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 202309
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
309 PM PST Fri Jan 20 2017

.SYNOPSIS...A broad upper level trough will remain over the
offshore waters through the weekend. A series of systems rotating
around it will bring showers and breezy conditions at times to
Western Washington along with seasonable temperatures. By early
next week, a ridge of high pressure will build into the Pacific
Northwest for the possibility of several dry days.

&&

.SHORT TERM...I have added a chance of showers back into the north
interior since the latest HRRR runs have shown light showers for
that area tonight and the latest radar data shows showers
approaching the area.

The pressure gradients across the Cascades are dropping again and
breezy conditions over the Cascade foothills and passes should
subside. The Seattle to Wenatchee gradient has dropped below 6 mb
as of 3 PM PST.

A broad upper trough and its associated stacked surface lows
continue to spin offshore through late Sunday, bringing showers
into the area. I have added a slight chance of thunderstorms into
the coastal waters for Saturday afternoon since there looks to be
a decent amount of energy as well as upper level support. Any
thunderstorms will be short lived. Sunday will bring the best
chance for steadier precipitation as a frontal system associated
with one of the surface lows moves through the area.

On Monday the upper trough will move south into the California
coastal waters and any lingering showers will dissipate over
Western Washington. I have removed precipitation from many areas
for Monday since models have been consistent in showing a drier
trend. JSmith

.LONG TERM...A ridge will begin to build in over the area late
Monday through at least Wednesday. Beyond that, model solutions
diverge with the GFS showing a drier solution continuing and the
ECMWF showing a few systems moving through the area bringing
showers. The GEM shows precipitation on Thursday but then a return
to dry conditions in its seemingly usual middle-ground stance.
JSmith

&&

.AVIATION...An occluded front will spread light rain to the area
this evening, mainly the coast and southwest Washington. The flow
aloft is southerly. Surface flow is E/NE and ceilings are mainly
VFR. Patchy fog may form in south sound overnight. An upper level
trough will maintain showers as it moves inland on Saturday. 33

KSEA...N/NE surface flow with VFR conditions. Light rain in the
vicinity this afternoon and evening. 33

&&

.MARINE...An occluded front with bring easterly Small Craft
Advisory winds to the Coastal Waters and Strait of Juan de fuca
tonight. Meanwhile, west swells will rise to 16-22 ft, peaking on
Saturday. A 960-965 mb surface low will track along 130W late
Saturday night with another occluded front moving inland on
Sunday. This front may produce gale force winds over the Coastal
Waters. The flow over Western WA will turn offshore early next
week as the surface low weakens and drifts south offshore. 33

&&

.HYDROLOGY...The Skokomish River continues to recede and is
expected to fall below flood stage this evening. No additional
flooding is expected at this time with only showers in the short
term forecast and then a switch to drier conditions starting
Monday. JSmith

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...High Surf Advisory from midnight tonight to 6 PM PST Saturday
     for Central Coast-North Coast.

PZ...Small Craft Advisory until 4 PM PST Saturday for Central U.S.
     Waters Strait Of Juan De Fuca-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 for rough bar until 4 PM PST Saturday for
     Grays Harbor Bar.

     Small Craft Advisory for hazardous seas until 4 PM PST Saturday
     for West Entrance U.S. Waters Strait Of Juan De Fuca.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.weather.gov/seattle/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.