High Surf in Oregon, October 24 to 25, 2021

Area Forecast Discussion
National Weather Service Medford OR
420 PM PDT Sun Oct 24 2021

.UPDATE...Updated the marine section.

&&

.AVIATION...24/18Z TAFs...A strong front will continue across the
area this afternoon through the early evening, bringing strong winds
and precipitation to the area with obscuration of higher terrain.
Low level wind shear will impact many areas, including KOTH, KRBG,
KMFR, and KLMT. The low level wind shear will abate after the front
passes through (about 21Z at KRBG and KMFR. Low level wind shear is
not expected on the east side as surface winds will be strong. Areas
of MVFR cigs and mountain obscuration may develop behind the front
late this afternoon into the early evening, mostly from the Cascades
west. The lower conditions will persist into Monday morning.
Freezing levels will be 9000-10000 feet ahead of the front, dropping
to 6000 feet behind the front this evening. Thunderstorms are also
possible this afternoon and overnight, mainly near shore, as an
unstable air mass moves overhead.

Gusty winds begin to diminish across most of the forecast area by
midnight tonight. The coast north of Cape Blanco will be the
exception where winds should continue to be gusty into Monday
morning. Behind the front, showers, mountain obscuration, and areas
of MVFR persist. The next weaker front will bring the next batch of
rain and broader coverage of MVFR to the coast Monday morning.

-Keene/DW

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.MARINE...Updated 200 PM PDT Sunday 24 October 2021...Exceptionally
deep low pressure well offshore of Washington will continue to track
towards Vancouver Island. Gales will continue north of Cape Blanco
through tonight while a historically large west swell builds to a
peak.  Along the shoreline, breaking wave heights around 35 to
40 feet are expected.

Conditions will be slow to improve with very high and very steep
seas continuing into Tuesday. Winds and seas will subside late
Tuesday. But, seas will likely remain steep at least through
Wednesday with active weather continuing through the week. -DW

&&

.BEACH HAZARDS...Updated 200 PM PDT Sunday 24 October 2021...Beaches
and coastlines will become hazardous due to very large and life-
threatening surf conditions as breaking waves build to 30 to 40 feet
from this evening to Tuesday morning. Historically large breaking
waves will create very hazardous conditions along beaches and area
shorelines. Waves will inundate beaches and surge into normally dry
areas. Stay off of beaches, rocks, jetties, and piers.
Infrastructure damage and significant beach erosion can be expected.

&&

.PREV DISCUSSION... /Issued 256 PM PDT Sun Oct 24 2021/

SHORT TERM...A very deep low continues to slowly work its way
towards Vancouver island, and is expected to arrive Monday
afternoon. However, before that happens, a combination of factors
will continue to bring an active pattern through the next several
days. The strong south to north gradient that brought strong
winds to the coast and the Shasta Valley into the Rogue Valley in
Jackson county has loosened as the front moved across the west
side into eastern Oregon and northern California. With strong 700
MB winds the strong winds east of the Cascades will continue into
the wee hours of Monday morning. A very well defines line of
precipitation moved through the waters with numerous lightning,
but no increased winds were observed, but heavy rain accompanied
them and no further lightning was observed after it moved inland.
Broad upper level divergence in the 140 KT jet continues into
overnight before the less favorable left entrance region of the
jet moves in Monday morning, shifting the bulk of the
precipitation east by late afternoon. A very cold air mass moves
inland later this afternoon, and isolated thunderstorms are
possible over the coastal waters and inland a bit before the
surface support fades with cooling surface temperatures decreasing
as we head towards sunset.

The next system in line come in on a northwesterly aligned front,
with snow levels dropping down to the Cascade passes during the
day Tuesday. Snow amounts got close to advisory levels in the
Crater Lake area, but road and surface temperatures are still warm
and web cams in this are are showing snow melting almost
immediately and will not issue an advisory at this time in spite
of the early season nature of this event, and will evaluate again
later. The warm front precipitation spills over to the east side
Tuesday, with the flow behind in strong due westerly winds
keeping the bulk of the precipitation from the Cascades westward.
-Sven

LONG TERM...Wednesday through Sunday...Residual showers will
dissipate through the course of the day Wednesday as a ridge of high
pressure tries to nudge northward from the south. This ridge will
also be competing with the next system to bring precipitation to the
Pacific Northwest. The main questions with this pattern will be how
far north the ridge builds, and thus where the bulk of the
precipitation will land. For now, ensembles and their operational
deterministic counterparts show that the bulk of the precipitation
associated with this atmospheric river will move into Washington
State on Wednesday night, leaving us on the southern periphery with
a warm front. We will hold onto the some light precipitation
chances, largely across the coast and in the Umpqua basin, and
possibly for the Cascades as well. That being said, impacts are
generally not expected in the midweek timeframe.

This system will push the ridge eastward away from our area as the
front sinks southward over the next couple of days (through Friday).
This could bring us some additional precipitation, even to areas
east of the Cascades. However, the front will lose some energy
pushing the ridge eastward, so expect precipitation to be relatively
light. Meanwhile, at the southern edge of the front, an area of low
pressure will cut off and develop. This low will push inland,
bringing additional precipitation chances near the area where it
makes "landfall", but ensembles are relatively split as to the
location of this low with ECMWF ensembles keeping a more northerly
track giving us more needed precipitation and the GEFS brings a more
southerly track giving the needed precipitation to central and
northern California. Models will undoubtedly show significant
changes between now and its landfall which is forecast for Saturday
night into Sunday. So this will need to be tracked. Have gone with
the National Blend of Models for the extended forecast as it seems
to have a decent balance.

Overall, the forecast while remaining relatively active will be
light on impacts due to the light nature of precipitation and
relatively high snow levels. -Schaaf

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning until 2 AM PDT Monday for ORZ030-031.
     Wind Advisory until 2 AM PDT Monday for ORZ029>031.
     Coastal Flood Warning until 7 AM PDT Monday for ORZ021-022.
     High Surf Warning until 5 AM PDT Tuesday for ORZ021-022.

CA...High Wind Warning until 2 AM PDT Monday for CAZ085.
     Wind Advisory until 2 AM PDT Monday for CAZ085.
     Flood Watch until 5 PM PDT this afternoon for CAZ080-082.
     Flash Flood Watch until 5 PM PDT this afternoon for CAZ080-083.

Pacific Coastal Waters...
     Gale Warning until 8 AM PDT Monday for PZZ350-370.
     Hazardous Seas Warning from 8 AM Monday to 5 AM PDT Tuesday for
     PZZ350-370.
     Hazardous Seas Warning until 5 AM PDT Tuesday for PZZ356-376.