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Area forecast discussion
National Weather Service Medford or
403 am PST Thu Jan 19 2017 upper level trough will shift through the area
today. This will keep showers going across the area, but
precipitation will be much less than yesterday. Most of the
streams and creeks are on their way down compared to yesterday, so
the areal Flood Watch was cancelled earlier. Even so, there are
still some main Stem river flood issues to deal with this morning
as the Rogue River at Agness is currently in minor flood and a
Flood Warning is in effect. Coquille river at Coquille is expected
to reach very near flood stage (21.0 ft) later this afternoon and
a Flood Warning also remains in effect for that forecast point.
The South Fork of the Coquille is showing signs of leveling off
and may not reach flood stage. We currently have a warning out,
but this will be re-evaluated through the morning.

Meantime, winter weather advisories in the Cascades, Siskiyous
and in Siskiyou County are set to expire this morning with just
minor additional snow accumulations. However, the next storm is
taking shape over the Pacific and the frontal system associated
with it will arrive at the coast this evening, then push onshore
overnight and inland Friday. Once again, we expect another round
of heavy, wet snow in Siskiyou County, including Mount Shasta
city tonight into Friday. This system won't be quite as strong as
the last one in terms of moisture and wind, but it will be
healthy nonetheless. Expect extremely hazardous conditions to
develop again along Interstate 5 from Weed southward overnight
into Friday morning with visibility occasionally below 1/4 of a
mile at times due to heavy snow. We have issued a Winter Storm
Warning for this and specific snow amounts can be viewed at
wswmfr. Snow amounts elsewhere are generally sub-advisory levels,
but there could be a time overnight into Friday morning where it
snows hard enough to cause some travel problems on the Cascade
passes and over Siskiyou Summit.

The pressure gradients associated with this system peak near -5.5
mb mfr-rdd and 700 mb winds peak at 45-55 kt late tonight. This
should bring advisory winds at least to the Shasta Valley and east
side late tonight into Friday morning and it should also get
breezy in the southern end of the Rogue Valley near Ashland. Will
let the day shift take another look at the guidance to see if any
advisories are necessary.

Onshore flow and additional short wave activity will keep a
showery pattern going Friday night into Saturday, but this should
be a least in a relative sense. Steadiest
precipitation...or coverage of showers...should be greatest in
south-central and western Siskiyou County and along the SW Oregon
coast. A few to several more inches of snow may accumulate in the
Shasta region and in the mountains. -Spilde

Extended forecast from Wednesday afternoon's discussion...Saturday
through Wednesday. Yet another strong frontal system will affect
our area over the weekend. This storm may be the strongest in the
sequence in terms of winds, as models all show deepening low
pressure recurving along the pacnw coast Saturday night into
Sunday. There are differences between the models regarding timing,
strength, and track of this low pressure, all of which would have
a big impact on the weather we ultimately experience.
Nevertheless, all are impressive enough to warrant keeping an eye
on this storm.

Snow levels will be relatively low with this storm, and dynamics may
be quite high, thus the biggest impacts are expected to be from snow
and wind. Snow is expected to be heaviest over the norcal mountains,
especially around Mt. Shasta city, where more than a foot could
easily fall. Strong winds will affect the usual spots (waters,
coast, east side, Shasta valley), but we may also get winds down
into the west side valleys Sunday morning.

This is not to say rain won't be an issue, because it will be heavy
along the South Coast and adjacent mountains. However, low snow
levels should lock much of this liquid up in the mountains, and quantitative precipitation forecast
amounts at the coast are not all that unusual for a winter storm.

Showers may linger into early next week, and some models hint at
another wave of low pressure forming in conjunction with the
departing upper wave Monday night, but confidence with that is low.
Beyond this, a ridge is expected to build, which should give US a
much needed break from the inclement weather. -Wright


Aviation...19/06z taf cycle...showers and unstable conditions will
brings rounds of MVFR conditions to most terminals tonight. Snow is
possible in Klamath Falls and will reduce visibility there. Winds
are diminishing in general, but they remain gusty east of the
Cascades, and turbulence potential is higher there. The worst
conditions continue to be in The Mount Shasta city area where snow
and low ceilings/visibility will continue overnight. Additionally,
mountain obscuration will be widepsread through the night.
Conditions generally increase tomorrow with VFR conditions
expected in most areas by the afternoon.


Marine...updated 900 PM PST Wednesday 18 January 2017...winds and
seas have diminished with winds dropping below Small Craft Advisory
and seas now dropping to Small Craft Advisory. Winds will be
relatively light Thursday, but the next front will bring another
period of gale to occasionally storm force winds and very steep seas
Thursday night into Friday morning. All major models are suggesting
gales now, and confidence has grown with this upcoming gale event.
Behind this front, long period extremely high west swell of 25 to 30
feet is expected late Friday into Saturday. Confidence is high for
this as this is the third day in a row that models have shown this
height range of seas.

Models are suggesting a period of high pressure and lower winds and
seas by the middle of next week.


Mfr watches/warnings/advisories...
or...Winter Weather Advisory until 4 am PST early this morning for
Winter Weather Advisory until 10 am PST this morning for

California...Winter Storm Warning from 10 PM this evening to 4 PM PST Friday
for caz080>083.
Winter Weather Advisory until 10 am PST this morning for
Winter Weather Advisory until 10 am PST this morning for caz080.
Winter Weather Advisory until 4 am PST early this morning for

Pacific coastal waters...hazardous seas warning from 4 am Friday to
4 am PST Sunday for pzz350-356-370-376.
Gale Warning from 4 PM this afternoon to 4 am PST Friday for
Small Craft Advisory for hazardous seas until 4 am PST Friday

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