High Surf in Oregon, January 18, 2018

Area Forecast Discussion
National Weather Service Medford OR
850 PM PST Wed Jan 17 2018

.UPDATE...Satellite shows the cold front marching inland.
Associated precipitation has started in the Umpqua Basin and along
the coast. The next few hours will likely see the heaviest
precipitation for the coast... Brookings received close to half an
inch in the last hour, and will probably see another half inch
before midnight. Precipitation will spread south of the Umpqua
Divide later tonight. Strong southeast winds continue in the
Rogue Valley, which will give a slight delay to precipitation in
Medford... possibly postponing precipitation until a few hours
after midnight. Strong south winds are starting to come down in
the Shasta Valley, and should continue gradually diminishing
tonight into tomorrow morning. Winds remain strong east of the
Cascades, with gusts to 40 mph still being recorded at Summer
Lake. East Side winds probably won't start diminishing until early
tomorrow morning.

On another note, today's high here at the Rogue Valley airport
was 68, breaking the previous record high of 65. At the time of
this writing, it's still a balmy 60 degrees. Roseburg reached 71,
Klamath Falls reached 57, Montague hit 61, and North Bend hit 67,
all breaking records. Tomorrow won't be nearly as warm... steady
precipitation across the CWA, combined with the cold pool moving
in behind the front will probably bring cool conditions in the
afternoon, and most places will likely hit the daily max
temperature in the morning. Snow levels will drop to around 4500
feet in the Cascades and westward tomorrow afternoon, which will
bring travel impacts. A winter weather advisory remains in effect
for parts of the Oregon Cascades, including Highway 140...and for
parts of western Siskiyou County. For more information, see
WSWMFR.

Friday will be colder still, and a showery pattern will prevail
with snow levels 2500 to 3000 feet. Sunday, another wet system
will move in, bringing another round of elevated winds and snow
levels probably around 3000 to 4000 feet during the heaviest
precipitation. Will continue to narrow down that range in the
coming forecast cycles. No updates to the forecast were made this
evening, so previous discussion for more information. -MSC

&&

.AVIATION...18/00Z TAF CYCLE...Wind speed shear will be the main
concern for the westside terminals into tonight. The timing of when
wind speed shear will end at North Bend, Roseburg and Medford could
end sooner than whats in the TAF, but confidence was not high enough
to shorten the end time. In addition moderate turbulence is also
possible. The TAF at Roseburg shows MVFR CIGS overnight into
Thursday with widespread terrain obscurations and periods of rain,
including Roseburg. It's possible CIGS could remain VFR, but for now
left the lower conditions in. Later shifts will need to take another
look at this. Elsewhere, VFR cigs are expected to prevail through
the TAF period. Freezing levels will lower to around 5500 feet by
Thursday morning. -Petrucelli

&&

.MARINE...Updated 830 PM PST Wednesday 17 Jan 2018...Southwest winds
behind a cold front will remain gusty overnight. A very high and
dangerous westerly swell will follow late tonight into Thursday.
Model guidance has been steadfast, showing the swell peaking at
around 28 feet Thursday morning. Expect a 24-36 hour period of
extremely rough surf, making bar crossings very dangerous. Seas will
remain elevated with weaker systems moving through Thursday night
into Friday. A High Surf Advisory will likely be in effect once the
warning ends early Friday. Swell dominated seas diminish slightly
Saturday but another strong front will move through with seas
becoming very high again late Saturday night into Sunday. High
pressure will build Monday with improving conditions between systems
into Tuesday morning. -JRS/DW

&&

.PREV DISCUSSION... /Issued 354 PM PST Wed Jan 17 2018/

SHORT TERM...The cold front is moving inland this afternoon.
Gusty winds will continue in the Shasta Valley and at the higher
terrain overnight. Satellite imagery shows a wave is trying to
form on the front and this will slow down the eastward movement.
South winds in the Shasta Valley and south end of Jackson County are
expected to peak late this evening, but areas east of the Cascades
may not see peak winds until after midnight tonight. By late
Thursday morning measurable precipitation is expected to spread
into the Klamath Basin then into the Goose Lake Basin by early
Thursday afternoon.

The front will also bring snow to the mountains as early as late
tonight. Snow levels will be quite high early in the day at or
above 6000 feet so travel across the mountain passes should not
be a problem early in the day. Cold air behind the front is
expected to bring the snow levels down to around 4500 feet around
noon and we could start to see snow at the mountain passes by
early afternoon. By Thursday evening, snow levels lower to around
3000 feet and snow accumulations across the major passes are
likely Thursday night into Friday. Snow accumulation around 3 to 4
inches is possible across the Cascade Passes and around 1 to 2
inches over the Siskiyou Pass Thursday night. Sexton Pass could
see mixed precipitation late Thursday night but snow levels are
not expected to lower to near that pass level until Friday night.

On Friday a broad upper level trough will settle over the Pacific
NW with widespread snow levels in the 2000-2500 foot range. In
spite of a ridge building into the area, there will still be
enough moisture and instability to generate scattered showers
across the area. The ridge will be short lived and is expected to
move out of the area by Sunday. /FB

LONG TERM...Sunday through Wednesday
The general consensus is the pattern will remain fairly active
during this time period. There will be some breaks in the action,
but not for an extended period of time. There is now better
agreement with the timing of the front on Sunday. There are still
some differences with the timing of the front, but overall the
models are in much better agreement compared to yesterday. The
ECMWF is still a bit slower with the arrival of the front, but
suspect they will come into better agreement in time.

The main impact on Sunday will be the winds, especially in the
Shasta Valley and eastside. These areas have a chance to reach at
least advisory levels with high wind warning criteria possible in
the south end of the Shasta Valley near Weed and higher elevations
like Summer Lake east of the Cascades. Also the south end of the
Rogue Valley from around Phoenix to Ashland could reach advisory
criteria. Right now, winds in the above mentioned areas are expected
to be strongest from late Sunday morning through Sunday evening, but
the timing could change, so watch for updates. Gusty winds are also
expected along the coast and headlands Sunday morning, but should
remain below warning criteria.

The highest precip amounts on Sunday will be in the usual areas. The
coast and coastal mountains and the Cascades. The front is expected
to move onshore Sunday evening, therefore snow levels during the day
will end up higher. They will start out around 3500 feet Sunday
morning and could even rise to around 4500 feet Sunday afternoon.
This is when the bulk of the precipitation will come in. So road
snow concerns look like they will be confined to the highway 140
near Lake of the Woods, Diamond Lake, Crater Lake and Mount Ashland
Ski area. Siksyou Summit and Mount Shasta region could pick up
couple of inches at best Sunday morning with little or nothing Sunday
afternoon as snow levels come up. Keep in mind the details on this
could change.

The front will move through the area Sunday night. Winds will
decrease over most locations. Snow levels will come down, but by
then precipitation will also be on the decrease which should limit
the amount of accumulating snow.

It still looks like we'll catch a relative break in the action
Monday into Tuesday. Moist northwest flow on Monday will result in
showers mainly confined to the coast. Weak shortwave ridging ahead
of the next front will bring dry conditions for most of Tuesday.
Winds will increase again Tuesday afternoon along the coast as
another strong front approaches with precipitation to follow for
most locations Tuesday evening and night. -Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning until 4 AM PST Thursday for ORZ030-031.
     Wind Advisory until 7 AM PST Thursday for ORZ030-031.
     High Surf Warning until 4 AM PST Friday for ORZ021-022.
     Winter Weather Advisory from 10 AM Thursday to 10 AM PST Friday
     for ORZ027-028.
     Wind Advisory until 10 PM PST this evening for ORZ026.

CA...Winter Weather Advisory from 10 AM Thursday to 10 AM PST Friday
     for CAZ080.
     High Wind Warning until 4 AM PST Thursday for CAZ081.
     Wind Advisory until 4 AM PST Thursday for CAZ081.
     Wind Advisory until 4 AM PST Thursday for CAZ085.

Pacific Coastal Waters...Hazardous Seas Warning until 4 AM PST Saturday for
     PZZ350-356-370-376.

MSC/FJB/MAP/DW