High Wind in Oregon, December 1, 2023

Area Forecast Discussion
National Weather Service Medford OR
901 AM PST Fri Dec 1 2023

.DISCUSSION...Snow covered roads are the norm looking at cameras along
the Cascades this morning. The heaviest snow of the day will be
falling along the Cascades through 10 this morning with an 80-100%
probability of seeing 1" per hour snowfall rates. The current
Advisory and Warnings are on track through this weekend, with the
latest one lasting through Saturday evening for the Southern
Oregon Cascades and Siskiyou mountains. Later this afternoon and
into the evenings more spots will have a pause in the
precipitation before another swath off the coast moves eastward
through the morning.

Rainfall amounts have reached 0.50"-0.75" for the coast including
at North Bend and Agness. Summer Lake had a peak gust this
morning at 50 mph, and the Wind Advisory will be in effect until
Sunday morning. Today will focus on fine-tuning forecast details
for this system and looking at the continuing active pattern next
week. -Hermansen

&&

.AVIATION...01/18Z TAFs...A complicated set of TAFs are expected
over the next 24 hours with a wide range of ceilings, visibilities,
and precipitation in the forecast. Generally expecting a range of
MVFR to IFR conditions, but expecting more of the MVFR conditions.
Terrain obscuration is expected in periods of moderate rain and
snow. Snow levels will hover around 4000 to  4500 feet, so rain
looks to be the primary precipitation type for most terminals, but
Klamath Falls (KLMT) will have snow in the forecast. The TAFs will
continue to be busy through this cycle with brief breaks in
precipitation expected. Also of note is the breezy to gusty wind
speeds expected for KLMT this afternoon. -Schaaf/Guerrero

&&

.MARINE...Updated 830 AM Friday December 1, 2023...Active
weather will persist well into next week with multiple fronts
expected to pass through the region. A Hazardous Seas Warning is in
place for the northern waters through 5 PM and a Small Craft
Advisory will continue for southern waters. Northern waters will
calm slightly this evening. A Small Craft Advisory will cover all
waters through Saturday at 5 PM.

A particularly strong system is expected to arrive Sunday morning,
bringing strong southwesterly winds. With westerly swell continuing
to move into the waters, steep or very steep and hazardous seas are
possible Sunday and could continue into the week. Additional
guidance and observations will help to determine the exact timing
and coverage of expected hazards.

-Guerrero

&&

.PREV DISCUSSION... /Issued 418 AM PST Fri Dec 1 2023/

DISCUSSION...Active weather will continue this weekend into next
week as several systems impact the region, bringing widespread
rain and snow to elevations above 4000 feet. Currently, we're
sandwiched between systems, with a cold front moving through the
Intermountain West to our east, and another frontal system
approaching the coast. A intensifying jet aloft will help support
the incoming system, increasing lift and strengthening the lower
level winds. Near due west winds aloft at 700 mb will increase to
45-55 kt this morning. This is an ideal direction for orographic
enhancement over the coastal mountains and Cascade Range, and the
increasing low-level jet will also exacerbate precipitation over
the mountains.

This is all to say that precipitation will become heavy
over the mountains this morning, especially in the Cascades with
snow levels hovering around 4,000 feet today. High-resolution
models (the HREF) are indicating 90%+ chances for 1" an hour
snowfall rates in parts of the Cascades after 7 AM today, and
30-50% chances for 2" an hour in the same areas. This in addition
to gusty winds and blowing snow will make for hairy conditions
over the Cascades, making travel over Cascade passes difficult to
impossible. The Winter Weather Advisory transitions to a Winter
Storm Warning above 4000-4500 feet this morning to cover this
threat. Accompanying the snow, we're expecting advisory-level
gusty winds

Precipitation will turn showery/periodic this evening, but the
break in precipitation will be brief as another system moves in
early Saturday. Warm southwesterly flow will bring snow levels
from 4000-4500 feet to 5500-6000 through the day Saturday. Aloft,
fairly strong westerly winds will continue to enhance orographic
precipitation over the coastal mountains and the Cascades, though
the higher snow levels will restrict snowfall to only the higher
peaks by late Saturday. The Winter Storm Warning will continue
through this period due to continued heavy snow and gusty winds
in the Cascades. Today through late Saturday, the Cascades will
see 10-35" of snow, with higher amounts possible locally over the
highest peaks. Other regions will see far less snow due to
raising snow levels, with generally less than 2" expected for most
areas east of the Cascades, except for 5-10" over the Modoc/south
Lake County Warner Mountains and along Winter Rim/Ridge. Snow
levels will then continue to rise over the weekend to 7,000+ feet
with continued warm air advection.

-CSP

LONG TERM...Sunday (12/3) through Thursday (12/7)...The active
pattern will continue into the extended period. There is some wide
variation across the model suites regarding the timing and nature
of the individual systems. There has been a trend towards a
somewhat drier forecast for portions of the extended term within
the deterministic GFS/EC and many of the member runs. As typical,
it appears the NBM is lagging behind in this trend, so it still
maintains a hefty chance of rain throughout the extended. It is
difficult to illustrate this given the current state of the
forecast process, and therefore the forecast products still
suggest that there is a constant threat of precipitation. However,
we are fairly confident that there will be a roughly 24 hour
break in the action Monday. Hopefully the timing details will
become clearer over the next several forecast cycles.

The most likely scenario will be for us to see a brief lull early
Sunday morning as the Saturday system exits and the next system
approaches from offshore. We will still see a general westerly flow
aloft, and this typically gives us good upslope precipitation
production, especially along the coast and the western slopes of
the Cascades. This next system then moves onshore during the day
Sunday, but the model solutions are trending the bulk of the
system farther north, mainly due to the difficulty of the upper
level trough to dig into the larger ridge lying over and just
offshore of California. The trailing edge of the surface front
should still bring us a precipitation and winds, but the bulk of
the moisture transport and dynamics will keep to the north, more
towards Portland and Washington.

The trough exits and the ridge attempts to build back over southern
Oregon Sunday night into Monday. This is where things should trend
drier than previously thought, though the chance for showers does
not completely end (due to some overrunning along a warm front)
before the next system arrives Tuesday into Wednesday, with more
rain and wind.

Fortunately for travel concerns, snow levels are expected to remain
well above 5000 feet for the vast majority of the extended period,
so winter impacts will be minimal. We will have to keep an eye on
hydrological concerns, however, as despite the lack of any one
period of heavy rain, the quick successive storms could add up,
leading to rises on area rivers and streams.

-BPN

BEACH HAZARDS...Active weather continues well into next week. A
series of fronts will move through the region during this time along
with multiple moderate swell trains. An extended period of sustained
wave action is expected. Breaking waves of 15 to 20 ft will coincide
with higher than normal ocean levels, leading to an increased risk
of beach erosion. Additionally, there is a minor risk of sneaker
waves as these swell trains build into the waters. Confidence is
low, however, considering wind wave interference is likely to limit,
but not completely negate the sneaker threat. If venturing to area
beaches during this time, use caution when visiting and remember to
never turn your back on the ocean! /BR-y/Hermansen

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Beach Hazards Statement from late tonight through late Monday
     night for ORZ021-022.

     Winter Storm Warning until 4 AM PST Saturday above 4000 feet for
     ORZ025.

     Winter Storm Warning until 10 PM PST Saturday above 5500 feet
     for ORZ027-028.

     Winter Weather Advisory until 10 AM PST Saturday above 4000 feet
     for ORZ029.

     Winter Storm Warning until 10 AM PST Saturday above 4500 feet
     for ORZ030.

     Wind Advisory until 4 AM PST Sunday for ORZ031.

CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory until 4 PM PST Saturday
     for PZZ356-376.

     Hazardous Seas Warning until 4 PM PST this afternoon for PZZ350-
     370-376.

     Small Craft Advisory from 4 PM this afternoon to 4 PM PST
     Saturday for PZZ350-370.

&&