High Wind in Oregon, October 24, 2021

Area Forecast Discussion
National Weather Service Medford OR
333 AM PDT Sun Oct 24 2021

.DISCUSSION...The latest Satellite image clearly shows the surface
low rapidly deepening near 134W and 45N. The closest buoy
observation (east of the surface low) is reporting a pressure of
964.1 mb. There's good agreement the low will bottom out close to
943 mb this morning, before gradually increasing this afternoon as
it begins to fill and curves northeast towards Vancouver Island. To
put this in some context, hurricanes that are classified category 3
or 4 can have surface low pressure close to this value. Also one
more thing to note is an offshore buoy (buoy 46006) that is
currently south to southwest of the surface low had reported total
combined seas at 40 feet with wind waves at 39 feet! Pretty
impressive stuff. Meanwhile, gusty winds are occurring in areas
where we expected them to be a concern. At 12:45 am pdt, Onion
Mountain reported a wind gust of 69 mph, but has since dropped off
some in the last couple of hours.

Strong winds are likely at the south coast, headlands, Shasta Valley
and east of the Cascades. 700 mb flow of 60-75 kt is a given for
northern California and southern Oregon ahead of the front, and with
strong surface gradients, strong winds are likely for our typical
wind-prone areas. The Rogue Valley will also be under the threat for
moderate to strong winds as well. Various high wind warnings and
advisories remain in effect for the areas noted above. One thing to
note: With leaves still on trees and wet soils, there is an
increased concern for falling or damaged trees. Details on all the
wind headlines can be found at NPWMFR.

Moderate to heavy precipitation is likely is likely for Northern
California which is pretty good agreement with the IVT (Integrated
Water Vapor Transport) which puts the bulls eye in northern
California.  That's not to downplay the amount of rain southwest
Oregon, specifically the coast and coastal mountains, but the
duration won't be as long. The focus of concern for heavy
precipitation will be in northern California and mainly during the
morning hours. The core of heavy precipitation will then shift south
of our area early this afternoon with precipitation rates
diminishing. Drought conditions have left rivers and reservoirs low
and with plenty of capacity, so main stem flooding is not likely,
but small streams and and location with blocked drainages could see
ponding or overflows. However, given were expecting moderate to
heavy rain through the morning hours, flooding is also possible in
portions of western Siskiyou county and around the Mount Shasta
area. Flash Flood Watches remain in effect for burn scars in
Siskiyou County, and highway 97 near Whitney Creek. Details can be
found at PDXFFAMFR. Also an areal flood watch remains in effect,
please see PDXFAAMFR for more details on the Flood Watch.

The front will sag south into northern Cal this afternoon with
precipitation rates diminishing. Meanwhile the surface low will move
inside of 130W this evening as it moves northeast towards Vancouver
Island. At the same time an upper low will send multiple impulses
through our area resulting in a continuation of showers Sunday night
through Monday. Snow levels will come down tonight between 4500 and
5000 feet by Monday morning. It's a pretty good bet roads leading up
to Crater Lake and Diamond Lake will have road snow by Monday
morning, but the subsurface road temperatures are still likely
holding heat that will put a cap on the amount of road snow in these
areas. Lake of the Woods will be a close call, but could not rule
out some roadside slush by Monday morning.

The upper trough will move east with a relative break in the action
Monday evening, but once again, this will not last long with a warm
front approaching later Monday night into Tuesday. This warm front
is not expected to be a big precip producer and snow levels will be
rising late Monday through Tuesday, therefore snow and flooding
concerns are expected to be low.

The warm front is expected to fizzle out Tuesday night as 500 mb
heights rise as a broad upper ridge builds into the area and it's
possible we could catch a break in the weather with an increasing
chance for dry weather Wednesday-Friday. Of note: the operational
GFS and ECMWF show another warm front moving through the area
Wednesday night into Thursday morning, however the GFS typically
overdoes warm frontal precipitation and given the fact 500mb heights
actually increase some during this time, the amount and coverage
area of precipitation suggested by the GFS is suspicious. Digging
deeper into the ECMWF ensembles members shows the majority of the
members show no precipitation during this time period. Given the
above mentioned reasoning, have kept in a slight chance mainly west
of the Cascades and in the northwest part of our forecast area.
-Petrucelli

&&

.AVIATION...24/06Z TAFs...A strong front will move onshore Sunday,
bringing strong winds and precipitation to the area. Initially
conditions will be mostly VFR with obscuration of higher terrain.
Low level wind shear will develop later tonight, including KOTH,
KRBG, KMFR, and KLMT. The low level wind shear will abate after the
front passes through (about 18Z at KOTH, 21Z at KRBG and KMFR),
except at KLMT where surface winds will become quite strong ahead of
the front.  Areas of MVFR cigs will develop behind the front late
Sunday afternoon into Sunday evening, mostly from the Cascades west.
The lower conditions will persist into Monday morning. Freezing
levels will be 9000-10000 feet Sunday morning, dropping to 6000 feet
behind the front Sunday evening.

&&

.MARINE...Updated 2 AM PDT Sunday 24 October 2021...Very deep low
pressure well offshore will send a strong front onshore this
morning. Dangerous marine conditions are expected through at least
Monday. Storm force southerly winds are expected from Cape Blanco
northward with gales south of Cape Blanco this morning. Gale force
winds will occur north of Cape Blanco this afternoon through
tonight. Historically large west swell will follow the front late
this afternoon and very high and very steep seas will continue into
Tuesday. Along the shoreline, breaking wave heights around 35 feet
are possible.

Very high and very steep seas will persist into Tuesday. Winds will
subside Tuesday, but seas will remain steep through Wednesday.
Keene

&&

.BEACH HAZARDS...Updated 2 AM 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 28 to 37 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.

&&

.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.
     High Wind Warning until 11 AM PDT this morning for ORZ021-022.
     Coastal Flood Warning from 5 PM this afternoon to 7 AM PDT
     Monday for ORZ021-022.
     High Surf Warning from 5 PM this afternoon to 5 AM PDT Tuesday
     for ORZ021-022.
     Wind Advisory until 11 AM PDT this morning for ORZ026.

CA...High Wind Warning until 2 AM PDT Monday for CAZ085.
     Wind Advisory until 2 AM PDT Monday for CAZ085.
     Flood Watch through this afternoon for CAZ080-082.
     Flash Flood Watch through this afternoon for CAZ080-083.
     High Wind Warning until 2 PM PDT this afternoon for CAZ081.

Pacific Coastal Waters...
     Gale Warning until 11 AM PDT this morning for PZZ356-376.
     Hazardous Seas Warning from 11 AM this morning to 5 AM PDT
     Tuesday for PZZ356-376.
     Storm Warning until 11 AM PDT this morning for PZZ350-370.
     Gale Warning from 11 AM this morning to 8 AM PDT Monday for
     PZZ350-370.
     Hazardous Seas Warning from 8 AM Monday to 5 AM PDT Tuesday for
     PZZ350-370.