High Wind in California, January 5, 2019

Area Forecast Discussion
National Weather Service Medford OR
900 PM PST Fri Jan 4 2019

.DISCUSSION...Please pay attention to warnings and advisories in
effect through tomorrow - we are expecting a significant wind
storm over our area!

The latest model guidance remains consistent with previous runs
in showing strong low pressure currently around 500 miles
southwest of us moving north along the CA/OR coast tomorrow and
bringing strong winds to virtually all of our forecast area. Very
tight surface pressure gradients as the low passes tomorrow as
well as strong winds just above the surface have combined to
produce some pretty impressive strong wind signals. For example,
statistical guidance (MOS) shows peak winds of around 35 mph with
gusts up to 45 mph tomorrow afternoon at the Medford airport. It
has been a long time since it has shown values that high.
Furthermore, model soundings over Medford show winds of 55-60 mph
getting to within around 1000 feet of the ground, and these strong
winds are all aligned from the southeast, which is exactly what
is needed for damaging winds around Ashland and strong winds
spreading into the rest of the Rogue Valley. Without inundating
readers with any more data, similar signals are evident for the
remainder of our area as well.

Winds are already gusty over the mountains and Shasta Valley, and
they will increase as the low approaches tonight. Elsewhere,
winds will develop suddenly tomorrow, and peak just as the low
pressure passes and for a few hours thereafter. This puts the
development of winds around mid to late morning with the peak of
the winds in the afternoon to early evening in most locations.

While wind is the most widespread impact from this storm, a more
acute, but still significant impact, will be the snow, especially
around Mt. Shasta. Guidance continues to show a lot of
precipitation around the city along with significant cooling via
dynamics and entrainment due to intense precipitation rates, the
result be very heavy snow. Some of this will likely melt since
it's coming during the day, but there will probably be some
impressive snowfall rates at times, and this should easily
overcome any melting.

To reiterate: One of the strongest and most dynamic storms of the
season, so far, is expected tomorrow. Strong winds will affect
the vast majority of our area, and heavy snow will affect travel
through the Mt. Shasta area. Please prepare and plan accordingly.
No updates are needed this evening. -Wright

&&

.MARINE...Updated 715 PM PST Friday, 4 January 2019...Widespread
steep and hazardous seas will continue through the weekend. Buoy 27
is showing largely similar conditions as to what is forecast, but
there are brief periods where 20 foot waves are being observed. Have
not made any changes to the forecast, but thought it was worth
noting.

Otherwise, a strong low pressure will push toward the coast early
Saturday morning, then move northward and push inland north of Cape
Blanco late Saturday afternoon. Strong winds will accompany this low
with south to southeast gales expected ahead of it through Saturday
morning. If the low continues to strengthen, there could be a storm
force gust here or there as well.

A rapid wind shift will occur Saturday afternoon, and westerly gales
will continue into Saturday evening. Seas will become very steep and
chaotic in response to these winds. Another, slightly weaker system,
will follow quickly Sunday morning. This low will move into northern
California, so the strongest winds will likely be south of Cape
Blanco. However, seas will be very steep and hazardous for all areas
through Sunday so have extended the Gale Warning through Sunday
night to cover this.

More frontal systems are expected through early next week with
periods of gales and very heavy steep seas likely. Conditions are
not expected to improve until frontal activity slows down late next
week. -Schaaf/BR-y

&&

.PREV DISCUSSION... /Issued 353 PM PST Fri Jan 4 2019/

Updated aviation discussion.

DISCUSSION...Two storms will impact the region through the weekend.
The main impact from both of these events will be strong winds and
the potential for heavy snow in the mountains of western Siksyou
county and most of south and eastern Siksyou County including Mount
Shasta. The details on each will follow below.

The latest satellite image shows storm number one already taking
shape near 37N and 134W. The general consensus is for the storm to
move northeast and reach southwest Oregon by Saturday morning. At
the same time the upper trough with this storm will become
negatively tilted as it approaches southwest Oregon with a deepening
surface low. Winds will increase early Saturday morning, especially
in the Shasta Valley with moderate to strong winds expected to cover
most of the forecast area mid to late Saturday morning through
Saturday evening. Right now, winds will be be strongest along the
coast, Shasta Valley, Cascades and Siskiyous, the higher terrain
east of the Cascades and portions of the Rogue Valley. The strongest
winds in the Rogue Valley will be down near Ashland, but there's,
enough evidence to suggest strong winds are possible in Medford
proper. In fact the Medford to Redding gradient is peaking out
around 9.5 mb Saturday afternoon.

Along the coast, strong winds are expected to affect the south coast
first from about Cape Blanco south, then the north coast will get
into the action Saturday afternoon. The models are showing the North
Bend to Arcata gradient over 13 mb by late Saturday afternoon and
early evening.

Along and east of the Cascades 700mb winds are expected to be in the
60-70 kt range, therefore the potential for moderate to strong winds
exist of the entire area. For details on all of the winds, please
NPWMFR for more details.

Another significant impact with storm number one is the potential
for heavy snow in the Mount Shasta region. Right now, it appears
that precipitation will begin Saturday morning in Siskiyou County,
then a period of moderate/heavy precipitation is expected late
Saturday morning through Saturday evening as upslope flow is
maximized by the mid-level 60-70kt winds. The winter storm watch has
been upgraded to a winter storm warning for elevations above 3000
feet for 6-10 inches of heavy, wet snow for western and southern
Siskiyou County. Some of the higher elevations above 4000 feet could
see more than a foot of new snow. Confidence in snow impacting
Interstate 5 near Mount Shasta City on Saturday is high, but
confidence in the snow level is a little less certain. This will be
driven mainly by precipitation rates. If the precipitation is heavy
enough, it could drag the snow level all the way down to Dunsmuir at
times. Model guidance, however, is unanimously keeping the snow
level 3000 feet and above. Please refer to the WSWMFR product for
more details.

We are also expecting snow over the Cascades and higher passes,
including Siskiyou Summit Saturday afternoon through Saturday night.
Snowfall amounts are expected to be less in these areas. However
could not rule out brief blizzard conditions Saturday evening due to
strong winds and any snow already on the ground and/or falling
mainly above 5500 feet. The details on this are also found at
NPWMFR.

Storm number two will be right on the heals of the first Sunday
afternoon through Sunday night. Unlike the first one, this low is
not as strong and is tracking further south. The details on this
could change, but should the models remain consistent, will also
bring bring another round of moderate to strong winds to the south
coast, Shasta Valley, east of the Cascades and possibly the Rogue
Valley.

Moderate to heavy snow for the Mount Shasta region looks more
certain Sunday afternoon through Sunday evening. Moderate to heavy
snow is also possible in the Cascades around Crater Lake, Diamond
Lake and northern highway 97 near Chemult. Additional wind and
winter weather headlines are likely with storm number two.
-Petrucelli

The weather pattern remains active through the extended period,
though a relative break in precipitation is expected Monday. Deep
low pressure over the offshore waters will slowly approach the coast
late Monday into Wednesday. Though winds from this low shouldn't be
as strong as the Saturday system (low is weakening gradually as it
moves eastward), there will be an extended period with the potential
for gusty winds in areas like the Shasta Valley, areas east of the
Cascades, and the Rogue Valley. Precipitation during this time will
be focused over the coast and Northern California again. Snow levels
will be higher during this period compared to the Saturday and
Sunday storms, and they'll be around 5000 feet. The heaviest
precipitation will likely be Wednesday. Drier conditions are
expected Thursday and Friday and into the weekend. -NSK

AVIATION...For the 05/00Z TAFs...VFR conditions prevail for the
majority of the area. A strong low pressure will approach early
Saturday. Winds will increase ahead of this front and this, combined
with continued high level cloud cover, should preclude any fog
development tonight into Saturday morning. However, given the time
of year and continued high moisture content in the low levels, there
is a small chance for a period of low ceilings and/or fog to form in
the Rogue, Illinois, and Umpqua Basins tonight. Strong winds aloft
will accompany the approaching system and wind shear will be a
concern for all sites west of the Cascades by early Saturday
morning. Strong winds will begin to surface at KRBG, KMFR, and KLMT,
among other areas, later Saturday morning. Expect widespread
significant turbulence through the forecast area Saturday.

One other note of significance...the lowest ceilings and poorest
visibility will likely be focused in the Mount Shasta City area
where heavy snow is expected Saturday. BR-y/Keene

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning from 7 AM to 10 PM PST Saturday for
     ORZ030-031.
     Wind Advisory from 10 AM to 10 PM PST Saturday for ORZ029>031.
     High Wind Warning from 7 AM to 10 PM PST Saturday for
     ORZ027-028.
     High Wind Warning from 10 AM to 7 PM PST Saturday for ORZ022.
     Wind Advisory from 10 AM to 7 PM PST Saturday for ORZ023>026.
     High Wind Warning from 1 PM to 10 PM PST Saturday for ORZ021.
     High Wind Warning from 10 AM to 7 PM PST Saturday for ORZ026.

CA...High Wind Warning from 7 AM to 10 PM PST Saturday for CAZ085.
     Wind Advisory from 10 AM to 10 PM PST Saturday for CAZ084-085.
     Wind Advisory from 10 AM to 7 PM PST Saturday for CAZ080.
     Winter Storm Warning from 11 AM to 11 PM PST Saturday above 3000
     feet in the for CAZ080.
     Winter Storm Warning from 11 AM to 11 PM PST Saturday above 3000
     feet in the for CAZ082-083.
     High Wind Warning from 4 AM to 10 PM PST Saturday for CAZ081.

Pacific Coastal Waters...Gale Warning from 7 AM Saturday to 4 AM PST Monday for
     PZZ350-356-370-376.
     Hazardous Seas Warning until 7 AM PST Saturday for
     PZZ350-356-370-376.