High Surf in Oregon, January 9 to 10, 2024

Area Forecast Discussion
National Weather Service Medford OR
357 AM PST Tue Jan 9 2024

.SHORT TERM...Two strong frontal systems will impact the area
today through Wednesday. This will result in significant impacts
from heavy snow and gusty winds. The worst conditions will be felt
in the mountains, especially in the Cascades but significant
impacts are expected down lower passes and even some west side
valley floors. The worst and most widespread impacts are expected
with the second frontal system tonight into  Wednesday. Winter
storm warnings and winter weather advisories are in effect.
Please see the WSWMFR for details. Meanwhile, for areas along the
coast, moderate to heavy rain is expected along with gusty winds
today and Wednesday.

A cold front is moving inland across the area this morning and
will shift eastward later today. Snow levels will quickly lower
from 4000-5000 feet overnight/early this morning to around
2500-3500 feet during the morning then dropping to 2000-2500 feet
late this afternoon into this evening. Showers will continue this
afternoon into this evening behind this front as moist onshore
flow remains in place. With this frontal passage today, heavy snow
is expected, especially along and near the Cascades. At least
moderate snow amounts are expected east of the Cascades,
especially over the higher terrain and for the Highway 97 corridor
from Chiloquin north as well as over higher terrain in northern
California. As snow levels lower late today into this evening,
expect snow down to 2000 feet in showers.

Impacts from heavy snow and strong, gusty wind will increase
tonight into Wednesday as a stronger front arrives. Models
continue to show a compact low moving into northwest Oregon and
shifting southward tonight. This will bring a strong frontal
system across the area late this evening into Wednesday morning,
gradually shifting southward during the day on Wednesday. Snow
levels may vary considerably as this front moves into the area.
This evening, snow levels are forecast to be near 2000 feet or
slightly lower, but models are then showing snow levels briefly
rising some ahead of the front tonight (Tuesday night). We have
leaned towards the lower range for snow levels tonight (with
forecast snow levels 2000-3000 feet) given the models show a
potential for convective activity with weak instability in place
and strong jet aloft. With the frontal passage, high resolution
models also indicate a stronger band of precipitation moving
southward across the area late tonight into early Wednesday
morning. Snow levels are expected to fall as this frontal band
moves over the area, quickly lowering down to 1500 feet Wednesday
morning and locally down to 1000 feet. Heavy snow is expected for
elevations above 2000 feet with this frontal passage. Gusty winds
are also likely across much of the area with strong, gusty winds
over the mountains and into areas east of the Cascades. Wind
(gusting to around 40 to 60 mph over exposed higher mountains)
combined with heavy snow rates will result in periods of near
white out conditions at times, especially in the Cascades where
snowfall rates of 1 to 2 inches per hour are possible Tuesday
night and Wednesday morning. Snowfall amounts in the Cascades will
be measured in feet with this event. The National Blend of Models
is showing a high chance (80-100%) of at least 18 inches of snow
in the Southern Oregon Cascades from Lake of the Woods north and a
40-60% chance of more than 24 inches of snow. In the Siskiyous,
along the Highway 97 corridor north of Chiloquin and over the
mountains east of the Cascades and mountains across Siskiyou
County, there is a high chance (65-95%) for at least 8 inches of
snow Tuesday night through Wednesday and for the higher mountains
and Highway 97 corridor there is a 60-80% chance for 12 inches or
more of snow.

West of the Cascades, heavy snow impacts are expected for
elevations above 2000 feet with moderate snow impacts down to some
lower valley floors. Snow levels will vary though, making the
snow forecast tricky with this event. The highest potential for
accumulating snowfall will be late Tuesday night (beginning around
midnight) into Wednesday morning as the front moves from north to
south across the area with sharply lowering snow levels and
ongoing precipitation. Breezy to gusty winds are also expected,
ranging from gusts of around 15 to 25 mph in valleys to strong,
gusty winds (40-60 mph) over the higher mountains. Blowing snow
will result in very low visibilities at times, with the worst
conditions in the mountains.

Models show this front will shift south of the area by early
Wednesday afternoon with a cold, showery air mass in place late
Wednesday into Wednesday night. Impacts are expected to decrease
Wednesday evening through Thursday morning as showers lighten and
decrease in coverage. Cold late night/morning temperatures are
expected Wednesday night and Thursday morning across the area with
temperatures in the teens to single digits east of the Cascades
and into Northern California and in the mid 20s to lower 30s for
valleys west of the Cascades. Temperatures down to the mid 30s are
expected for coastal areas Wednesday night and Thursday morning.

&&

.AVIATION...09/06Z TAFs...Rainfall from an approaching cold front is
approaching southwest Oregon, with radar showing activity over North
Bend and approaching Roseburg. This first front will bring
widespread precipitation, with the highest amounts and most constant
activity over coastal ranges and the Cascades. Snow levels will
start at 5000 to 6000 feet ahead of the front, but will drop to 1500
to 2000 feet by the end of the TAF period. Rain and snow showers
through the day are expected to locally lower ceilings,
visibilities, and snow levels as well as obscure terrain. In
addition to rain and snow showers, widespread low level wind shear
is expected as guidance indicates winds 40 to 55 knots at 2000 feet.
Extra caution is encouraged.

Activity may calm slightly Tuesday evening, but another front
approach late Tuesday and into early Wednesday morning. Lower snow
levels and heavier precipitation are expected. -TAD

&&

.MARINE...Updated 215 AM Tuesday January 9, 2024...The first of two
fronts has passed through the region this morning, but gusty west
winds persist throughout the waters, with gale force winds north of
Cape Blanco. Meanwhile, large, long-period swell (16 to 23 ft @ 14
seconds) continues to build into the region. The combination of
these factors has resulted in very steep and hazardous seas through
the entire marine region.

Winds will subside slightly but remain gusty later this afternoon
and evening, but a second front tonight will bring more westerly
gales to the waters north of Cape Blanco. A band of strong winds
will move from north to south through the waters, though it is
expected that these will weaken below gale force by the time it
makes its way south of Cape Blanco. Due to the short period between
fronts, the Gale Warning has been extended to also encompass this
second strong front tonight.

Winds turn to the northwest and begin to ease Wednesday, though
they'll remain fairly gusty. The west swell will continue to create
very steep and hazardous seas through late Wednesday afternoon, with
seas gradually subsiding but likely remaining steep into the late
week. Another system is expected late in the weekend which will
bring another round of building seas and gusty winds. -CSP

&&

.BEACH HAZARDS...Updated 215 PM Monday January 8, 2024...Active
weather returns to the Oregon Coast this week with a heavy long
period swell arriving by early Tuesday morning. This will bring
dangerously large breaking waves of 23 to 29 ft to the coast and
shorelines of Curry, Coos, and Douglas Counties Tuesday into
Wednesday. All area beaches will be dangerous places to be during
this time as waves inundate beaches and surge into normally dry
areas. Additionally, infrastructure damage and significant beach
erosion can be expected. A High Surf Advisory is in effect from 4
am Tuesday through 10 pm PST Wednesday, and area beaches should be
avoided during this time.

&&

.PREV LONG TERM DISCUSSION... /Issued 305 PM PST Mon Jan 8 2024/

Long Term Overview:

Of note for the long term is the relatively light snowfall amounts
expected across mainly high elevation areas through the weekend, but
on Saturday higher amounts appear more likely and perhaps the most
impactful day in the long term.  Also of note is the potential for
breezy/gusty winds on the east side for both Thursday and Friday.

Further Details:

Starting Thursday, models are indicating a broad long wave trough
across the CONUS, with northwesterly flow over the PacNW. We stay
consistently in this pattern through Friday with good agreement
between the global models. This will bring weak embedded pieces of
energy over the area which will result in light snowfall amounts for
higher elevations. Starting Saturday, we are expecting a change with
the next upper low making its way towards the area. Each of the
deterministic models (GFS, European, and Canadian) have a slightly
different solution/track with the next closed H5 low. This
discrepancy between model solutions brings a lot uncertainty because
the track has significant impacts on where exactly we will see the
highest precipitation and strongest wind speeds. The Canadian is
faster and more progressive through the region; however, the GFS and
European are both slower and each with a slightly different track.
The GFS is farther north as it comes on shore versus the European
which is farther south. Those details will matter for the finer
details, but as of now it looks like either of these solutions will
bring precipitation to the region if they hold. Some of our higher
elevations like the Cascades will likely get snowfall. Depending on
which track wins will determine what kind of wind speeds we will
have to deal with. Additionally, the track will ultimately affect
the moisture fetch and therefore overall snowfall amounts. The
takeaway here is that hazardous travel conditions will be possible
for mainly areas above 5000 feet starting as early as Friday night
and going through Saturday evening.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning until 4 PM PST Wednesday for ORZ029>031.

     High Surf Warning until 10 PM PST Wednesday for ORZ021-022.

     Winter Storm Warning until 4 PM PST Wednesday above 2000 feet
     for ORZ023>026.

     Winter Weather Advisory from 10 PM this evening to 9 AM PST
     Wednesday for ORZ023-024-026.

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

CA...Winter Storm Warning until 4 PM PST Wednesday above 2000 feet
     for CAZ080>083.

     Winter Storm Warning until 4 PM PST Wednesday for CAZ084-085.

PACIFIC COASTAL WATERS...Hazardous Seas Warning until 4 PM PST
     Wednesday for PZZ356-376.

     Gale Warning until 1 AM PST Wednesday for PZZ350-370.

     Hazardous Seas Warning from 1 AM to 4 PM PST Wednesday for
     PZZ350-370.

&&

CC