High Wind in California, December 9 to 10, 2022

Area Forecast Discussion
National Weather Service Medford OR
243 PM PST Fri Dec 9 2022

.SHORT TERM...Tonight (12/9) through Saturday night
(12/10)...Radar is showing that precipitation is moving far enough
inland with a large hole over the Rogue Valley as potions of the
northern California. I imagine that the the rain will fill these
downsloping holes soon. In addition, winds are on the rise across
much of the area. This is all part of a winter storm that is
moving across the area tonight into Saturday. Most of the forecast
remains similar to what was inherited, and each of the expected impacts
will be discussed below.

WIND- Strong winds are are likely over the exposed areas along
the coast, mainly around and south of Cape Blanco. Guidance shows
pressure gradients between Arcata and North Bend are now around 12
mb which almost always results in high wind along the coast. A
High Wind Warming remains in effect for exposed areas above 1500
feet primarily from Cape Blanco south. Moderate to strong winds
are also expected in the Shasta Valley, with the strongest winds
near Weed. Meanwhile we could experience gusty southeast winds in
the Rogue Valley, especially from about Phoenix south to Ashland,
although Medford could also experience gusty southeast winds
through this evening. Additionally, expect gusty winds in portions
of the Umpqua Valley and higher terrain above 1500 feet in
Josephine and Douglas Counties. Have expanded the wind advisory to
include these areas. Moderate to strong winds are also likely
east of the Cascades with 700mb winds between 60-70 kts moving
over the Cascades later tonight, and peaking out between 75- 80
kts Saturday morning. High Wind Warnings and Wind Advisories
remain in effect for the areas noted above. Please see NPWMFR for
more details. Note: We currently have a wind advisory for only the
eastern half of Lake County. However, we are also expecting snow
at the same time that strong winds are occuring and the details on
the winds will be addressed in the winter weather products. Winds
along the coast, Shasta Valley and south end of the Rogue Valley
and Josephine/Douglas Counties will diminish late tonight into
Saturday morning. Winds will remain moderate to strong east of the
Cascades into Saturday morning, then they are expected to
gradually diminish Saturday afternoon from northeast to southeast.
Therefore places like Modoc County could experience moderate to
strong winds into Saturday afternoon. Winds should not longer be a
concern for all areas Saturday night as the upper trough moves
into the area.

SNOW- Snow will also be a concern, especially along the Cascades
into Siskiyou county and northwest Modoc County. These areas will
get moderate to heavy snow from this evening through at least
Saturday afternoon and there's a good chance for snow fall rates
to exceed an inch per hour at times. Note: The Mount Shasta area
(which includes I-5 south of Weed to Dunsmuir) and highway 89 are
at highest risk of experiencing heavy snow with snowfall rates
between 1-2 inches an hour tonight into Saturday morning. Highway
97 towards Weed is also at risk for moderate to heavy snow with
snowfall rates pushing to an inch per hour tonight into Saturday
morning. It's also worth noting visibilities in these areas could
also be reduced at times to a 1/2 mile or less. Moderate to heavy
snow is also likely along the Cascades and Siskiyous along with
strong winds, especially over the exposed areas, and it is not
out of the question snowfall rates could exceed an inch per hour
along the Mt. Ashland Ski road, highways 230 and 138 near Diamond
Lake and highway 62 towards Crater Lake. Highway 97 will also be
impacted by a combination of moderate to heavy snow and moderate
to strong winds. Storm total snow further east of the Cascades
(east of highway 97) will be less, but significant impacts are
still expected mainly due to visibilities being reduced to a 1/2
mile or less and could result in brief whiteout conditions tonight
into Saturday morning. Siskiyou Summit will also get significant
snow tonight into Saturday morning with up to a 12 inches possible
between this evening through Saturday afternoon. Because of the
above mentioned, this is likely to cause hazardous travel
conditions. Therefore it's highly recommended that folks stay home
and avoid traveling, especially from late this afternoon through
Saturday morning for the areas noted above. Winter storm Warning
and Winter Weather Advisories are in effect for the areas noted
above. Please see WSWMFR for more details.

RAIN- The heaviest precipitation is expected to arrive late this
afternoon along the coast and tonight inland. Because were expecting
gusty winds in the Rogue and Shasta Valleys Friday, these areas will
experience downsloping which could result in dry weather Friday
afternoon, with precipitation amounts limited Friday evening as the
front gets closer to these areas. It will be a different story for
the coast, coastal mountains, Cascades and Siskiyou County. 24 hour
storm total precipitation is expected to be between 4 and 5 inches
for the coastal mountains in southwest Oregon, and south coast, 1.5
to 2.0 inches for the north coast, 2 to 3 inches along the Cascades
and 3.50 to 4.50 inches from western through southern Siskiyou
County. Because of the expected high rainfall totals over the
coastal mountains and south coast, mud and rockslides could be a
concern, especially along highway 101.

In general, expect conditions to improve Saturday afternoon into
Saturday night, but light precipitation will continue through the
short-term forecast into the long term portion of the forecast.

.LONG TERM...Sunday 12/11 through Friday 12/16...The deep, high
amplitude trough axis will pass directly over the forecast area
Sunday morning, then dig farther to the southeast Sunday night into
Monday. This will keep showers in the area through the day Sunday,
and with the cooler airmass overhead, snow levels will hover between
2000 and 2500 feet. BY this time, the main moisture flow will be
clear of the region, so precipitation amounts, an therefore snow
amounts will be light, and for the most part, hit or miss. As the
trough work out of the area, showers will diminish from west to
east, with all activity expected to end by Monday morning. Generally
speaking, these events have a tendency to slow down a bit in time,
so there is a possibility that showers continue more into Monday
morning, but again, impacts should be minimal.

From this point onwards, there is a great deal of uncertainty in the
forecast. Models do show signs that a narrow, high amplitude ridge
will pass over the area Tuesday morning. Meanwhile, a trough within
the main belt of westerlies over the Gulf of Alaska is forecast to
split off from the flow, forming a cut-off low. By Wednesday, this
low takes up station somewhere off the Pacific coastline, and there
is a wide spread of location, and strength of the low, amongst the
ensemble suites. The pattern suggests that a blocking ridge then
forms somewhere in the northeastern Pacific, north of this low.
There are many possibilities from this point onwards, and our
forecast will depend greatly on where the low ends up, what type of
blocking ridge forms, and how strong the resulting pattern is.
Should the low shift to the east and reside over the forecast area,
we can expect cooler temperatures and widespread precipitation
chances by mid to late week, if the low stays offshore, however,
then we will remain under a weak ridge or deformation zone between
the cut-of low and the main trough over the central U.S., keeping us
dry with strong inversions and valley fog.

Amongst the ensemble solutions, there is no clear winner, with
solutions of both types, and everything in between, spread amongst
the runs. One thing we can say for sure is that we don not expect
any major storms, as the preferred storm track will remain well out
of our region. As a result, the long term forecast relied heavily on
a general model blend/NBM solution, with near normal temperatures
and little chance for precipitation. -BPN

&&

.AVIATION...09/18Z TAFs...Areas of MVFR cigs/vsbys with higher
terrain obscured and local areas of IFR cigs/vsbys in valley fog are
expected to clear by late morning. However, MVFR cigs/vsbys and
terrain obscurations will linger as a strong front brings another
round of rain/snow along with high winds to the area. Though strong
winds are expected at all terminals today, LLWS will remain a
concern at all local airports as winds aloft remain strong through
much of the TAF period. While MVFR/IFR conditions are expected in
areas of moderate to heavy rain, LIFR/IFR is expected in areas of
moderate to heavy snow this evening and tonight, such as in the
Mount Shasta City area.

The front is expected to pass through the area late in the TAF
period, with winds diminishing behind the front, but precipitation
lingering well into the morning, especially along northwestern and
western slopes. -BPN/BR-y

&&

.MARINE...Updated 200 PM PST Friday 9 December 2022...South winds
are ramping up over the marine waters early this afternoon as a very
strong Pacific cold front approaches the coast. Buoy observations
are already showing gale force winds and those will only increase
through this evening as the core of a coastal jet sets up within
about 30 NM of the coast. Storm force south winds of 40-50 kt are
expected with gusts of 60-65 kt, resulting in dangerous, very steep
and very high seas through tonight.

In these strong southerly wind events, there is potential for south-
facing beaches and ports to be impacted by the extreme wave action.
As such, we have a high surf warning in effect for areas south of
Cape Blanco, but particularly around Port Orford, where the
dock/jetty is prone to overwash from these waves.

The front will finally move inland Saturday morning. Winds will
diminish and become westerly, but very steep, short period seas will
continue. Then, a very high/steep northwest swell will build into
the waters Saturday afternoon and night. Seas gradually lower
Sunday into Monday morning but are expected to remain high and
steep. Seas then subside Monday afternoon into Tuesday with
relatively light winds. -Spilde

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...     Winter Weather Advisory until 4 PM PST Saturday for ORZ029-030.

     High Surf Warning until 4 AM PST Saturday for ORZ021-022.

     High Wind Warning until 4 AM PST Saturday for ORZ021-022.

     Wind Advisory until 4 AM PST Saturday above 1500 feet for
     ORZ023>025.

     Wind Advisory until 4 AM PST Saturday for ORZ026.

     Winter Storm Warning until 4 PM PST Saturday for ORZ027-028.

     Winter Storm Warning until 4 PM PST Saturday for ORZ029-030.

     Wind Advisory until 4 PM PST Saturday for ORZ031.

     Winter Weather Advisory until 4 PM PST Saturday for ORZ031.

CA...Winter Storm Warning until 4 PM PST Saturday above 3000 feet for
     CAZ080.

     High Wind Warning until 7 AM PST Saturday for CAZ081.

     Winter Storm Warning until 4 PM PST Saturday above 3000 feet for
     CAZ081.

     Winter Storm Warning until 10 PM PST Saturday for CAZ082-083.

     Winter Weather Advisory until 4 PM PST Saturday for CAZ084.

     Winter Storm Warning until 4 AM PST Sunday for CAZ085.

PACIFIC COASTAL WATERS...Storm Warning until 4 AM PST Saturday for
     PZZ350-356-370-376.

     Hazardous Seas Warning from 4 AM to 4 PM PST
     Saturday for PZZ350-356-370-376.

&&