NWS Medford, OR wrote its last area forecast discussion before the first event at Nov 19, 2:40 PM PST, 1 hour 20 minutes earlier.
Area forecast discussion, Nov 19, 2:40 PM PST, 1 hour 20 minutes before
Area Forecast Discussion...CORRECTED
National Weather Service Medford OR
240 PM PST Tue Nov 19 2024
...Corrected Long Term Discussion...
.SHORT TERM...A bomb cyclone is located off the coast of northern
Oregon and southern Washington. Surface analysis from WPC
indicates this low has deepened to around 955 mb (per analysis at
18z) and models are forecasting the low deepen further to around
941 mb this afternoon. This rapidly deepening low and strong front
will bring dangerous impacts to the coast due to high winds, high
surf and heavy rain. High impacts are expected inland as well due
to strong winds and heavy snow, especially over the mountains
into Siskiyou County and for areas east of the Cascades. Impacts
are expected to peak along the coast late this afternoon inland
tonight, and peak inland this evening into Wednesday. This is an
unusually strong storm to impact the area. (The last time we have
issued a hurricane force wind warning for the coastal waters was
October 2016.) Power outages are possible in areas with high winds
and heavy snow/strong winds. Roads may become impassible due to
heavy snow and low visibilities. Impacts are expected for higher
passes (including I-5 Siskiyou Summit, Highway 140 Lake of the
Woods, Diamond Lake area, and Sawyers Bar road in western
Siskiyou), portions of highway 97 (north of Chiloquin). Major
impacts are expected for the Mount Shasta area (including
Interstate 5 near Mount Shasta and Highway 89 east of Mount
Shasta) due to heavy snow and strong winds. Residents are urged to
prepare for potential of extended power outages and travels are
urged to avoid travel, especially in the hardest hit areas.
* WINDS: Winds have increased early this afternoon with gusts of
around 54 mph at Buoy 15 off Cape Blanco and gusts of 61 mph at
Port Orford. These winds will peak (with gusts up to 70 mph but
locally up to 85 mph) late this afternoon into tonight along the
coast. Inland, for areas west of the Cascades winds have
increased to 65 mph over the Siskiyou Mountains and to around 56
mph in the southern Shasta Valley. These winds will continue to
increase, peaking (gusts 40 to 60 mph in valleys west of the
Cascades in Oregon and higher over the mountains) this evening
through early Wednesday morning and peaking this evening through
Wednesday morning in the Shasta Valley. East of the Cascades
winds have begun to increase this afternoon with winds gusting
to around 30 to 45 mph. These winds will increase further and
peak (gusts to around 60 mph) tonight into Wednesday afternoon.
* 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.
* 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 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: As this atmospheric river brings a strong stream of
moisture into the area, heavy precipitation is expected 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, including over the
mountains/higher terrain and Mt Shasta City area. Additional
rain is expected Thursday into Friday as another system arrives
with higher snow levels. With the heavy precipitation, rapid
rises in rivers and small streams are expected. Current guidance
brings the Coquille River to just below action stage/bankfull.
Small streams have the potential for flood, especially along the
coast and into southwest Josephine County and western Siskiyou
County. A flood watch (FFAMFR) is in effect for these areas.
Elsewhere, west of the Cascades we are monitoring conditions for
the potential for flooding. Please see the ESFMFR for details.
* SNOWFALL: Heavy snow is expected to impact the mountains
(Cascades, Siskiyous and mountains in Western Siskiyou Co.) and
the Mount Shasta City area late today through Wednesday
afternoon. Observations indicate moderate snow and low
visibilities have already begun in the Mount Shasta City area
and light to moderate snow over higher passes. 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 likely (60-90% 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 around6 inches at
Dunsmuir. Snow levels will fluctuate though around 2000 to 3500
feet today through Wednesday afternoon. Confidence is high for
snowfall occuring but moderate on exact 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.
* Precipitation continues Wednesday night but he focus for heavy
precipitation will shift slightly southward into Northern
California. Snow levels will be rising during this time. Expect
some continuing impacts from snow above 4000 to 5000 feet
elevation across Siskiyou County Wednesday evening and night
then models support higher snow levels (6000 feet and higher)
early Thursday.
.LONG TERM (Thursday through Monday)...
Overview:
Precipitation will continue through the week, albeit lighter
amounts expected later in the week compared to earlier in the
week. Friday onward we really start to see lesser amounts unfold.
That said, might need a Winter Weather Advisory to account for
snowfall impacts starting Fri/Friday night, but this can wait
until we get past this first round of the atmospheric river
conditions currently impacting the PacNW. Could also see some
lingering flash flood potential Thursday through Friday morning,
especially areas in southwest Oregon and northwest California.
Another round of breezy to windy conditions expected Thursday
through Friday. Lastly, expecting seasonable temperatures through
the extended forecast period.
Further Details:
The parent 500mb closed low which is helping produce our strong
surface low currently impacting the coast today will wobble in the
same vicinity through the week. This will allow for a steady influx
of moisture from the Pacific. By Thursday, the parent low meandering
off the coast of Vancouver Island could kick out a strong rapidly
strengthening surface low. Given the pressure falls (upwards of 2mb
per hour) and resulting pressure gradient, this could bring another
round of strong wind speeds to the area. Current forecast speeds
could warrant a wind advisory and/or high wind warning if this trend
holds, mainly for coastal areas/ranges and some of the typical
windier spots on the eastside. The peak of these winds expected
Thursday night into Friday morning.
The trajectory of this system Thurs/Fri is southerly, and without
the orthogonal wind to the Cascades we will miss out on some upslope
component. This means snowfall amounts wont be as high with this
trajectory, but still looking at the potential for higher elevation
snowfall which could lead to an advisory. The QPF with this system
is notable, and while the snowfall will generally be advisory level,
rainfall amounts could be on the order of 4 to 5 inches in a 36 hour
period Thursday morning through Friday morning. This would primarily
be over southwest Oregon and northwest California where excessive
rainfall outlooks (from WPC) have been issued for flash flooding
potential. These areas can generally take a lot of rainfall;
however, recent rainfall has saturated the ground and additional
rainfall could cause problems during the morning/evening commute on
Thursday in addition to the evening commute. Friday onward,
rainfall/snowfall chances continue, but with much less QPF
involved.
-Guerrero
&&
.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
&&
.MARINE...Updated 200 PM PST Tuesday, November 19, 2024...Conditions
are rapidly deteriorating 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 a compact low pressure
deepens inside of 130 W late Thursday into Friday and tracks even
closer to the coast. 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 a strong potential for a round of southerly gales
or storm force winds 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. -BPN/BR-y
&&
.BEACH HAZARDS...Updated 200 PM 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
&&
.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 until 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 until 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 until 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...Hurricane Force Wind Warning until 4 AM PST
Wednesday for PZZ350-356-370-376.
Hazardous Seas Warning from 4 AM to 10 PM PST Wednesday for
PZZ350-356-370-376.
&&
CC