Sneakerwave in Oregon, November 24 to 26, 2023

Area Forecast Discussion
National Weather Service Medford OR
530 PM PST Fri Nov 24 2023

Updated AVIATION Section

.DISCUSSION...A trough of low pressure sits over the dessert
southwest and will progress to the east, while a dome of high
pressure begins to build overhead. This will form an omega block
over the region and result in an influx of cold air and a strong
subsidence inversion settling over the region. Fortunately, the
omega block is expected to be broken up in the extended portion of
the forecast period.

For the cold temperatures, a freeze warning and frost advisory both
exist for portions of the Oregon coast. Freezing conditions are
expected through much of inland Coos County including Myrtle Point,
Coos Bay, Coquille, and Powers on Saturday. It's worth noting that
beginning on the first of December, we will begin to only issue
freeze warnings for the immediate coast. These will likely be the
final cold related headlines until the end of February and we start
to consider them again.

The omega block is inducing east winds along the higher terrain and
a strong subsidence inversion. This is resulting in gusty winds
persisting overnight along ridges and will begin eroding the
moisture that has been producing fog and stratus at night. While
tonight fog is still expected to form in westside valleys with some
areas receiving a loftier stratus layer, the extent of coverage is
expected to reduce each night.

The subsidence inversion will also increase the amount of stagnating
air for the entire region of SW Oregon and NorCal. For air
stagnation we look for mixing heights near or below 1000 feet,
mixing winds in that layer less than 5 kt, and lasting for no less
than 48 hours. Given the current data, we don't formally meet
that criteria because of mixing heights over the next few days
vary between 1000 and 2000 feet. These conditions will still
result in poor outdoor burning conditions and, meteorologically
speaking, could reduce air quality. We will be evaluating over the
next few model runs if an air stagnation advisory is needed;
which would be most likely for Sunday and Monday, November 26 &
27.

This pattern will stick around through the middle of next week until
a cut-off low moves down the Pacific coast. This will introduce
some low chances for rain starting as early as Tuesday night. The
better chance for rain resulting directly from this low is on
Wednesday with chances peaking around 30% with less than 0.1" of
rain forecast. The cut-off low will result in the large scale flow
coming out of the northwest, leading to a showery pattern with
lower snow levels. The chance for precipitation increases to
30-50% (for now...it is expected to increase further), with snow
levels settling somewhere between 3000 and 5000 feet.
-Miles

&&

.AVIATION...25/00Z TAFs...High pressure building in east of the
Cascades will lead to dry offshore flow (ENE winds) with VFR
prevailing overnight through Saturday. The low dewpoint this
afternoon at Medford (24F)@01Z is a good indicator of the drier
air mass and fog formation at the airport is unlikely. However,
just enough low-level moisture could lead to IFR freezing fog in
some of the west side valleys very late tonight or toward daybreak
Saturday. This is most likely in the Umpqua Basin at Roseburg,
portions of the Rogue Valley nearest the Rogue River (Grants Pass)
and also the Illinois Valley. -Spilde

&&

MARINE...Updated 200 PM Friday November 24, 2023...Strong northerly
winds over the water continue, with the strongest winds (25-30 kts)
south of Cape Blanco and beyond 10nm from shore and 15-25 kt winds
over all other waters. These winds will continue to combine with
northwest swell to sustain very steep seas in waters 10 nm and
beyond from the shore and steep seas for waters closer to shore. A
Hazardous Seas Warning continues for outer waters through Saturday
at 5 AM and a Small Craft Advisory is in place for inner waters.
After Saturday 5 AM, northerly winds will calm but the northwest
swell will remain and maintain steep seas through all waters. The
Small Craft Advisory will cover all waters from 5 AM Saturday to 5
AM Sunday.

From Sunday morning and through the week, light northwest swell
continues. Winds will be light through Wednesday with the direction
generally east to southeasterly. Wind direction will shift to
northerly after Wednesday and increase somewhat but still remain
below advisory criteria.  Seas also look to remain below advisory
levels through most of next week.
-TAD/Miles/Sargeant

&&

.BEACH HAZARDS...Updated 200 PM Friday November 24, 2023...A
moderate risk for sneaker waves is expected from the evening of
Friday, November 24 through at least the evening of Saturday,
November 25. A beach hazards statement has been issued. As this
sneaker wave event is expected during a King Tide event, more areas
of beach and coastline could be exposed to the sneaker wave threat
than normal. Even outside of a King Tide, waves can run up
significantly farther on a beach than normal, including over rocks
and jetties. These sneaker waves can suddenly knock people off of
their feet and quickly pull them into the cold ocean waters,
resulting in serious injury or death. Waves may also lift driftwood
logs, trapping anyone caught underneath.
-Spilde/Miles

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Beach Hazards Statement from 7 PM PST this evening through
     Saturday evening for ORZ021-022.

     Frost Advisory from 2 AM to 9 AM PST Saturday for ORZ021.

     Frost Advisory from 4 AM to 10 AM PST Sunday for ORZ021.

     Freeze Warning from 2 AM to 9 AM PST Saturday for ORZ021.

CA...None.

PACIFIC COASTAL WATERS...Beach Hazards Statement from 7 PM PST this
     evening through Saturday evening for PZZ350-356.

     Frost Advisory from 2 AM to 9 AM PST Saturday for PZZ350.

     Small Craft Advisory until 4 AM PST Sunday for PZZ350-356-370.

     Hazardous Seas Warning until 4 AM PST Saturday for PZZ356-370-
     376.

     Small Craft Advisory from 4 AM Saturday to 4 AM PST Sunday for
     PZZ376.

&&