High Surf in Oregon, January 21, 2017

Area Forecast Discussion
National Weather Service Medford OR
847 PM PST Fri Jan 20 2017

.SHORT TERM...A upper low is centered off the Washington coast
with an upper trough over the Pacific Northwest. Showers will
become widespread and increase in intensity along the coast and
into western and south central Siskiyou County tonight into
Saturday morning as a shortwave moves around the base of this
trough and over the area. This combined with snow levels lowering
to 3000 feet and locally down to 2500 feet will bring areas of
moderate snow to western Siskiyou county and in south central
Siskiyou county near the Mount Shasta area. A winter weather
advisory for snow has been added for these areas. Showers are
expected to briefly decrease in intensity and coverage during the
day on Saturday but this will be brief as a powerful storm is
forecast to move into the area Saturday evening through Sunday
afternoon.

Overall the forecast is on track with a very strong low moving
towards the area late Saturday and then shifting north as it
brings a strong front inland Saturday night through Sunday
afternoon. Models continue to show good agreement with this storm
tracking into the area from the southwest with the surface low
tracking along or just inside of 130 W as it deepens and moves
northward off the Oregon coast. This storm is expected to bring
strong winds along the coast and into the Shasta Valley and strong
winds area also possible in the Rogue Valley, over the higher
mountains and east of the Cascades. Winds may reach gusts of 80
mph along the coast and gust to 60 to 70 mph in the inland areas
affected. These winds will bring the potential for trees down and
power outages as well as dangerous travel conditions. Please see
the NPWMFR for details. Also of significant concern, heavy snow is
forecast across many areas in Siskiyou County and into the Warner
and other mountains in Modoc County. The heaviest snow is
forecast in the Mount Shasta area where 1 to 2 feet of snow
accumulation is expected and higher amounts on the mountain.
Moderate snow amounts are expected into the Shasta Valley in
Siskiyou County, in the valleys in Modoc county and into the
Siskiyous and Southern Oregon Cascades as well. Dangerous travel
conditions with snow packed or impassable roads and low visibility
are expected in the areas impacted by the heaviest snow. Travel
may also be hazardous due to slick and snow covered roads in the
areas impacted by moderate snow. Please see the WSWMFR for
details.

&&

.AVIATION...21/00Z TAF Cycle...CIGS will occasionally lower to MVFR
tonight as showers move across the area. MVFR coverage will increase
after sunset and is expected to become widespread late tonight and
toward daybreak on Saturday. Another front will move inland Saturday
morning, and will lead to gusty south winds at the coast and SE
winds up to 30 knots in the Shasta Valley and the Klamath Basin. The
front will also bring widespread MVFR cigs/vis to the Klamath Basin
and Siskiyou/Modoc Counties with occasional IFR conditions in
moderate snow. /FB

&&

.MARINE...Updated 300 PM PST Friday 20 January 2017...Very high and
very steep long period west swell will build seas to 24 to 28 feet
at 18 seconds overnight into Saturday morning. Winds, as a whole,
will be south to southwesterly at advisory level during the time
period. Another strong storm will deepen to sub-970 mb along 130
West and move northward Saturday night into Sunday. Confidence in
storm force winds is high as all models show 50-55kt BL southerly
flow across the waters with an occlusion Saturday night, so have
upgraded the storm watch to a storm warning. The storm force winds
will begin Saturday evening in SW Outer zone, then spread across
most of the waters overnight. Model guidance still indicates at
least gale force winds continuing into Sunday afternoon with
potential for storm force gusts, so have continued the storm warning
through early afternoon. Strong winds will gradually subside Monday,
but it will take a bit longer for the seas to come down - probably
Tuesday. -Spilde

&&

.PREV DISCUSSION... /Issued 316 PM PST Fri Jan 20 2017/

DISCUSSION...We'll have a relative break in the action tonight into
Saturday in terms of strong winds and heavy precipitation. An upper
low off the Washington coast will continue to bring a moist onshore
flow over our area. Showers this evening into Saturday will be
mainly focused along the south coast, coastal mountains and western
Siskiyou county, but were not expecting excess rainfall totals.

A strong storm will affect southern Oregon and northern California
Saturday night through at least Sunday afternoon. The models are in
pretty good agreement with a surface low deepening near or just
inside of 130 W Saturday night then moving north along 130 W on
Sunday. There seems to be general agreement that we'll see strong
winds over the waters, Shasta Valley, and east side. Some solutions
also show very strong winds along the coast and Shasta Valley. Given
the agreement in these aspects, the high wind watch has been
upgraded to a warning. Depending on the strength of the low, strong
winds may also develop in the Rogue Valley (Medford area) as well,
but confidence is much lower in that. Also the same applies to the
eastside, so we'll leave the watched up for now in these areas. See
NPWMFR for more details.

This storm is also likely to bring another round of heavy snow to
most of Siksyou County, including Mount Shasta City. Heavy snow is
expected to arrive Saturday night and continue into Sunday
afternoon. In fact snowfall rates could range between 1-2 inches per
hour Saturday night through Sunday morning. Could not rule out
moderate to heavy snow in the Siskiyous and southern oregon
Cascades, including I-5 near Siksyou Summit, Mount Ashland Ski
area, Highways 66 and 140 near Lake of the Woods. Confidence is high
most of Siksyou County will get the brunt of the snow and have
upgraded the winter storm watch to a warning. Also winter weather
advisories have been issued for portions of the Siskiyous, Cascades
and Modoc County. Please see WSWMFR for more details.

The upper and surface low will gradually move south Sunday night
with continued showers. However the worst of the weather in terms of
rain, snow and wind should be over with. -Petrucelli

LONG TERM...Monday through Thursday Night...The long term period
begins with showers after the aforementioned system from the short-
term forecast discussion. These showers are expected to be much
lighter, but models are prolonging the showers to continue with wrap
around moisture as the low is now forecast to weaken and dip
southward into central California. Confidence is still relatively
low on this scenario as models are sowing wide disagreements on how
close the low will come to the coast and where it will make
landfall, with the GFS and NAM being the more progressive solutions
moving the low quickly into Central California. However, have
blended the previous forecast with the ECMWF which has held more
constant in run to run solutions (and generally performs better in
the long-term anyway).

There will be a break from the more active weather beginning as
early as Tuesday, and things should dry out. The cool weather is
expected to remain as a ridge builds in. This dry pattern is
expected to continue through the rest of the week despite the ECMWF
and the Canadian models showing a dying front approaching the Oregon
coast by Wednesday night into Thursday. Have bumped up pops
slightly, as per the ECMWF; but still show the silent 10% chances
for the coast and coastal range.

The tricky part of the forecast regards the possibility for air
stagnation. Easterly winds are expected to be light across the
entirety of the forecast area after Tuesday, but this front could
help mixing just enough to prevent air quality problems. This dying
front will need to be monitored in

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Watch from late Saturday night through Sunday
     afternoon for ORZ029>031.
     High Wind Warning from 1 AM to 1 PM PST Sunday for ORZ021-022.
     High Surf Advisory until 10 PM PST this evening for ORZ021-022.
     High Surf Warning until 10 PM PST Saturday for ORZ021-022.
     Winter Weather Advisory from 4 PM Saturday to 4 PM PST Sunday
     for ORZ028.
     High Wind Watch from Saturday evening through Sunday afternoon
     for ORZ026.

CA...High Wind Watch from late Saturday night through Sunday
     afternoon for CAZ084-085.
     Winter Weather Advisory until 11 AM PST Saturday ABOVE 3000 FEET
     for for CAZ080.
     Winter Storm Warning from 4 PM Saturday to 4 PM PST Sunday ABOVE
     3000 FEET for for CAZ080.
     Winter Weather Advisory until 11 AM PST Saturday for CAZ082-083.
     Winter Storm Warning from 4 PM Saturday to 4 PM PST Sunday for
     CAZ082-083.
     High Wind Warning from 10 PM Saturday to 4 PM PST Sunday for
     CAZ081.
     Winter Weather Advisory from 4 PM Saturday to 4 PM PST Sunday
     for CAZ081.
     Winter Storm Warning from 4 PM Saturday to 4 PM PST Sunday for
     CAZ081.
     Winter Weather Advisory from 4 PM Saturday to 4 PM PST Sunday
     for CAZ085.
     Winter Storm Warning from 4 PM Saturday to 4 PM PST Sunday for
     CAZ085.

Pacific Coastal Waters...Storm Warning from 7 PM Saturday to 1 PM PST Sunday for
     PZZ350-356-370-376.
     Gale Warning from 7 PM Saturday to 10 PM PST Sunday for
     PZZ350-356.
     Hazardous Seas Warning until 7 PM PST Saturday for
     PZZ350-356-370-376.
     Gale Warning from 1 PM to 10 PM PST Sunday for PZZ370-376.

CC