High Wind in Oregon, November 19 to 20, 2024

Area Forecast Discussion
National Weather Service Medford OR
1000 AM PST Tue Nov 19 2024

.UPDATE...Aviation Discussion updated (see below). Additionally,
based on analysis of IVT values from the ECMWF, it would support a
strong Atmospheric River system moving into the coast of southwest
Oregon and Northern California. We will continue to monitor the rain
and snow forecasts and expected river conditions.

&&

.AVIATION...19/18Z TAFS...Light precipitation is starting to spread
inland this morning, mainly affecting the coast, Siskiyou county and
into the Cascades. This is bringing higher mountain obscurations and
areas of MVFR conditions. Winds are also beginning to increase this
morning at the coast and over higher terrain.

A very strong front will affect the region this afternoon and
through the remainder of the TAF period. The main impact to aviation
with this front will be very strong winds area wide. While the
strongest winds are expected along the coast, in the Shasta Valley,
across the high terrain and east of the Cascades, even the typically
sheltered valleys will experience strong winds today and tonight.
Even with strong surface winds, low level wind shear (LLWS) will
affect all areas today and tonight with wind shear values of 45 to
60 kts for inland areas and 60 to 80 kts along the coast and over
the marine waters. Expect LLWS to develop around 18z at the coast,
then spreading inland between 20z-00z. Wind impacts will continue
into Wednesday morning, mainly east of the Cascades and into the
Shasta Valley.

Overall, a mix of MVFR/low end VFR conditions will prevail this
afternoon with lowering conditions expected along the coast and in
the Mt Shasta region as heavy precipitation moves into the region
between 21-00z. MVFR and IFR is likely to increase over southwest
Oregon and northern California tonight and Wednesday morning. -CC

&&&

.SHORT TERM...Models continue to track a deepening low pressure
towards the region later today. This low is currently
located well offshore of the Northern Oregon coast near 44.7N
132.85W with an estimated central pressure of 976 mb. Models
continue to show this low rapidly deepening to around 945 mb or
lower as it shifts north-northeastward. A very strong front is
associated with this deepening low, which will near the southern
Oregon coast this afternoon and move onshore this evening, then
gradually pushing inland tonight into Wednesday. This is an
unusually strong storm with high impacts expected from high winds
(up to hurricane force gusts, especially along the coast and
coastal waters), heavy rain and heavy snow for portions of the
area.

Extremely strong winds are expected as this front moves onshore.
Models continue to show a 90-100 kt low level jet moving onshore
as the front nears. Hurricane force wind gusts are expected to
occur over the coastal waters and for capes and headlands along
the coast with very strong, damaging winds (nearing hurricane
force gusts) along other coastal areas. Inland, moderate to strong
winds are likely for most all areas of the CWA as this front
moves into the area late today into Wednesday.

Additionally, rain and snow will bring impacts to the area.
Satellite imagery, shows strong moisture plume with this front,
creating an atmospheric river system aimed at the coast of
southern Oregon and northern California. Integrated moisture
transport values exceed 800 kg/ms as this moisture moves into the
northern California and far southern Oregon coast. This represents
a moderate to strong atmospheric river event, with heavy rain
likely along the coast and coastal mountains and heavy
precipitation inland. Heavy rain along the coast and inland into
portions of the area west of the Cascades will allow significant
rises on mainstem rivers and we are monitoring the potential for
river and stream flooding, particularly for the Coquille River
and small streams west of the Cascades.

Snow levels will be relatively high along the coast (5000 to 6000
feet) but inland will be closer to 3000 to 4000 feet (and locally
down to 2000 feet in the Mount Shasta City area). With moderate
to heavy precipitation expected to move inland, late today into
Wednesday, this will bring heavy snow impacts to the mountains,
Mount Shasta City area and some areas east of the Cascades. Heavy
snow combined with strong, gusty winds is expected to create
extremely dangerous travel conditions. Additionally, the
potential of heavy wet snow down to lower valley floors in the
Mount Shasta area, may result in power outages and a potential for
roads to become impassible. Heaviest snowfall is forecast this
evening through Wednesday morning. The SREF supports a chance
(30-50%) for snowfall rates to exceed 2 inches/hr at times in and
near the Mount Shasta area.

Residents and travelers should monitor forecasts for expected
conditions as this storm brings high winds along with areas of
heavy rain and heavy snow and avoid travel in the worst hit areas.

&&

.MARINE...Updated 200 AM PST Tuesday, November 19, 2024...Steep seas
and gusty southwest winds will persist through early this morning
with conditions remaining hazardous to small craft. Conditions
rapidly deteriorate later this morning due to a surface low pressure
in the NE Pacific rapidly deepening as it heads NE just outside
130W. This system will "bomb out" (a pressure drop of 24 mb or more
in 24 hours) as it reaches 46N and 132W by this evening, and this is
a classic pattern for bringing very strong winds over the marine
waters. A very strong cold front and associated atmospheric river
will move toward the coast, impacting the marine waters this
afternoon into Wednesday morning. There is high confidence in very
strong sustained storm force winds (45-60 kt with hurricane force
gusts of 65 to 70 kt) and very dangerous mountainous seas of 30 to
35 feet. This strong of a storm occurs, on average, about once every
ten years. Mariners should expect these dangerous wind and sea
conditions to persist through Wednesday morning, with additional
hazardous conditions likely through Friday.

Winds will gradually ease Wednesday morning into the afternoon and
remain at or just below advisory criteria into Thursday morning.
Seas, however, will remain very high and very steep with warning
level seas likely to continue during this time frame. Southerly
winds begin increasing again on Thursday as another low pressure
deepens inside of 130 W late Thursday into Friday. Though there are
varying solutions on how strong/deep this next low pressure system
becomes, it does look weaker compared to what is expected later
today. That said, a deepening surface low inside of 130 W does tend
to result in strong winds and there is the potential for a round of
southerly gales Thursday afternoon into Friday. Once we're a little
farther into the big event later today, additional headlines will
likely be issued for the next system.

The overall sea state does look to improve for the weekend as the
upper level pattern weakens, but expect unsettled weather to
continue. /BR-y

&&

.BEACH HAZARDS...Updated 200 AM PST Tuesday, November 19, 2024...A
strong frontal system will move through the region this afternoon
into Wednesday, producing very strong and damaging south winds with
mountainous seas. These seas will result in dangerously large
breaking waves of 25 to 30 ft and very dangerous surf conditions
through Wednesday afternoon. The largest breaking waves are expected
along the south facing shorelines, such as the beaches near
Brookings, Port Orford, and Cape Blanco. Waves will inundate
beaches, push large logs up the beach, and surge into normally dry
areas. Infrastructure damage and significant beach erosion can be
expected. Beaches should be avoided during this time due to these
dangerous conditions and please exercise extreme caution if you risk
going to area beaches during this storm. /BR-y

&&

.PREV DISCUSSION... /Issued 411 AM PST Tue Nov 19 2024/

DISCUSSION...Satellite image is showing the beginning stages of a
significant storm taking shape over the eastern Pacific that has been
messaged in our forecast discussion, and various other products for
the past several days. This storm is one of the stronger storms we
have seen in at least a few years in terms of wind, heavy
precipitation and heavy snow for the Cascades and Mount Shasta area.

Three major impacts of this storm will be strong winds, moderate to
heavy precipitation and moderate to heavy snow. Details on each
follow below.

* WINDS through Wednesday...We will see some of the strongest
  winds we have seen in several years as this storm system passes
  through the area later this morning into Wednesday. The system
  itself is an almost perfect classic scenario for strong winds
  here in our forecast area: a rapidly deepening surface low
  approaching or crossing 130 degrees W, concurrent with the cold
  front passing onshore. There's good agreement mean sea level
  pressure gradients reaching -11 mb between North Bend and Arcata
  and also between Medford and Redding. Typically, coastal and
  inland high wind warnings (and marine storm force wind warnings)
  only need to reach -8, so we are well past this threshold. In
  addition, some of the high res model winds at 850mb (a good way
  to gauge the maximum possible marine and coastal surface wind
  gust speeds) are approaching 95 kt late this afternoon into
  early this evening, which are some of the highest speeds seen at
  that level in quite some time. Meanwhile at 700 mb (a good
  measure of maximum gusts over and east of the Cascades), speeds
  are approaching 75 to 80 kt. In basically every measure we look
  at when analyzing and forecasting high winds, this storm looks
  to surpass almost all thresholds, with a few exceptions.

* Winds will begin increasing at the coast towards midday, and will
  then peak in the evening before gradually diminishing through
  Wednesday morning. Areas west of the Cascades, including in the
  Shasta Valley, will follow the same timeline but about 3-6 hours
  later (peaking in the late evening and overnight), and east of the
  Cascades about 6 to 9 hours later (generally late Tuesday night
  but before sunrise Wednesday).

* The following wind headlines remain in effect: High Wind Warning
  at the coast, in the Shasta Valley, and across the East Side, and
  Wind Advisories for almost all of the the inland areas west of the
  Cascades. It should be noted that for the inland areas west of the
  Cascades, areas of higher terrain or in the southern Rogue
  River/Bear Creek valley near Ashland may briefly reach High Wind
  criteria right when the front passes. Some of the high res models
  are hinting at a more southerly or even a slight southeasterly
  component which result in higher wind speeds later this afternoon
  and evening.

* Areas along and east of the Cascades, and in the far southern
  Shasta Valley, will see these winds combining with snow, and this
  could result in near-whiteout conditions at times due to blowing
  and drifting snow. For almost all areas, road travel could be
  difficult due to strong winds, especially if it is a crosswind
  over roadway and/or if you are in a high profile vehicle. If you
  intent to travel anywhere in the area during the time of the
  storm, it is advised to make alternate plans and travel at another
  time.

* RAINFALL: Heavy precipitation is likely west of the Cascades, with
  2 to 5 inches of rainfall along the coast and into the  coastal
  mountains and across southwest Josephine and western Siskiyou
  county. 0.75 to 2 inches is likely for valleys in  Douglas,
  northern Josephine, Jackson and central Siskiyou  County. Some of
  this will fall as snow, over the  mountains/higher terrain and Mt
  shasta area. With the heavy  precipitation, rapid rises in rivers
  and small streams are expected. Current guidance suggest it will
  be a close call for minor flooding along the Coquille River and
  flooding for small streams, especially along the coast and into
  the Umpqua Basin. Please see the ESFMFR for details. One other
  thing to note, because of the downsloping winds in the Rogue
  Valley (strong south to southeast flow) this will look to limit or
  keep precipitation at bay until early this evening and it could
  end up dry for most, if not all the daylight hours today.

* SNOWFALL: Heavy snow is expected to impact the mountains
  (Cascades, Siskiyous and mountains in Western Siskiyou Co.) and
  the Mount Shasta City area tonight through Wednesday afternoon.
  Heaviest snow impacts are expected into Siskiyou County,
  especially for the Mount Shasta area and higher passes in
  western/southern Siskiyou Co. Heavy, wet snow in the Mount Shasta
  area will likely have snowfall rates an inch per hour, and the
  high res HREF is suggesting that it's more likely (70-90% chance)
  to reach over 2 and up to 3 inches per hour late this evening into
  Wednesday morning, when conditions are expected to be the worst.
  Current forecasts call for 15 to 20 inches of storm total snowfall
  from near Weed southward to Mount Shasta City and around 6 inches
  at Dunsmuir. Snow levels will fluctuate though around 2000 to 3500
  feet this evening through Wednesday afternoon. So confidence is
  moderate on storm total snowfall totals for lower elevations near
  Mount Shasta. The combination of heavy snow and wind are likely
  lead to down trees and power outages as well as impassible roads,
  low visibilities and white out driving conditions at times. Above
  3500 feet in western/southern/southeastern Siskiyou County, very
  heavy snow and strong gusty winds are likely to create high
  impacts from heavy snowfall around 20 to 30 inches (but locally
  higher over higher mountains) and low visibilities. Across the
  Southern Oregon Cascades and Siskiyous, also expect heavy snow
  with snowfall totals ranging from around 8 to 18 inches and
  locally up to 2 feet. Exposed higher mountains will also see a
  potential for strong winds and white out conditions at times,
  especially Tuesday evening into Wednesday morning. East of the
  Cascades, expect areas of moderate to heavy snow along with strong
  gusty winds. This will bring impacts to much of the area with
  heaviest snow expected north of Chiloquin over northern Klamath
  County. Travelers are urged to avoid travel during the worst of
  the storm and for these hard hit areas, and not take any detours
  during time of winter storms. Please see the WSWMFR for details.

There's fairly good agreement the core of the heavier precipitation
will shift south into Northern Cal during the day Wednesday with
light to occasionally moderate precipitation along the Oregon
coast and coastal mountains, before shifting north over southwest
Oregon again on Thursday. Snow levels by this time will increase
and will above all the pass levels by Thursday afternoon.

All signs are pointing towards a continued active pattern into
next weekend. There's some evidence showing another developing
surface low moving inside of 130W late Thursday night into Friday
morning which could bring the potential for moderate to strong
winds at the coast, moderate to heavy precipitation along the
coast, coastal mountains, and the Mount Shasta area. Snow levels
will start out around 8,000 feet around the Mount Shasta Area
which will limit snowfall to Mount Shasta, with no impacts
expected along highway 89 and the I-5 corridor. Upper troughing
will remain over the area this weekend, but at this time were not
expecting any significant impacts.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning from 4 PM this afternoon to 4 PM PST
     Wednesday for ORZ027-028-030.

     High Wind Warning from 1 PM this afternoon to 1 PM PST Wednesday
     for ORZ021-022-029>031.

     Winter Weather Advisory from 4 PM this afternoon to 4 PM PST
     Wednesday for ORZ027>030.

     High Surf Warning until 4 PM PST Wednesday for ORZ021-022.

     Wind Advisory from 1 PM this afternoon to 7 AM PST Wednesday for
     ORZ023>026.

CA...Winter Storm Warning from 4 PM this afternoon to 4 PM PST
     Wednesday for CAZ080>083.

     High Wind Warning from 1 PM this afternoon to 1 PM PST Wednesday
     for CAZ081-084-085.

     Winter Weather Advisory from 4 PM this afternoon to 4 PM PST
     Wednesday for CAZ085.

PACIFIC COASTAL WATERS...Small Craft Advisory until 10 AM PST this
     morning for PZZ350-356-370-376.

     Hurricane Force Wind Warning until 7 AM PST Wednesday for PZZ350-
     356-370-376.

&&

CC