to shift south toward mid-afternoon and
through the evening as the cold front advances southward. This
will temporarily usher in a cooler air mass, but with only a few
residual showers at that point shouldn't see much in the way of
Cascade snow save for the highest peaks. Heights rise a bit, with
a brief break in the precipitation early Saturday. This should
allow some of the rivers to recede a bit. However, the next round
of moisture is then slated to arrive Saturday evening. With the
cooler air in place, snow levels will begin relatively low but
will rise quickly again as another plume of moist subtropical air
approaches. This could lead to a quick few inches of snow at Mt.
Baker and even Stevens Pass, but with abundant moisture and
rapidly rising snow levels it shouldn't amount to much or linger
too long. Warm frontal precip likely lingers into Sunday with
ensembles suggesting a focus across the Olympics and northern
Cascades. There's still a decent spread in terms of just how much
rainfall may fall with this next atmospheric river, but given that
many rivers may still be running high, there likely will be
renewed hydrologic concerns for the basins which end up under this
heavy band. Temperatures will generally remain mild Sunday and
Sunday night in this pattern.    Cullen

.LONG TERM /MONDAY THROUGH THURSDAY/...By Monday, guidance
continues to suggest the plume of deep moisture will still be over
the region but shifting south as the next cold front begins to
advance toward the region. This front will likely bring an end to
the steady rain and another rapid lowering of snow levels. With
abundant showers, expect to see a return of snow at the pass
elevations Monday night into early Tuesday. With ensembles
favoring another weak ridge toward midweek after this front, will
need to keep an eye on the potential for a few significantly
cooler nights across the region by Tuesday night and into the
midweek period with lows dipping well into the 30s and afternoon
highs only in the mid 40s across the lowlands.

&&

.AVIATION...Strong southwest flow aloft becoming westerly
tonight. A cold front will move across the interior of Western
Washington around midday. Widespread IFR/MVFR conditions and surface
visibilities reduced to 2-4SM at times in moderate to heavy rain
this morning will improve somewhat late this afternoon. A mix of
MVFR/VFR in scattered showers will follow the front into this
evening.

KSEA...IFR/MVFR ceilings in moderate rain continuing into the
afternoon. Some improvement expected this evening into the
overnight hours with ceilings hovering near MVFR thresholds in
decreasing shower activity. Surface winds S/SW 5 to 10 knots. 27

&&

.MARINE...Surface cold front moving across the waters today
producing little in the way of winds. A warm front will sweep across
the offshore waters late Saturday with rising winds over the coastal
waters. A series of frontal systems will cross the area over the
weekend into early next week with winds reaching small craft
advisory or gale criteria at times. Elevated coastal seas of 8 to 11
feet will gradually subside Monday into middle of next week.  27

&&

.HYDROLOGY...Atmospheric river event in progress this morning
over Western Washington. Rainfall amounts in the last 6 hours
ending at 9 pm/05z were in the 0.75-1.0 inch range in the
Olympics, Coast, Southwest Interior and the Cascades of Pierce and
Lewis county. Six hour rainfall amounts were lower over the
remainder of the area with 0.10 to 0.75 inches common. Rain rates
will remain in the current ranges through this morning before the
rain tapers off this afternoon. Snow level currently at least
6500 feet and will remain high through this afternoon, lowering to
3500 feet tonight into Saturday morning.

Flood warnings have already been issued for a number of rivers
across the area. Rivers will continue to rise today, peaking later
today into Saturday.

Another atmospheric river event is possible especially for the
northern portion of the area Sunday into Monday. This will again
put Western Washington rivers under pressure with the biggest
flood threats on the rivers from King county northward.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Flood Watch through Saturday afternoon for Admiralty Inlet Area-
     Bellevue and Vicinity-Cascades of Pierce and Lewis Counties-
     Cascades of Snohomish and King Counties-Cascades of Whatcom
     and Skagit Counties-Central Coast-East Puget Sound Lowlands-
     Eastern Strait of Juan de Fuca-Everett and Vicinity-Hood
     Canal Area-Lower Chehalis Valley Area-North Coast-Olympics-
     Seattle and Vicinity-Southwest Interior-Tacoma Area-Western
     Skagit County-Western Strait of Juan De Fuca-Western
     Whatcom County.

PZ...None.
&&

www.weather.gov/seattle

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SEATTLE WA
1236 PM PST FRI NOV 12 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1155 AM     FLOOD            RANDLE                  46.54N 121.95W
11/12/2021                   LEWIS              WA   DEPT OF HIGHWAYS

            WSDOT SW REPORTS THAT RIVER FLOODING OVER
            US12 IN BOTH DIRECTIONS HAS CLOSED THE
            HIGHWAY AT RANDLE AT 11:55AM UNTIL FURTHER
            NOTICE.

&&

JP