High Wind in Washington, February 7, 2017

Area Forecast Discussion
National Weather Service Seattle WA
305 AM PST Tue Feb 7 2017

.SYNOPSIS...A mostly dry and cool day today as high pressure over
British Columbia and low pressure moving to the south brings
offshore flow. A strong warm front will lift northward through the
area on Wednesday and Thursday, bringing rainy and windy weather,
along with heavy snow in the Cascades. A cold front will then sweep
by on Friday with additional showers. A strong upper ridge should
then build into the Pacific Northwest this weekend bringing a
return to dry conditions.

&&

.SHORT TERM...Current radar is mostly clear...certainly a change
from the past 24-36 hours...and dramatically different from what is
expected 24-36 hours from now. Still...definitely worthwhile to bask
in this minor break afforded to Western Washington thanks to a
pretty minor upper level ridge which will keep conditions dry today
and into early Wednesday morning. Speaking of dry conditions...have
opted to cancel inherited Winter Weather Advisory due
to...well...dry conditions.

Like all such things...it comes to an end far too soon. Late
Wednesday morning to Wednesday afternoon shows a warm front making
its way up from the south and bringing with it an impressive amount
of moisture. The good news is that once this front passes the area
will see a jump in daytime highs...with temps Thursday afternoon
approaching 50 degrees in the lowlands. The bad news is these warmer
temps are going to be served up with an all you can eat buffet of
rain to go with it. This blob of moisture lingers over much of the
area into Thursday...resulting in moderate to heavy rainfall rates
over portions of the area. This could result in some hydro issues
which will be touched upon in the .HYDROLOGY section below. Activity
looks to start to taper off Thursday night but...well...best to save
that for the Long Term discussion.

The Cascades certainly will not be left out of the quote fun
unquote. Snow levels will be slow to rise at the onset of the
Wednesday system...given that it likely will not impact that area
until the evening. Snow amounts for the central and southern
portions of the Cascades look to fall easily into Winter Storm
criteria at this time...however...in terms of the forecast...the
timing of the event looks to fall into the fourth period and as
such...will abdicate any headline issuance to dayshift and allow an
additional model run or two to shore up confidence.  SMR

.LONG TERM...So that tapering off for Thursday night...not so
much...as a frontal system and associated upper level trough looks
to enter the area early Friday morning and keep the precip going
into Friday night.

It is not all doom and gloom though...as things start to taper off
for real this time Saturday morning in advance of an upper level
ridge pushing into the region. That ridge looks to stay in place and
bring dry conditions for the remainder of Saturday...Sunday and even
possibly into the middle of next week.  SMR

&&

.AVIATION...Snow showers will mainly affect the northern portion of
the CWA early this morning. Otherwise, the air mass will dry out
today with N/NE offshore flow. There is patchy fog in the south
sound but should see VFR conditions across the board this afternoon.
The flow aloft is westerly. Weak upper level ridging and offshore
flow will continue tonight. 33

KSEA...Brief MVFR ceilings are possible this morning then low clouds
scattering out in the afternoon. Light/variable winds becoming N/NE
by 18z. 33

&&

.MARINE...Offshore flow will prevail today with high pressure
over interior British Columbia. A strong warm front may bring gales
to the waters on Wednesday. Strong onshore flow will follow Thursday
and Friday. High pressure will build inland on Saturday for a period
of lighter winds. 33

&&

.HYDROLOGY...From previous discussion...No river flooding expected
through Wednesday. A warm, wet Pacific frontal system will spread
rain across the area late Wednesday through Friday. At this point
around 3 inches of rain may fall in the 30 hours from Wednesday
morning through Thursday afternoon, with possibly as much as 5
inches over the Olympics. S-SW winds at 850 MB will reach 45-55 KT
over the Olympics resulting in a decently strong orographic
enhancement to the rainfall there. Rivers will rise and there may be
some potential for one or more to reach flood stage Thursday or
Friday. Melting snow in the lower elevations leading up to the storm
might also contribute to putting moisture into the ground and
thereby slightly increasing the runoff efficiency.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory 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 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 4 PM PST Wednesday for Central U.S.
     Waters Strait Of Juan De Fuca-Coastal Waters From Cape
     Flattery To James Island Out 10 Nm-Northern Inland Waters
     Including The San Juan Islands-West Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory until 3 AM PST early this morning for Puget
     Sound and Hood Canal.

&&

www.weather.gov/seattle

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