High Wind in Oregon, January 25, 2018

Area Forecast Discussion
National Weather Service Medford OR
846 PM PST Wed Jan 24 2018

.DISCUSSION...Updates were already made this evening, and we're
not expected to need any more (save for cleaning up headlines as
they expire). A cold front is moving across the east side this
evening, and while it is now literally flying under the radar for
the most part, satellite interpretation as well as wind
observations and pressure tendencies indicate it's probably right
along the Lake/Klamath and Modoc/Siskiyou county lines. We're in a
break from the steady precipitation behind the front, but there
are still plenty of showers around, especially in the mountains.

This break will be short-lived as satellite shows significant
convective cells already lining up just off the coast. Model
guidance shows the upper trough responsible for these showers
arriving at the coast around dawn tomorrow and then moving across
the northern part of our area through the morning. At the same
time, a surface low moves across the northern waters and into the
coast around right around Reedsport. As a result, another
significant uptick in precipitation is expected late tonight
through tomorrow morning, especially across the west side and in
the mountains. There will also be another surge in wind. Luckily,
the surface low isn't deepening, otherwise, such a track could be
a big wind producer.

Snow levels have fallen to around 3000 feet across the west side
this evening, and models show them dropping to around 1500-2000
feet by tomorrow. This will mean moderate to heavy snow in the
mountains re-developing later tonight and tomorrow morning, and
this will likely impact travel even over the lower passes along
I-5 between Grants Pass and Roseburg. We have winter storm
warnings and advisories out that cover this well.

Winds have died down somewhat this evening, and this allowed me
to lower the high wind warnings we had going. However, as the
upper trough/surface low moves across our area tomorrow, there is
a noticeable surge of wind again, especially across portions of
the east side. Guidance indicates winds likely won't reach high
wind warning criteria, so we've covered that with a wind advisory
that spans tonight and tomorrow. Winds in the Shasta Valley are a
little more questionable, but there is enough potential in the
Weed area to be worthy of an advisory, and one was issued earlier
this evening. -Wright

&&

.AVIATION...25/00Z TAF CYCLE...Though periods of VFR conditions
will occur at terminals, expect generally widespread MVFR
conditions with gusty south winds as showers continue across the
area. The cold core upper low shifting into the PacNW will bring a
slight chance of lightning to the coast... a few lightning
strikes have already been observed offshore. Freezing levels
across the area will drop around 2000 feet tonight. Conditions
will likely lower to IFR at times in heavy precipitation.
Widespread terrain obscuration is also expected. -MSC

&&

.PREV DISCUSSION... /Issued 251 PM PST Wed Jan 24 2018/

SHORT TERM...A strong front which moved into the area today has
moved east of the Cascades and will shift east of the area
tonight. This front has brought significant snow to the mountains.
Precipitation will diminish by late this evening. Winds will
remain strong and gusty east of the Cascades, with strongest winds
in the Summer Lake area and over the higher mountains in Lake and
Modoc county. Winds will decrease late this evening and tonight
for these areas.

There will be little break though in the active pattern though. An
upper trough will nudge into the region tonight bringing a cold
and showery air mass. A low pressure center offshore near 43.5N
and 134.5W will move inside of 130W tonight and near the central
oregon coast early Thursday morning. This low will bring strong
winds aloft and will send an front inland that will enhance
precipitation across the area. Expect moderate to locally heavy
showers to develop, mainly from the Cascades west by the early to
mid morning hours on Thursday. Some moderate showers are also
expected to spread east of the Cascades by late Thursday morning.

As snow levels are expected to lower down to 1500 to 2500 feet
tonight and early Thursday morning, expect areas west of the
Cascades to see light to moderate snow accumulations as this
front brings showers into the area. Lower valley floors below
1500 feet are not expected to see significant accumulating snow.
The one area of concern is the Illinois Valley which may see some
light snow below 1500 feet Thursday morning. For the higher
terrain, heavy snow accumulations are expected for the Kalmiopsis
Wilderness area, western Siskiyou mountains and for higher terrain
in the Mount Shasta area. Additionally, passes in the Southern
Oregon Cascades and east into northern Klamath county are also
expected to see moderate snow on Thursday.

Due to the convective nature of this system, expect snow levels
and accumulations to vary, especially in heavier shower activity.
Any heavy shower bands may bring snow levels locally lower. Have
kept the lowest snow levels of around 1500 ft in the Josephine
county area, including the Illinois Valley and to Sexton Summit,
where shower activity is  expected to be stronger. Elsewhere have
leaned towards snow levels of 2000 feet rising to 2500 feet
during the afternoon and evening Thursday. Will need to monitor
snow levels as precipitation moves into the area.

Winds are also a concern with this front. Strong and gusty winds
of 35 to 45 mph are likely for the coast as the low nears the
central Oregon coast late tonight and early Thursday morning.
Inland, expect some strong gusty winds in the southern Shasta
Valley and east of the Cascades. For inland areas, strongest winds
are expected east of the Cascades near Summer Lake where southwest
winds may gust in the 40 to 50 mph range Thursday morning. Models
show variability on the exact strength of these winds Thursday
morning. So will need to monitor this with the next set of model
runs.

Widespread showers will continue into Thursday evening, then is
expected to decrease as the upper trough shifts eastward. Will
continue to see lingering light showers though Thursday night and
Friday, mainly along the coast and into Douglas county due to a
weak front moving inland north of the area.

LONG TERM...Friday evening through Wednesday. The active pattern
will continue. The EC and GFS have stayed in decent agreement over
the last few model runs. A low will drift into the marine waters
Friday evening. This low will push a warm front through the Medford
CWA, bringing a substantial round of precipitation during the day
Saturday, along with some gusty south or southwest winds in the
usual areas... the coast, the Shasta Valley, and the East Side.
Expect a healthy amount of precip at the coast, though nothing
absurd for this time of year. Heaviest amounts are forecast south of
Cape Blanco. Brookings will probably get 2 to 3 inches in a 24 hour
period... while Coos Bay will get closer to an inch.

Warm air advection will cause rising snow levels throughout the day
Saturday. Expect snow levels around 2500 feet when precipitation
begins Friday night... then reaching 6000 to 7000 feet by Saturday
night. Confidence in details will increase as we get more hi-res
guidance, but right now, it looks like Crater Lake will see around a
foot of snow Friday night into Saturday evening... Lake of the Woods
will get around 6 inches ... and Mount Shasta City and Klamath Falls
can both expect an inch or two in that time frame. Travel impacts in
the lower passes should mostly end by Saturday afternoon, as snow
levels rise. We will continue to monitor this time period and refine
details.

A ridge will build in Sunday, drying out conditions save for a few
lingering showers. The forecast gets more complex Monday... another
stream of moisture with subtropical origins will impact the Pacific
Northwest. Right now, it looks like most impacts will be felt in
northern Oregon and southern Washington, so kept PoPs as mostly
chance in southern Oregon/ northern Cal for now... this feature will
need to be monitored. If the track shifts south, there could be
river flooding concerns. In any case, a cold front will sweep
through the region Tuesday bringing a quick shot of precipitation.
Wednesday onward, models lean towards general ridging and dryer than
normal weather. -MSC

MARINE...Updated 230 PM PST Wednesday 24 Jan 2018...A hazardous
seas warning is in effect through Thursday night. The main change
to the forecast was to upgrade the portion of the hazardous seas
warning in the southern waters beyond 10 nm to a gale warning. The
other change was to shorten the duration of the hazardous seas
warning with a slight improvement to advisory conditions during
Friday.

Gales will accompany the next front late tonight into Thursday
morning. A few rumbles of thunder have occurred today, and the
slight threat for isolated thunderstorms will continue through
Thursday afternoon. Very steep seas will build tonight
through Thursday and become very high. Another couple of very strong
fronts are expected Friday night into Saturday and on Saturday night
with the threat of gales increasing with the possibility of storm
force winds with the coastal jet beyond 10 nm north of Nesika Beach.
With this front on Friday night, seas are expected to become very
steep and very high again, and could reach 20 feet. -Schaaf

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 10 PM PST this evening for
     ORZ029-030.
     Winter Weather Advisory from 7 AM to 10 PM PST Thursday for
     ORZ027>030.
     Wind Advisory until 1 PM PST Thursday for ORZ030-031.
     Winter Storm Warning until 10 PM PST this evening for
     ORZ029-030.
     Winter Weather Advisory from 1 AM to 10 PM PST Thursday above
     1500 feet in the for ORZ024.
     Winter Storm Warning from 1 AM to 10 PM PST Thursday above 2500
     feet in the for ORZ024.
     Winter Weather Advisory from 7 AM to 10 PM PST Thursday above
     2500 feet in the for ORZ023.
     Winter Storm Warning until 10 PM PST this evening above 5000
     feet in the for ORZ027-028.
     Winter Weather Advisory from 7 AM to 10 PM PST Thursday above
     2000 feet in the for ORZ025-026.

CA...Wind Advisory until 1 PM PST Thursday for CAZ085.
     Winter Weather Advisory until 10 PM PST Thursday below 4000 feet
     in the for CAZ082.
     Winter Storm Warning until 10 PM PST Thursday above 4000 feet in
     the for CAZ082.
     Winter Weather Advisory until 10 PM PST Thursday above 2000 feet
     in the for CAZ080.
     Winter Storm Warning until 10 PM PST Thursday above 3500 feet in
     the for CAZ080.
     Wind Advisory from 4 AM to 10 AM PST Thursday for CAZ081.
     Winter Weather Advisory until 10 PM PST Thursday for CAZ083.
     Winter Storm Warning until 10 PM PST Thursday for CAZ083.

Pacific Coastal Waters...Gale Warning until 8 AM PST Thursday for
     PZZ350-356-370-376.
     Hazardous Seas Warning until 4 AM PST Friday for
     PZZ350-356-370-376.