Heavy Rain in Washington, November 2, 2023

Area Forecast Discussion
National Weather Service Seattle WA
340 AM PDT Thu Nov 2 2023

.SYNOPSIS...Cold front moving through Western Washington this
morning. Weak upper level trough crossing the area this afternoon
and evening. A temporary ridge of high pressure will move through
Friday morning. Rain out ahead of the next front arriving Friday
afternoon with rain continuing until the front moves through
Saturday afternoon. Another front for Sunday night/Monday morning.
Upper level trough moving through Tuesday with a weak ridge of
high pressure trying to build Wednesday.

&&

.SHORT TERM /TODAY THROUGH SATURDAY/...Satellite imagery shows
cold front close to the north coast early this morning with the
front trailing back off to the southwest. Rain over the entire
area early this morning with the heaviest rain along the southwest
slopes of the Olympics. Quinault has received 2.73 inches in the
last six hours ending at 3 am. Over the interior Seattle has
picked up 0.43 inches in the last three hours. Temperatures were
a couple of degrees either side of 50 over the interior with
temperatures near 60 along the coast.

Cold front moving through Western Washington this morning with
moderate to heavy rain for at least the first part of the morning
commute for the interior. Satellite imagery shows little in the
way of cold air behind the front so only a chance of showers in
the afternoon with some locations staying dry. Best chances for
showers will be in a quick developing convergence zone behind the
front in Northern Snohomish/Southern Skagit county. Breezy
conditions just ahead and with the front with gusts in the 25 to
35 mph over the interior later this morning into the afternoon
hours. Highs today near 60.

Shower activity continuing to decrease overnight as a deepening
low well offshore throws up a weak upper level ridge ahead of the
front. Ridge axis will be over the offshore waters by 12z Friday.
Air mass very moist in the lower levels but enough surface wind to
keep widespread fog from forming. With some clearing over the
southern portion of the area could see some fog development
overnight in the Southwest Interior. Lows tonight will be mild,
mid 40s to lower 50s.

Vertically stacked low offshore will continue to move northeast
Friday. Weather system associated with the low approaching
Western Washington Friday afternoon with rain out area of the
front spreading over the area. This system will be an atmospheric
river with the front tapping into the sub tropics. Precipitable
water values with this system similar to the one going on right
now with the core of the storm showing 1.6 to 1.8 inches. Highs
near 60.

Another wet night Friday night with the warm front over Western
Washington. Parent low getting down to near 980 mb but the low
center is well offshore to the northwest confining the breezy
conditions to the coast. Lows near 50.

Rain continuing Saturday until the cold front moves through in the
afternoon. Winds increasing just ahead and with the front with
another round of 25 to 35 mph gusts for the coast and the
Northwest Interior. Another mild day with highs near 60.

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...Extended models are in
good agreement with a pair of systems moving through later Sunday
and again later Monday. Upper level trough keeping showers in the
forecast for Tuesday. Both the GFS and ECMWF operational runs
showing some ridging and drying for Wednesday. Ensemble solutions
are not in line with the operational runs although the ECMWF
ensembles are showing a ridge just 12-18 hours later than the
operational run. Until there is a clearer signal will keep showers
in the forecast for Wednesday. High temperatures near or slightly
below normal through the period, in the mid 50s. Felton

&&

.AVIATION...A frontal system continues to push inland across
western Washington this morning, bringing widespread moderate to
heavy rain to the area terminals. Flow aloft remains westerly to
southwesterly. Conditions at area terminals are widespread MVFR
this morning, however have seen conditions drop to IFR and LIFR
in areas of moderate to heavy rain. Steady rain will continue
through the early morning hours before becoming more showery
between 13-15Z. Winds are gusty along the coast this morning
(particularly for KHQM). Expect winds to increase to 8 to 15 kts
for interior terminals this morning, becoming gusty to 20-25 kts
at times as the system moves through. Winds will then ease by the
evening hours. Showers generally look to taper through the afternoon,
though a weak PSCZ may linger across Skagit and Snohomish counties
into the evening. Conditions will then start to improve towards
VFR this evening, but expect ceilings to lower back towards more
widespread MVFR by early Friday. Areas of fog, especially for
terminals across the southern Sound, will be possible Friday
morning and could bring ceilings and visibilities back down to
IFR/LIFR for a few hours.

KSEA...MVFR in rain. Ceilings and visibilities may briefly lower
to IFR at times through the morning should heavier rain move
across the terminal. Southerly winds will increase to 8 to 12
knots, with gusts potentially reaching 20-25 kts at times through
the morning. Winds will ease through the afternoon and evening
hours. Conditions to improve back towards VFR by this evening,
before ceilings lower back to MVFR by early Friday morning. 14

&&

.MARINE...A frontal system will continue to make its way across
the area waters this morning. Gales will remain possible across
the coastal waters and East Entrance of the Strait of Juan de Fuca
through the early morning hours as this system moves inland.
Small Craft Advisories remain in place for the Northern Interior
Waters and Admiralty Inlet through early this morning as well.
Except for a push of westerly winds along the central and eastern
portions of the Strait (where a Small Craft Advisory has been
issued) in the wake of the front, expect winds to gradually ease
through the late morning and afternoon hours. Seas 8 to 10 feet
at 7 to 9 seconds persist across the coastal waters early this
morning, so have issued a Small Craft Advisory for the coastal
zones and Grays Harbor Bar through this afternoon. Seas then look
to subside to 6 to 8 feet tonight, before falling towards 5 to 7
feet on Friday.

High pressure will briefly build into the area waters tonight
into Friday for overall calmer conditions across the waters.
Another frontal system will move across the local waters Friday
night into Saturday and looks to bring another round of area
headlines - with latest probabilistic guidance indicating an
80-90 percent chance of gale gusts across the coastal waters and
Eastern Entrance of the Strait on Saturday. This will be followed
by yet another frontal system early next week. Seas across the
coastal waters look to build to 12 to 16 feet over the weekend and
look to remain above 10 feet through much of early next week. 14

&&

.HYDROLOGY...In the six hour period ending at 3 am stations along
the southwest slopes of the Olympics were reporting 1.25 to 2.75
inches of rain in the last six hours. Another four to six hours
of heavy rain forecast adding another 1 to 1.5 inches to the
total. Snow levels near 10000 feet early this morning will only
lower down to 7000 feet this afternoon behind the front. The
Skokomish River has been slow to respond to the heavy rain in the
Olympics but is showing some life in the last couple of hours.
Expect the river to rise rapidly for the rest of the morning with
the river cresting this afternoon close to flood stage. The flood
watch for Mason county remains in effect through tonight.

Even if the Skokomish does not flood this round the next system
for later Friday into Saturday will also produce heavy rain over
the Olympics. Snow levels will remain in the 7000 to 8000 foot
range. Another 2 to 3.5 inches of rain is forecast for the
Olympics during this time. The Skokomish River will not have long
to recede from this first event before the rain from the second
event arrives. The river will again have the potential to reach
flood stage Saturday afternoon.

Slightly different scenario for the third system in the series
later Sunday night into Monday morning. Rainfall amounts look to
be a little less, 2 to 3 inches, with snow levels a little lower,
around 5500 feet. On the flip side the river will be running high
already so it will not take too much to push it near flood stage
again Monday.

For the burn areas, hourly thresholds and 24 hour targets have a
small (10%-20%) but non-zero chance of being exceeded and
triggering flash floods/debris flows, but only for the Bolt Creek
Fire burn area today.

Felton/JBB

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Flood Watch through late tonight for Hood Canal Area-Lower
     Chehalis Valley Area-Olympics.

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

     Small Craft Advisory from 8 AM this morning to 2 PM PDT this
     afternoon for Central U.S. Waters Strait Of Juan De Fuca-
     East Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Warning until 8 AM PDT 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-East Entrance U.S. Waters Strait Of
     Juan De Fuca.

     Small Craft Advisory until 8 AM PDT this morning for Admiralty
     Inlet-Northern Inland Waters Including The San Juan Islands.

     Small Craft Advisory from 8 AM this morning to 5 PM PDT this
     afternoon 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.

&&