River Flood Warning 37, NWS Seattle, WA

687 
WGUS86 KSEW 290655
FLSSEW

Flood Statement
National Weather Service Seattle WA
1155 PM PDT Thu Oct 28 2021

...The Flood Warning continues for the following rivers in 
Washington...

  South Fork Stillaguamish River Near Granite Falls affecting 
  Snohomish County.

.The South Fork of the Stillaguamish river has crested near flood 
stage and will slowly recede overnight into Friday morning.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Turn around, don't drown when encountering flooded roads. Most flood 
deaths occur in vehicles.

Stay tuned to further developments by listening to your local radio, 
television, or NOAA Weather Radio for further information.

Caution is urged when walking near riverbanks.

Additional information is available at www.weather.gov.

The next statement will be issued by Friday morning at 645 AM PDT.

&&


WAC061-291345-
/O.EXT.KSEW.FL.W.0037.000000T0000Z-211029T1339Z/
/GFLW1.N.ER.211029T0156Z.211029T0300Z.211029T0439Z.NO/
1155 PM PDT Thu Oct 28 2021

...The Flood Warning is now in effect until tomorrow morning...

The Flood Warning continues for
  the South Fork Stillaguamish River Near Granite Falls.
* Until tomorrow morning.
* At 11:15 PM PDT Thursday the stage was 13.5 feet.
* Flood stage is 14.0 feet.
* The river will remain near flood stage into early Friday morning. 
* Forecast...The river is expected to fall to a foot below flood 
  stage Friday morning and will continue to recede Friday afternoon.
* Impact...At 14.0 feet, the South Fork Stillaguamish River will 
  cause flooding along the river and tributaries.  A stage of 14 
  feet corresponds to Phase 2 in the Snohomish County Flood Warning 
  System.
* Flood History...This crest compares to a previous crest of 13.5 
  feet on 01/26/2003.


&&

LAT...LON 4806 12191 4808 12204 4816 12211 4824 12214
      4816 12202 4815 12192

$$

44

791 
WGUS86 KSEW 291311
FLSSEW

Flood Statement
National Weather Service Seattle WA
611 AM PDT Fri Oct 29 2021

...The Flood Warning is cancelled for the following rivers in 
Washington...

  South Fork Stillaguamish River Near Granite Falls affecting 
  Snohomish County.

.Heavy rain came to an end over the North Central Cascades early 
Friday morning. Three to five inches of rain fell on Thursday. 
Lighter rain will continue this morning before the rain band drops 
south late this morning and this afternoon.

WAC061-291415-
/O.CAN.KSEW.FL.W.0037.000000T0000Z-211029T1311Z/
/GFLW1.N.ER.211029T0156Z.211029T0300Z.211029T0439Z.NO/
611 AM PDT Fri Oct 29 2021

...The Flood Warning for the South Fork Stillaguamish River Near 
Granite Falls has been cancelled...

The Flood Warning is cancelled for
  the South Fork Stillaguamish River Near Granite Falls.
* At 5:15 AM PDT Friday the stage was 11.2 feet.
* Flood stage is 14.0 feet.
* The river crested at 14.3 feet around 9 PM Thursday. 
* Forecast...The river is below flood stage and will continue to 
  recede today.


&&

LAT...LON 4806 12191 4808 12204 4816 12211 4824 12214
      4816 12202 4815 12192

$$

44

Area Forecast Discussion...UPDATED
National Weather Service Seattle WA
940 AM PDT Thu Oct 28 2021

Updated to add hydrology section

.SYNOPSIS...Rain will persist across the region through Friday
with heavy accumulations across the Olympics and Northern and
Central Cascades potentially yielding river flooding. Drier air
arrives late Friday with dry and cooler conditions for the weekend.
Active weather returns to Western Washington early next week.

&&

.SHORT TERM /TODAY THROUGH SATURDAY/...Forecast remains generally
on track this morning. The plume of deep moisture remains aimed
across the northern portions of the area this morning and will
gradually shift south through the day. Forecast was updated to
lower QPF across the southern portions of the area for this
morning, as it will be a few more hours before the steadier rain
arrives. Otherwise no additional updates needed this morning and
the previous short-term discussion follows below.   Cullen

Snow levels will rise to 8000 to 9000 feet by later this morning
with PWATs rising to 1" to 1.25". This will make conditions feel
relatively warm and muggy out, with temperatures rising into the
low 60s in some locations with dewpoints in the mid to upper 50s.
This environment will set the stage for efficient rainfall through
the day, with the heaviest rainfall accumulations occuring from
the Southwest Olympics to the Northern and Central Cascades.
Current NBM probabilities of rainfall accumulation exceedance in a
24 hour period for today are as follows:

*Olympics - Probability of exceeding 1": 90%
*Olympics - Probability of exceeding 2": 40%
*Olympics - Probability of exceeding 3": 10%
*Olympics - Probability of exceeding 4": 5%
*Olympics - Probability of exceeding 5": >5%
*North & Central Cascades - Probability of exceeding 1": 90%
*North & Central Cascades - Probability of exceeding 2": 60%
*North & Central Cascades - Probability of exceeding 3": 20-25%
*North & Central Cascades - Probability of exceeding 4": 10%
*North & Central Cascades - Probability of exceeding 5": 5%

In all, widespread rainfall totals in the aforementioned areas
exceeding 3 inches can be expected through Friday morning.
Confidence is increasing in a higher end totals in the North and
Central Cascades, with some areas potentially seeing 4 to 6 inches
of rain through tomorrow morning. Totals in the Olympics look to
range between 3 and 4 inches, with isolated totals to 5 inches.
Lowland areas can generally expect 1 to 2 inches, with the outer
coast likely seeing 2 to 3 inches. As a result, expect widespread
rises in rivers across the region, with the greatest threat for
river flooding outside of the Skokomish basin likely in northern and
central Cascade basins. Urban flooding will also be a concern,
especially under any bands of high rainfall rates and in areas with
poor drainage. Heavy rainfall rates could also pose a threat for an
isolated landslide or two across the area as soils become more
saturated over the next 12 to 18 hours. However, expecting this
threat to remain conditional on heavy rainfall rates at this time.
Refer to the hydrology section for specifics.

Breezy conditions are expected later this morning and early this
afternoon, as some of those stronger low-level jet winds get mixed
down to the surface. Note that stronger winds will be most likely
south of the heaviest band of rain, including much of the Puget
Sound region, extending southward toward the Chehalis Valley. Expect
gusts in the 30 to 40 mph range at times. Expect impacts across
these areas, including damage to trees and power disruptions.

Timing remains in sync across the current suite of model guidance in
the timing of a cold front bringing drier air to the region through
the day Friday. There likely will be a brief period of convergence
behind the front that will keep low clouds and possibly light
showers in the Central Puget Sound area through Friday afternoon
before clearing. Nonetheless, this will end heavy precipitation and
set the stage for drier weather and cooler overnight temperatures
for the weekend.

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...Dry and mostly sunny
conditions continue to look likely for the weekend as a shortwave
ridge axis slides across the region. Expect seasonal highs and
slightly cooler than normal overnight lows. Widespread 30s are not
out of the question early Saturday and Sunday mornings given the
current forecast for mostly clear skies. Late Sunday into Monday
will likely mark the return of active weather, with ensemble means
showing the next system approaching and bringing rain back to the
region early next week. Snow levels look lower given the cooler
airmass in place as the next system arrives, so some snow
accumulations may again be possible on Stevens Pass. Near seasonal
temperatures expected through the period.

Pullin

&&

.AVIATION...Westerly flow aloft through Friday evening. Rain across
much of the area this morning, heaviest rain located across northern
areas. MVFR/IFR cigs for most through the morning with areas of
LIFR. MVFR/IFR cigs through much of today with rain for lowered
vsbys at times in heaviest showers. Winds will increase through this
morning with southerly wind gusts of 25 to 30 kts possible for areas
through the day. Winds will taper off a bit tonight as a front moves
through the area.

KSEA...MVFR cigs with IFR cigs possible at times today. There will
be light to moderate rain through today, though a dry period is
possible late this morning into the afternoon, with the heaviest
rain tonight for lowered vsbys. Winds will increase this morning
with southerly wind gusts of 25 to 30 kts possible late morning into
the afternoon, tapering off as a front moves through. New guidance
is suggestive of the switch to north winds potentially holding off
until closer to mid morning tomorrow. Will put the rough estimate of
the timing in the 18Z TAF for planning purposes.

JD/Kristell

&&

.MARINE...Winds will increase through this morning with a front over
the area. Small Craft Advisory winds for the Coastal Waters, western
entrance of the Strait of Juan de Fuca, and Puget Sound for much of
the today with the front. Visibilities over most of the area waters
will be reduced at times in the heaviest bands of showers that will
move through the area today. Brief gales will be possible for the
central/southern coastal waters today, though mainly SCA winds are
expected. Winds will taper early tonight with increasing north winds
for the coastal waters Friday. Winds will be more easterly Saturday
into Sunday with SCA winds possible. Additional fronts will move
through the area next week for headlines. Swells of 10 to 12 feet
into Friday. JD/Kristell

&&

.HYDROLOGY...An atmospheric river is expected to bring widespread
moderate to heavy rain to Western Washington starting this evening
and persisting through Friday morning. Confidence is high in the
heaviest accumulations occurring from the Southwestern Olympics to
the Northern and Central Cascades, generally north of northern King
County. The current QPF forecast calls for at least 3 to 4 inches of
rainfall in the Olympics, 4 to 6 inches in the north and central
Cascades, with lesser amounts of 2 to 3 inches in the southern
Cascades and 1 to 2 inches in most lowland areas, except the
northern Olympic Coast. Widespread rapid rises in rivers will result
from these excessive rainfall amounts. Expect the greatest threat
for river flooding outside of the Skokomish basin to be in northern
and central Cascade basins (e.g. the Nooksack, Skagit,
Stillaguamish, Skykomish, and other basins. In addition, the snow
level will rise to over 9000 feet for most of the duration of the
precipitation resulting in most of the precipitation becoming storm
runoff into the rivers.

The severity of flooding will depend on the exact amount and
placement of rainfall accumulation which will in part be determined
by the direction of flow and the location of the core of the maximum
moisture plume in the atmospheric river. Some of the uncertainty
stems from how the moisture gets around or over the Olympic
Mountains. High end totals of up to 6 inches is not out of the
question, especially in the western slopes of the Central and
Northern Cascades. Minor to moderate flooding expected to continue
on the Skokomish River at Potlach through at least Friday night.

Urban flooding will also be a concern, especially under any bands of
high rainfall rates and in areas with poor drainage. Heavy rainfall
rates could also pose a threat for an isolated landslide or two
across the area as soils become more saturated over the next 12 to
18 hours. However, expecting this threat to remain conditional on
heavy rainfall rates at this time.

Drier air will push into the region on Friday, ending heavy rain by
at least Friday afternoon/evening. Rivers will continue to run high
on Friday, receding over the weekend.

Pullin/JBB

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Flood Watch through late tonight for Admiralty Inlet Area-
     Bellevue and Vicinity-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-
     Western Skagit County-Western Strait of Juan De Fuca-
     Western Whatcom County.

PZ...Small Craft Advisory until 5 PM PDT this afternoon for Grays
     Harbor Bar.

     Small Craft Advisory until 11 AM PDT Friday 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 until 6 PM PDT this evening for West
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 7 PM PDT this evening for Puget Sound
     and Hood Canal.

&&

www.weather.gov/seattle