High Wind in Oregon, November 10 to 11, 2024

Area Forecast Discussion
National Weather Service Medford OR
1005 PM PST Sun Nov 10 2024

...Updated AVIATION discussion...

.DISCUSSION...An update is not necessary this evening, with our
week of active weather underway and appropriately advertised at
this juncture. Please see the previous discussion below for all of
the details.

A seasonably strong/wet cold front is about to reach the coast,
and will continue east across the area overnight through
Monday/Veterans Day. A surface trough will follow closely behind
with additional showers and snow showers in a colder air mass
Monday afternoon into Tuesday morning. A Winter Weather Advisory
remains in effect above 5000 feet for the southern Oregon
Cascades from early Monday morning through Tuesday morning with 8
to 16 inches expected and southwest to west wind gusts up to 50
mph. This includes the Crater Lake, Diamond Lake, and Willamette
Pass areas, with the heaviest snow during Monday morning and late
Monday afternoon through the evening. With the westerly flow, snow
will be mainly in the Cascades, from the Dead Indian Memorial
Highway and Lake of the Woods area northward. Snow levels are
expected to bottom at around 4500 feet, with a modest accumulation
of a few inches between 4500 and 5000 feet. Snow amounts will be
much lighter on the east side, mainly less than an inch.

Also, a High Surf Advisory remains in effect for southern Oregon
beaches from 10 PM PST Monday evening to 10 PM PST Tuesday
evening. Otherwise, Tuesday will be a relative break in the
weather with a weak warm front producing light rain, mainly near
the coast, and mixed light rain and snow for the southern Oregon
Cascades into northern Klamath County.

The main event looks to be late Tuesday night into at least early
Thursday morning with an atmospheric river focusing a total of 2
to 5 inches of rain on Curry County, with around 2 inches forecast
for Coos and western Siskiyou counties, a half inch to 2 inches
of precipitation elsewhere on the west side (including the
Cascades), and up to three quarters of an inch on the east side.
It will also be windy over much of the area with a High Wind Watch
in effect for the coast Tuesday evening into Wednesday morning,
and a high probability for south to southwest winds solidly at
Advisory strength in the Shasta Valley and east of the Cascades
during Wednesday into Wednesday night. Also of note, the strong
southerly flow should bring lowering snow levels to 4000 to 4500
feet in the Mt. Shasta area (including Snowmans Sumit) during
Wednesday afternoon and night.

There is uncertainty in strength and in which areas will be
favored to receive additional showers and snow showers later
Thursday into Friday night.

The highest probability is for a break in the action Saturday
ahead of another wet system Saturday night into early next week.

&&

.AVIATION...11/06Z TAFS...VFR ceilings continue across northern
California and southern Oregon, with rainfall bringing occasional of
MVFR and IFR visibility over North Bend. A cold front will move
eastward through the day, bringing widespread showers. Snow levels
of 4500-500 feet will support snow showers over the Cascades and
east side terrain. Periods of locally lower ceilings and
visibilities will be possible over inland areas under rain and show
showers, and terrain may be obscured. Additionally, gusty winds are
expected over higher terrain east of the Cascades through this
evening.

Wind shear also remains in area guidance over the Oregon coast and
elevated terrain, with winds at 2000 feet out of the south at 40 to
50 knots. Shear is expected to decrease along the coast early this
morning, with improvement across the area by this afternoon.

A second weaker front could bring additional rainfall along the
Oregon coast and over the Cascades towards the end of the TAF
period. -TAD

&&

.MARINE...Updated 900 PM PST Sunday, November 10, 2024...

Southerly winds continue to increase tonight and wind gusts up to
40 knots are likely, especially north of Cape Blanco. The front
should move through the waters by Monday morning and a high long
period swell will fill in the front's wake. This swell will linger
in the waters on Tuesday. Winds will peak Tuesday night to near
45 kt sustained and 55 kt gust and there is a 70-80% probability
of storm force winds in the southern Oregon waters during this
time. It is highly probable that a Storm Warning will be issued
tomorrow morning covering the period from 06Z Wednesday (10 PM PST
Tuesday night) to 15Z (7 AM PST) Wednesday morning. After, seas
will lower a few feet on Wednesday and Thursday. Even when the
swell lowers, it will be hazardous to smaller crafts with wave
heights around 17 feet and a wave period around 13 seconds.

-Smith/Hermansen

&&

.BEACH HAZARDS...Updated 230 PM PST Sunday, November 10, 2024...

Model guidance has been consistently showing NW swells arriving
following the front later tonight into Monday. Seas briefly subside
immediately behind the front Monday (6 hours or so during the
morning), but then build significantly Monday afternoon and Monday
night, reaching a peak of 17-21 feet, 16 seconds by early Tuesday
morning. This will bring large breaking waves (22-26 feet) to the
beaches and coastline through Tuesday afternoon. Seas will gradually
subside Tuesday night. A high surf advisory has been issued for 10
PM Monday through 10 PM Tuesday because of these dangerous surf
conditions.

The next system will bring stronger winds, and these will peak
Tuesday night to near 45 kt sustained and 55 kt gusts. These
conditions bring a 70-80% probability of storm force winds in the
southern Oregon waters during this time. A High Surf Warning will
likely be issued tomorrow morning for the Tuesday night risk because
the waves with the strong winds will impact southern Oregon beaches,
especially from Port Orford south.

Large breaking waves create hazardous conditions along and within
the surf zone, and could inundate beaches and low lying shorelines.
If you have plans to venture out to the beaches early-mid next week,
pay close attention to the ocean, stay away from the surf zone and
off of jetties. Also, keep checking back for forecast updates.
-BPN/Hermansen

&&

.PREV DISCUSSION...  /Issued 225 PM PST Sun Nov 10 2024/

SHORT TERM (Tonight through Tuesday)...Light showery
precipitation continues across much of the area this afternoon as
a warm front passes across through the region. Rainfall will
remain light through this evening, and little impacts are
expected, especially with snow levels rising to above 7000 feet.
Despite the rather quiet situation today, busy, impactful weather
is in store for us over the next several days.

The first significant event will begin this evening as a strong
cold front approaches the forecast area. Models continue to show
widespread moderate to locally heavy precipitation spreading into
the area overnight and into Monday morning. The heaviest
precipitation is expected along the coast and coastal mountains,
where 1 to 2 inches of rain is forecast through Monday afternoon.
Inland, moderate to locally heavy precipitation (generally 0.25 to
1.0 inches) is likely from the Cascades west. Then, light to
moderate precipitation (generally 0.10 to 0.50 inches) is expected
east of the Cascades. Additional light to moderate precipitation
in widespread showers are expected behind the passage of the front
as the upper trough passes overhead Monday night, followed by a
warm front Tuesday. A thunderstorm or two is even possible west of
I-5 through Monday afternoon into night.

Snow impacts are expected in the Cascades with this front
Sunday night and Monday, as well as in showers behind the front
Monday evening through Tuesday morning. Snow levels will begin
around 7500 feet but quickly lower to 4500 to 5000 feet with and
behind the frontal passage. This is likely to bring snow to the
higher passes in the Cascades on Monday, with moderate snow
impacts above 5000 feet elevation north of highway 140. Current
forecasts support 3 to 7 inches of snow falling above 5000 ft
elevation during the day Monday. Lighter snow impacts are expected
elsewhere on Monday for areas from Highway 140 south in the
Cascades and across higher mountains east of the Cascades and
Siskiyous south. Behind the front, a colder and wet pattern sets
up Monday evening through Tuesday as the upper trough moves into
the region. Moist onshore flow and upper level support allow for
continued, widespread showers, with greatest activity along and
west of the Southern Oregon Cascades. Snow levels are forecast to
be down to around 4500 feet and locally to 4000 feet. The National
Blend of Models supports additional moderate snow affecting areas
above 5000 feet north of Highway 140 (with an additional 3 to 7
inches falling). A winter weather advisory is in effect for
portions of the Southern Oregon Cascades above 5000 feet elevation
(north of Highway 140) Sunday night through Tuesday morning.
Please see the WSWMFR for details. Light snow impacts, with
snowfall totals of 1 to 3 inches are expected in showers down to
around 4500 feet in the Cascades, including for areas near and
south of Highway 140, and for areas east of the Cascades along
Highway 97 north of Chiloquin. For other mountains and higher
terrain above 4500 feet, expect mainly light snow with showers.

Additionally, ahead of the front, gusty south to southwest winds
are expected as a 45 to 55 kt mid level, 700 mb, jet moves
overhead. This is expected to bring advisory level winds (gusting
to 45 to 50 mph) into the Shasta Valley and higher terrain east of
the Cascades tonight into Monday. A wind advisory remains in
effect for these areas. Please see the NPWMFR for details. Gusty
south winds are also likely over exposed higher mountains and
along the coast ahead of this frontal passage. Along the coast,
winds are expected to peak Sunday evening and night, with
winds gusting up to 50 mph. For inland areas, winds are expected
to peak Sunday night into Monday morning.

Showers will taper off through Tuesday, but will not quite come to
an end before another strong storm arrives.

LONG TERM...Tuesday Night through Saturday, Nov 12-16...

The midweek storm will be the strongest of the two events, and
will be the strongest storm so far this season. A large upper
level trough originating from the western Aleutians will
deepen as it quickly approaches the Pacific Northwest by Tuesday
night. The surface low will remain well to the north, eventually
passing onshore near Vancouver Island late Wednesday, but not
before pushing a strong cold front trough southern Oregon and
northern California.

The first concern with this system is rain. The leading edge of
precipitation should pass over the coast overnight Tuesday night,
with rain spreading west to the Cascades by midday, then to the East
Side through the afternoon. With IVT values of between 500 and 750,
moisture inflow will be strong, however, much of that is due to the
stronger winds associated with the system (more on that below). What
is important is the direction of the prevailing flow, which in this
case, will be out of the southwest. This will provide good upslope
mechanics along the coastal ranges, the Cascades, and the Siskiyous,
and especially in the Brookings area. These are where the heaviest
rainfall amounts will be, between 2 to 4 inches, although totals
will not be altogether unusual for systems like these and during
this time of year. That wind direction will, however, also
produce downslope flow in the Rogue Valley and east of the
Cascades. Rainfall totals here were reduced a bit, down to around
or below half an inch, but we still expect a good precipitation
event for all of the forecast area. Overall, rainfall amounts will
be healthy, but given the low river levels, no major flooding is
expected. Nuisance flooding is possible, such as small creeks and
streams, ditches blocked by debris or fallen leaves, or in poorly
drained urban areas.

Winds will also be a concern, with this storm likely producing
the strongest winds we've seen so far this season. Forecast
surface pressure gradients along the coast between Arcata and
North Bend range from -9 to -10mb, while gradients between
Redding and Medford range from -8 to -9mb. Meanwhile, model
solutions are suggesting 60 to 70 kt winds at 700 mb. With all of
this in mind, it is likely that Wind Advisories and Warnings will
be necessary, especially along the coast and across the East Side.
Wind advisories may also be necessary in the Shasta Valley and
the Rogue Valley near Ashland, but the prevailing southwest flow
will not align well with the valleys, so these areas will be
mainly gradient driven and therefore a bit weaker than otherwise.
Winds at the coast will peak Wednesday afternoon, with inland
areas peaking into the evening and overnight. A High Wind Watch
has been issued for the coast Tuesday evening into Tuesday night,
where wind gusts will be strongest, possibly peaking as high as 70
mph at headlands and along exposed portions of Highway 101.

The final, but lesser concern is snow. With the southwest flow
tapping into warmer air to the south of us, snow levels will be a
bit on the high side, beginning the event at around 6000 feet,
then only dropping to around 4500 to 5000 feet after the front
passes, when precipitation has likely transitioned to a more
showery regime. This will keep snow from being a major impact, but
heavier showers, or the very last edge of the frontal
precipitation, could produce just enough snow at the higher
Cascade passes (around and above 5000 feet) to cause some travel
difficulties. We are watching the Mount Shasta and McCloud area
for the possibility of lower snow levels, which we can typically
see during events like these. With the prevailing winds out of the
southwest, upslope precipitation production will not be as
strong, so at this time we do not expect precipitation rates to be
heavy enough to drag snow levels down to the elevation of I-5
near Mount Shasta, at least not for any significant amount of
time. It does appear snow levels will lower to Snowman Summit just
west of McCloud, so heavy wet snow could produce travel impacts
along highway 89 during the day Wednesday.

Interests in all of the areas mentioned above should begin
preparations now for strong winds and heavy rain. Keep up to date
with the latest forecast updates, especially as additional
Warnings and Advisories are issued over the next several shifts.
Also, please see the marine and beach hazards sections of this
discussion below for more information on hazards not mentioned so
far.

Once the front passes through the area (exiting by Thursday
morning), the system slows, keeping upper level troughing overhead
through Friday night. Temperatures will cool to about 5 to 10
degrees below normal as the cold air settles into the region.
Along with ongoing onshore flow, precipitation chances will
continue through this time, with snow levels hovering between 3000
and 4000 feet. There will not be continuous precipitation, as the
NBM suggests with near continual high PoPs, but instead we expect
hit-or- miss and off-again-on-again showers will be the rule
Thursday and Friday. Precipitation amounts will vary greatly from
place to place, and some showers may be strong enough to produce
graupel or very small hail.

Saturday, the trough shifts just far enough to the south and east
to allow ridging to nudge in from the west, producing a drying
trend for much of the region. The reprieve may be short, however,
as model solutions are showing the possibility of another frontal
system arriving on Sunday. -BPN/CC

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 7 AM PST Monday for ORZ030-031.

     High Surf Advisory from 10 PM Monday to 10 PM PST Tuesday for
     ORZ021-022.

     High Wind Watch from Tuesday afternoon through Wednesday morning
     for ORZ021-022.

     Winter Weather Advisory from 4 AM Monday to 10 AM PST Tuesday
     for ORZ027-028.

CA...Wind Advisory until 7 AM PST Monday for CAZ081-085.

PACIFIC COASTAL WATERS...High Surf Advisory from 10 PM Monday to 10
     PM PST Tuesday for PZZ350-356.

     Gale Warning until 10 AM PST Monday for PZZ350-356-370-376.

     Hazardous Seas Warning from 10 AM Monday to 4 PM PST Tuesday for
     PZZ350-356-370-376.

&&