Heavy Snow in California, January 19 to 20, 2017

Area Forecast Discussion
National Weather Service Medford OR
310 PM PST Thu Jan 19 2017

.DISCUSSION...Through Saturday Night...Not much is expected to
happen into early this evening. A few showers will linger around,
but that's it. Out next attention is the next storm that will
impact our area tonight through Friday afternoon. This storm is
not as strong as the last one in terms of wind and heavy rain, but
it will bring heavy wet snow to portions of northern California
with most of the emphasis in Siskiyou County. In fact Mount Shasta
could get hammered with heavy wet snow later tonight through
Friday morning due to a favorable upslope flow. Because of this
travel will be very hazardous and is strongly discouraged. Snow
will impact portions of Modoc County, but amounts are not expected
to be as much. Snow is expected to impact the Siskiyous and
southern Cascades resulting in snow covered roads, amounts will be
less, but still enough to create hazardous conditions. Please see
WSWMFR for details.

Gusty winds the Shasta Valley and along highway 31 between Paisley
and Summer Lake could reach advisory criteria. This is covered in
the winter weather product for the Shasta Valley and a wind
advisory has been issued for the Summer Lake area.

A relative break in the action is expected Friday night into
Saturday afternoon before the next storm arrives. -Petrucelli

Sunday and Monday...Another strong storm will affect southern
Oregon and northern California Sunday. All models show a strong
upper low moving to around 130W off the Washington coast during
the day Sunday. A frontal system will extend south from the low
along the PacNW coast, and then we may have low pressure develop
along the front and move north along the coast. I say may, because
the models are split on this detail and all have been alternating
back and forth between which is the strongest with the low for
several runs now. There seems to be general agreement that we'll
see strong winds over the waters, Shasta Valley, and east side,
along with heavy snow over much of Siskiyou county. Some solutions
also show very strong winds along the coast. Given the agreement
in these aspects, high wind and winter storm watches were issued
in the areas where confidence is highest. 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. The low then drops south along the coast Monday with
continued steady rain along the coast and possibly continued snow
in the Shasta area and showers elsewhere. The aspect of Monday
that bears watching is whether the low comes more over land, in
which case we'd have much more snow impacts in the mountains than
currently shown. -Wright

Tuesday through Thursday Night...Models are finally
showing a break from the more active weather shown in the earlier
periods. A few lingering showers may occur overnight Monday into
Tuesday morning, particularly for northern California, before
things dry out Tuesday evening. This dry pattern is expected to
continue through the rest of the extended, despite a weak front
approaching the coast on Wednesday and Thursday. Models indicate
that this front will dissipate before bringing any precipitation
to our coast.

The tricky part of the forecast regards the possibility for air
stagnation. Winds are expected to be light across the entirety of
the forecast area, but this front could help mixing just enough to
prevent air quality problems. That being said, mixing will start
out limited on Wednesday, so this pattern will need to be
monitored in the coming days. -Schaaf

&&

.AVIATION...19/18Z TAF Cycle...VFR conditions will continue
through this evening area-wide. Isolated snow showers may produce
brief MVFR conditions on the east side. Stratus and fog may
result in IFR conditions in the Umpqua basin late tonight, but an
incoming front will likely keep it unstable enough to prevent it
elsewhere. Rain will overspread the west side Friday morning with
light snow on the east side, all of which may reduce conditions to
MVFR. -Wright

&&

.MARINE...Updated 300 PM PST Thursday 19 January 2017...South
winds  will increase this afternoon and evening ahead of the next
front...reaching gales tonight then diminishing some Friday. High
and very steep seas are expected over much of the waters this
afternoon through the weekend. Increasing long period west swell
will build seas to a peak Friday night into Saturday morning of 25
to 30 feet. Another strong storm is likely Saturday night into
Sunday with storm force winds possible and high to very high seas
persisting into early next week. Confidence is low on timing and
location of storm force winds, and that is why the Storm Watch is
valid for 30 hours. With that said, most of the latest computer
models suggest a deep enough low in the vicinity of the waters
Saturday night into Sunday to warrant a Storm Watch. SK

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Watch from late Saturday night through Sunday
     afternoon for ORZ029>031.
     Winter Weather Advisory from 10 PM this evening to 4 PM PST
     Friday for ORZ031.
     Wind Advisory from 10 PM this evening to 1 PM PST Friday for
     ORZ031.
     High Surf Advisory until 4 PM PST Friday for ORZ021-022.
     High Wind Watch from late Saturday night through Sunday
     afternoon for ORZ021-022.
     Winter Weather Advisory from 10 PM this evening to 4 PM PST
     Friday for ORZ028.

CA...High Wind Watch from late Saturday night through Sunday
     afternoon for CAZ084-085.
     Winter Weather Advisory from 10 PM this evening to 4 PM PST
     Friday for CAZ085.
     Winter Storm Warning from 10 PM this evening to 4 PM PST Friday
     for CAZ080>083.
     Winter Storm Watch from Saturday afternoon through Sunday
     afternoon for CAZ080-082-083.
     Winter Weather Advisory from 10 PM this evening to 4 PM PST
     Friday for CAZ080-081-083.
     High Wind Watch from Saturday evening through Sunday morning for
     CAZ081.

Pacific Coastal Waters...Storm Watch from Saturday afternoon through
     Sunday evening for PZZ350-356-370-376.
     Hazardous Seas Warning until 9 PM PST this evening for
     PZZ350-356-370-376.
     Hazardous Seas Warning from 4 AM Friday to 10 PM PST Sunday for
     PZZ350-356.
     Gale Warning from 9 PM this evening to 4 AM PST Friday for
     PZZ350-356-370-376.
     Small Craft Advisory for hazardous seas until 4 AM PST Friday
     for PZZ350-356-370.
     Hazardous Seas Warning from 4 AM Friday to 4 PM PST Saturday for
     PZZ370-376.
     Small Craft Advisory for hazardous seas until 9 PM PST this
     evening for PZZ376.