Scientific Forecaster Discussion
fxus66 ksew 221602
Area forecast discussion
National Weather Service Seattle Washington
900 am PDT sun Oct 22 2017
Synopsis...showers and breezy conditions will taper today. Flooding
will continue on some area rivers. Snow levels will fall with a few
inches of new snow possible, mainly above the passes. Monday will
have a few showers in the mountains, and Tuesday will be dry. After
some light rain Wednesday, a stretch of dry weather should return.
Short term...radar shows showers, mainly in the mountains, while
the area of heavier rain has moved well into Oregon. Some areas of
clear skies have developed. River flooding will continue today but
most rivers have already crested or will soon. The snow level will
fall to around 5000 feet; a few inches of new snow are likely in the
mountains above that level. Highs today will be in the 55-60 range.
Monday and Tuesday now appear completely dry. There will be patchy
late night and morning fog. Highs both days will be in the low to
mid 60s. Burke
Long term...previous discussion...the GFS and European model (ecmwf) still bring a
weak front through the area Wednesday with some light rain across
much of the area. This system will be progressive and will not pose
any flood risk. Timing has shifted somewhat among models, with some
runs showing some precipitation by Tuesday night. But the best
chance will be on Wednesday. Not much change to the mid week
A strong upper ridge builds over the region Thursday and Friday.
This will provide a stretch of dry weather, probably lasting into
next weekend. Fog may become more widespread if the flow remains
light but otherwise, nicer weather appears on tap. Mercer
Hydrology...heavy rainfall that has fallen over the past 24 hours
has come to an end. Rainfall amounts were sufficient to give
flooding to many rivers flowing off the west slopes of the Cascades
from Snohomish County southward. Flooding is also occurring on the
Skokomish River in Mason County.
Flooding is still possible on lower reaches of the Snohomish river
later this afternoon as the flood waves on the Skykomish and
Snoqualmie move downstream. Minor to moderate flooding on other
rivers in southwestern and west central Washington as well as
flooding on the Snoqualmie and Skykomish rivers will gradually
recede. The Skagit River is rising but is expected to stay just
below flood stage.
With the heavy rainfall having come to an end, the Flash Flood Watch
for the burn scar area of eastern Pierce County has expired.
Soil moisture has been relatively dry below the surface since there
has not been enough rainfall accumulation over a long enough period
yet this wet season. While an isolated landslide is possible in
western Washington with any rainstorm, and especially with high
intensity rain, soil moisture conditions have not yet significantly
increased the landslide threat. Albrecht
Aviation...strong west flow aloft over western Washington this
morning will gradually ease and veer toward northwest through
tonight, as an upper ridge begins building offshore. The air mass
will gradually dry, especially at mid and upper levels, with low
level onshore flow turning weakly offshore tonight.
We still have scattered light showers and areas of scattered-bkn025
bkn045 this morning, but much of western Washington is scattering
out. The improving trend will continue today with widespread VFR
conditions by midday. Relatively clear skies and light winds
tonight, combined the moist ground, should lead to patchy fog in
the more fog-prone valleys late tonight and Monday morning.
Ksea...southwest wind 7-13 kt gusting 20 kt, easing this afternoon
and evening, becoming southeast 4-8 kt tonight. Occasional MVFR
ceilings in scattered-bkn022 cloud deck should give way to VFR
conditions with ceilings aob060 by midday. Mcdonnal
Marine...onshore flow today will turn weakly offshore late
tonight and continue through Tuesday, as a ridge builds over the
Pacific northwest. Small Craft Advisory winds this morning will
ease today; however, westerly swell 10 feet or higher will
continue over the coastal waters and at the West Entrance Strait
of Juan de Fuca through Monday.
A weak cold front will move southeast across the area on
Wednesday, with Small Craft Advisory winds over some marine zones.
Northerly flow will follow the front on Thursday as a ridge builds
over southern British Columbia. Mcdonnal
Washington...Flood Watch until 5 PM PDT this afternoon for Bellevue and
vicinity-Cascades of Pierce and Lewis counties-Cascades of
Snohomish and King counties-east Puget Sound lowlands-
Everett and vicinity-Seattle and vicinity-southwest
Pz...Small Craft Advisory for rough bar until 5 PM PDT Monday for
Grays Harbor bar.
Small Craft Advisory until 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.
Small Craft Advisory for hazardous seas from 5 PM this afternoon
to 11 PM PDT Monday 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
Small Craft Advisory until noon PDT today for central U.S.
Waters Strait of Juan de Fuca-East Entrance U.S. Waters
Strait of Juan de Fuca.
Gale Warning until 9 am PDT this morning for central U.S. Waters
Strait of Juan de Fuca-East Entrance U.S. Waters Strait of
Juan de Fuca.
Small Craft Advisory until noon PDT today for northern inland
waters including the San Juan Islands-Puget Sound and Hood
Small Craft Advisory until 11 am PDT this morning for West
Entrance U.S. Waters Strait of Juan de Fuca.
Small Craft Advisory for hazardous seas until 5 PM PDT Monday
for West Entrance U.S. Waters Strait of Juan de Fuca.