Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS66 KSEW 151157
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
357 AM PST Wed Nov 15 2017

.SYNOPSIS...Rain will change to showers today as the front over
Western Washington moves east. An offshore upper trough will
bring showery weather tonight and Thursday, then move inland
Thursday night. An upper ridge will be over the region Friday and
Saturday for relatively day weather, with rain returning on
Sunday. Dry weather is possible Monday, with rain again Tuesday.

&&

.SHORT TERM...A frontal band is moving across Western Washington
early this morning, bringing a solid swath of moderate to heavy
rain to the area. In addition winds are gusting to 30 to 40 mph
ahead of and along the front. The deep "parent" upper low remains
well offshore, centered near 50N/132W.

The front will continue its eastward movement, crossing the
Cascades into Eastern Washington this afternoon. The steady rain
will give way to showers behind the front. There is lots of
convection in the cool pool of air behind the front, so there
should be isolated thunderstorms over the coastal waters and near
the coastal zones of Western Washington. In general, though,
precipitation will be decreasing - along with winds - behind the
front.

The upper low will continue southeast tonight and Thursday for
showery weather, then weaken into an open trough as it moves
inland Thursday night. Highs Thursday will be near normal, in the
mid to upper 40s.

The winter storm warning for the Mount Baker and Mount Rainier
regions of the Cascades continues through 3 pm. Showery
precipitation with the snow level around 2500 feet will add up to
another 2 feet in those zones tonight through Thursday night. Snow
amounts will be considerably less in the Stevens Pass/Snoqualmie
Pass region of the Cascades, more like 6 to 16 inches total.

A flat upper ridge will move into Western Washington on Friday.
There will still be considerable moisture and a chance of light
showers. McDonnal

.LONG TERM...The upper ridge will move slowly east on Saturday,
and the models agree pretty well now that the warm front/southwest
fetch of moisture on the west side of the ridge will be aimed into
southern British Columbia. It could bring a little rain to the
coast and north interior of Western Washington on Saturday, but
the interior from roughly Seattle southward has a decent chance at
a dry day with some sun breaks. The frontal band will weaken as it
moves across the forecast area Sunday, followed by an upper ridge
on Monday, and then another frontal system on Tuesday. McDonnal

&&

.HYDROLOGY...The Skokomish River has been above flood stage since
Sunday evening. The heavy rain will drive it to a minor crest this
morning, and it will probably fall below flood stage tonight or
Thursday. We also issued a short term flood warning for the
Bogachiel River, but it looks now like it will crest just shy of
flood stage. In addition, the Satsop River - where a flood watch
is in effect - should remain below flood stage.

The rain expected this weekend, mainly Saturday night through
Sunday night, now looks like less of a flood threat. Certainly, it
could drive the Skokomish River above flood stage, but the threat
for other rivers in our forecast area looks rather slight.
McDonnal

&&

.AVIATION...Strong moist southwest flow aloft will continue
today and tonight. A slow moving cold front over the Olympic
peninsula will move inland and weaken today. The air mass is moist
and somewhat unstable. Strong southeasterly surface pressure
gradients will continue to produce windy conditions at times over
the area today. Winds will ease after the front dissipates tonight.

Rain has spread inland, but ceilings are generally still VFR 4-6k
ft. Ceilings seem likely to fall to MVFR around 15Z, with some
improvement in the afternoon. Gusty southerly winds 15 to 25 kt
will continue today, then ease tonight.

KSEA...Expecting at least several hours of MVFR ceilings, 2-3k
ft, 15Z-21Z, followed by VFR. Gusty southerly surface winds 15-25
kt will continue today and ease tonight. CHB

&&

.MARINE...A front over the Olympic peninsula early this morning will
move inland and dissipate today. Gales are likely in the eastern
strait and northern inland waters as the front passes, with small
craft advisory strength winds all other waters. There will probably
be some gale force winds in the outer coastal waters, as a deep low
north of the area moves toward Vancouver Island.

This low is forecast to move south along the Vancouver Island coast
Thursday, then dissipate off the Washington coast early Friday. A
weak ridge will cross the region later Friday. A strong front will
slowly approach this weekend. CHB

&&

.HYDROLOGY...The Skokomish River has been above flood stage since
Sunday evening. The heavy rain will drive it to a minor crest this
morning, and it will probably fall below flood stage tonight or
Thursday. We also issued a short term flood warning for the
Bogachiel River, but it looks now like it will crest just shy of
flood stage. In addition, the Satsop River - where a flood watch
is in effect - should remain below flood stage.

The rain expected this weekend, mainly Saturday night through
Sunday night, now looks like less of a flood threat. Certainly, it
could drive the Skokomish River above flood stage, but the threat
for other rivers in our forecast area looks rather slight.
McDonnal

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Storm Warning until 3 PM PST this afternoon for Cascades
     of Pierce and Lewis Counties-Cascades of Whatcom and Skagit
     Counties.

     Winter Weather Advisory until noon PST today for Cascades of
     Snohomish and King Counties.

     Flood Watch through this afternoon for Central Coast-Lower
     Chehalis Valley Area.

     Flood Watch until noon PST today for Eastern Strait of Juan de
     Fuca-North Coast-Olympics-Western Strait of Juan De Fuca.

PZ...Small Craft Advisory for rough bar until 10 AM PST Thursday for
     Grays Harbor Bar.

     Small Craft Advisory until 4 AM PST Thursday for Admiralty Inlet-
     Central U.S. Waters Strait Of Juan De Fuca-Coastal Waters
     From Cape Flattery To James Island Out 10 Nm-Coastal Waters
     From James Island To Point Grenville Out 10 Nm-Coastal
     Waters From Point Grenville To Cape Shoalwater Out 10 Nm-
     Puget Sound and Hood Canal-West Entrance U.S. Waters Strait
     Of Juan De Fuca.

     Small Craft Advisory from 4 PM this afternoon to 4 AM PST
     Thursday for Coastal Waters From Cape Flattery To James
     Island 10 To 60 Nm-Coastal Waters From James Island To
     Point Grenville 10 To 60 Nm-Coastal Waters From Point
     Grenville To Cape Shoalwater 10 To 60 Nm.

     Gale Warning until 4 PM PST this afternoon for Coastal Waters
     From Cape Flattery To James Island 10 To 60 Nm-Coastal
     Waters From James Island To Point Grenville 10 To 60 Nm-
     Coastal Waters From Point Grenville To Cape Shoalwater 10
     To 60 Nm.

     Small Craft Advisory from 10 AM this morning to 4 AM PST
     Thursday for East Entrance U.S. Waters Strait Of Juan De
     Fuca-Northern Inland Waters Including The San Juan Islands.

     Gale Warning until 10 AM PST this morning for East Entrance U.S.
     Waters Strait Of Juan De Fuca-Northern Inland Waters
     Including The San Juan Islands.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.wrh.noaa.gov/sew/gafd/latest_webafd.html


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.