Hazardous Seas Warning 9, NWS Medford, OR

727 
WHUS76 KMFR 261015
MWWMFR

URGENT - MARINE WEATHER MESSAGE
National Weather Service Medford OR
215 AM PST Tue Jan 26 2021

PZZ350-356-370-376-262315-
/O.CON.KMFR.SC.Y.0013.000000T0000Z-210126T1500Z/
/O.CAN.KMFR.GL.W.0007.210126T1500Z-210126T1900Z/
/O.EXT.KMFR.SR.W.0004.210126T1500Z-210127T0100Z/
/O.CON.KMFR.SE.W.0009.210127T0100Z-210128T1000Z/
Coastal waters from Florence to Cape Blanco OR out 10 nm-
Coastal waters from Cape Blanco OR to Pt. St. George CA out 10 nm-
Waters from Florence to Cape Blanco OR from 10 to 60 nm-
Waters from Cape Blanco OR to Pt. St. George CA from 10 to 60 nm-
215 AM PST Tue Jan 26 2021

...SMALL CRAFT ADVISORY REMAINS IN EFFECT UNTIL 7 AM PST THIS
MORNING...
...STORM WARNING NOW IN EFFECT FROM 7 AM THIS MORNING TO 5 PM PST
THIS AFTERNOON...
...HAZARDOUS SEAS WARNING REMAINS IN EFFECT FROM 5 PM THIS
AFTERNOON TO 2 AM PST THURSDAY...

* WHAT...Northwest seas 15 feet at 15 seconds are occuring this
  morning. South winds 40 to 50 kt with gusts up to 60 kt and very
  steep wind-driven seas of 18 to 22 feet are expected by this 
  afternoon. 

* WHERE...All areas.

* WHEN...Winds and seas will increase rapidly this morning,
  reaching a peak this afternoon and early evening. Winds will
  weaken by tonight, but seas will remain steep and elevated into
  Wednesday. 

* IMPACTS...Very strong winds and very steep seas could capsize 
  or damage vessels. Visibilities will be significantly reduced.

* View the hazard area in detail at 
  https://www.wrh.noaa.gov/mfr/HAZARD

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Mariners should remain in port, alter course, and/or secure the
vessel for very strong winds and very steep and hazardous seas.

&&

$$

Visit us at https://www.weather.gov/Medford

573 
WHUS76 KMFR 261635
MWWMFR

URGENT - MARINE WEATHER MESSAGE
National Weather Service Medford OR
835 AM PST Tue Jan 26 2021

PZZ350-356-370-376-270545-
/O.CON.KMFR.SR.W.0004.000000T0000Z-210127T0100Z/
/O.CON.KMFR.SE.W.0009.210127T0100Z-210128T1000Z/
Coastal waters from Florence to Cape Blanco OR out 10 nm-
Coastal waters from Cape Blanco OR to Pt. St. George CA out 10 nm-
Waters from Florence to Cape Blanco OR from 10 to 60 nm-
Waters from Cape Blanco OR to Pt. St. George CA from 10 to 60 nm-
835 AM PST Tue Jan 26 2021

...STORM WARNING REMAINS IN EFFECT UNTIL 5 PM PST THIS
   AFTERNOON...
...HAZARDOUS SEAS WARNING REMAINS IN EFFECT FROM 5 PM THIS
   AFTERNOON TO 2 AM PST THURSDAY...

* WHAT...Northwest seas 15 feet at 15 seconds are occuring this 
  morning. South winds 40 to 50 kt with gusts up to 60 kt and 
  very steep wind-driven seas of 18 to 22 feet are expected by 
  this afternoon.

* WHERE...All areas.

* WHEN...Winds and seas will increase rapidly this morning, 
  reaching a peak this afternoon and early evening. Winds will 
  weaken by tonight, but seas will remain steep and elevated 
  into Wednesday.

* IMPACTS...Very strong winds and very steep seas could capsize 
  or damage vessels. Visibilities will be significantly reduced.

* View the hazard area in detail at 
  https://www.wrh.noaa.gov/mfr/HAZARD

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Mariners should remain in port, alter course, and/or secure the
vessel for very strong winds and very steep and hazardous seas.

&&

$$

Visit us at https://www.weather.gov/Medford

370 
WHUS76 KMFR 262258
MWWMFR

URGENT - MARINE WEATHER MESSAGE
National Weather Service Medford OR
258 PM PST Tue Jan 26 2021

PZZ350-356-370-376-271200-
/O.CON.KMFR.SR.W.0004.000000T0000Z-210127T0100Z/
/O.CON.KMFR.SE.W.0009.210127T0100Z-210128T1000Z/
Coastal waters from Florence to Cape Blanco OR out 10 nm-
Coastal waters from Cape Blanco OR to Pt. St. George CA out 10 nm-
Waters from Florence to Cape Blanco OR from 10 to 60 nm-
Waters from Cape Blanco OR to Pt. St. George CA from 10 to 60 nm-
258 PM PST Tue Jan 26 2021

...STORM WARNING REMAINS IN EFFECT UNTIL 5 PM PST THIS
AFTERNOON...
...HAZARDOUS SEAS WARNING REMAINS IN EFFECT UNTIL 2 AM PST
THURSDAY...

* WHAT...South winds 40 to 50 kt with gusts up to 60 kt and very
  steep wind-driven seas of 18 to 22 feet are expected by this
  afternoon. Seas will remain high behind the  front, diminishing
  to 13 to 15 feet, then rising again to 17 to 19 feet with a 
  chaotic mix of northwest swell at 9 to 15 feet, and southerly 
  wind waves with south winds of 20 to 30 kt.

* WHERE...All areas.

* WHEN...Winds will weaken by tonight, but seas will remain steep
  and elevated into Wednesday. 

* IMPACTS...Very strong winds and very steep seas could capsize 
  or damage vessels. Visibilities will be significantly reduced.

* View the hazard area in detail at 
  https://www.wrh.noaa.gov/mfr/HAZARD

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Mariners should remain in port, alter course, and/or secure the
vessel for very strong winds and very steep and hazardous seas.

&&

$$

Visit us at https://www.weather.gov/Medford

145 
WHUS76 KMFR 270403
MWWMFR

URGENT - MARINE WEATHER MESSAGE
National Weather Service Medford OR
803 PM PST Tue Jan 26 2021

PZZ350-356-370-376-271715-
/O.CON.KMFR.SE.W.0009.000000T0000Z-210128T1000Z/
Coastal waters from Florence to Cape Blanco OR out 10 nm-
Coastal waters from Cape Blanco OR to Pt. St. George CA out 10 nm-
Waters from Florence to Cape Blanco OR from 10 to 60 nm-
Waters from Cape Blanco OR to Pt. St. George CA from 10 to 60 nm-
803 PM PST Tue Jan 26 2021

...HAZARDOUS SEAS WARNING REMAINS IN EFFECT UNTIL 2 AM PST
THURSDAY...

* WHAT...South to southwest winds 15 to 25 kt through tonight,
  becoming southeast and increasing to 25 to 30 kt by early
  Wednesday morning. Very steep and hazardous seas 14 to 19 ft at
  13 to 15 seconds.

* WHERE...All areas.

* WHEN...Until 2 AM PST Thursday.

* IMPACTS...Very steep and hazardous seas could capsize or damage
  vessels. Bar crossings will become treacherous.

* View the hazard area in detail at 
  https://www.wrh.noaa.gov/mfr/HAZARD

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Recreational boaters should remain in port. Commercial vessels
should prepare for very steep seas and consider remaining in port
until conditions improve.

&&

$$

Visit us at https://www.weather.gov/Medford

820 
WHUS76 KMFR 271001
MWWMFR

URGENT - MARINE WEATHER MESSAGE
National Weather Service Medford OR
201 AM PST Wed Jan 27 2021

PZZ350-356-370-376-272315-
/O.CON.KMFR.SE.W.0009.000000T0000Z-210128T1000Z/
Coastal waters from Florence to Cape Blanco OR out 10 nm-
Coastal waters from Cape Blanco OR to Pt. St. George CA out 10 nm-
Waters from Florence to Cape Blanco OR from 10 to 60 nm-
Waters from Cape Blanco OR to Pt. St. George CA from 10 to 60 nm-
201 AM PST Wed Jan 27 2021

...HAZARDOUS SEAS WARNING REMAINS IN EFFECT UNTIL 2 AM PST
THURSDAY...

* WHAT...South winds 25 to 30 kt. Very steep and hazardous seas 15
  to 18 ft at 14 seconds.

* WHERE...All areas.

* WHEN...Until 2 AM PST Thursday.

* IMPACTS...Very steep and hazardous seas could capsize or 
  damage vessels. Bar crossings will become treacherous.

* View the hazard area in detail at 
  https://www.wrh.noaa.gov/mfr/HAZARD

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Recreational boaters should remain in port. Commercial vessels
should prepare for very steep seas and consider remaining in port
until conditions improve.

&&

$$

Visit us at https://www.weather.gov/Medford

327 
WHUS76 KMFR 272218
MWWMFR

URGENT - MARINE WEATHER MESSAGE
National Weather Service Medford OR
218 PM PST Wed Jan 27 2021

PZZ350-356-370-376-281130-
/O.EXT.KMFR.SE.W.0009.000000T0000Z-210128T0600Z/
/O.NEW.KMFR.SC.Y.0015.210128T0600Z-210129T0600Z/
Coastal waters from Florence to Cape Blanco OR out 10 nm-
Coastal waters from Cape Blanco OR to Pt. St. George CA out 10 nm-
Waters from Florence to Cape Blanco OR from 10 to 60 nm-
Waters from Cape Blanco OR to Pt. St. George CA from 10 to 60 nm-
218 PM PST Wed Jan 27 2021

...HAZARDOUS SEAS WARNING NOW IN EFFECT UNTIL 10 PM PST THIS
EVENING...
...SMALL CRAFT ADVISORY IN EFFECT FROM 10 PM THIS EVENING TO
10 PM PST THURSDAY...

* WHAT...For the Hazardous Seas Warning, very steep and 
  hazardous seas 14 to 19 ft at 16 seconds. For the Small Craft 
  Advisory, seas 10 to 15 ft at 15 seconds expected.

* WHERE...All areas.

* WHEN...For the Hazardous Seas Warning, until 10 PM PST this 
  evening. For the Small Craft Advisory, from 10 PM this evening 
  to 10 PM PST Thursday.

* IMPACTS...Very steep and hazardous seas could capsize or 
  damage vessels. Bar crossings will become especially 
  treacherous.

* View the hazard area in detail at 
  https://www.wrh.noaa.gov/mfr/HAZARD

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Recreational boaters should remain in port. Commercial vessels
should prepare for very steep seas and consider remaining in port
until conditions improve.

&&

$$

Visit us at https://www.weather.gov/Medford

094 
WHUS76 KMFR 280346
MWWMFR

URGENT - MARINE WEATHER MESSAGE
National Weather Service Medford OR
746 PM PST Wed Jan 27 2021

PZZ350-356-370-376-281700-
/O.CON.KMFR.SE.W.0009.000000T0000Z-210128T0600Z/
/O.CON.KMFR.SC.Y.0015.210128T0600Z-210129T0600Z/
Coastal waters from Florence to Cape Blanco OR out 10 nm-
Coastal waters from Cape Blanco OR to Pt. St. George CA out 10 nm-
Waters from Florence to Cape Blanco OR from 10 to 60 nm-
Waters from Cape Blanco OR to Pt. St. George CA from 10 to 60 nm-
746 PM PST Wed Jan 27 2021

...HAZARDOUS SEAS WARNING REMAINS IN EFFECT UNTIL 10 PM PST THIS
EVENING...
...SMALL CRAFT ADVISORY REMAINS IN EFFECT FROM 10 PM THIS EVENING
TO 10 PM PST THURSDAY...

* WHAT...South to southwest winds 20 to 30 kt through this
  evening, becoming northwest and easting to 10 to 15 kt
  overnight. Very steep and hazardous seas of 14 to 18 ft peaking
  this evening, subsiding to 10 to 15 ft overnight and remaining
  steep through Thursday evening. 

* WHERE...All areas.

* WHEN...For the Hazardous Seas Warning, until 10 PM PST this 
  evening. For the Small Craft Advisory, from 10 PM this evening 
  to 10 PM PST Thursday.

* IMPACTS...Very steep and hazardous seas could capsize or 
  damage vessels. Bar crossings will become especially 
  treacherous.

* View the hazard area in detail at 
  https://www.wrh.noaa.gov/mfr/HAZARD

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Recreational boaters should remain in port. Commercial vessels
should prepare for very steep seas and consider remaining in port
until conditions improve.

&&

$$

Visit us at https://www.weather.gov/Medford

Area Forecast Discussion
National Weather Service Medford OR
256 PM PST Mon Jan 25 2021

.SHORT TERM...With a shortwave upper trough in place, scattered
showers are continuing today from the Cascades west. Showers will
linger through evening with snow levels near 2000 feet, then
diminish tonight. The break in the activity will be very brief.
Models remain on track showing a strong and moist, cold low
pressure system dropping out of the Gulf of Alaska tonight,
shifting south just off the Pacific Northwest coast. This will be
a significant weather system with impacts from heavy snow across
much of Siskiyou and portions of eastern Curry and Josephine
Counties (heaviest for 1500 feet elevation and above). Strong,
gusty winds are expected over the mountains, in the Shasta Valley
and at coastal headlands.

On Tuesday, models are on track, showing good agreement with a
997 mb surface low moving south of the coast of Washington and
Oregon. As this low nears the area, it will bring a front into the
coast Tuesday afternoon. Then as the surface low moves southward
just off the southern Oregon and northern California coast, this
front will shift inland and gradually to the southeast Tuesday
evening and night. This system will bring significant impacts with
moderate to heavy snow over portions of southwest Oregon and
northwest California along with some locations seeing strong,
gusty winds.

A strong mid level jet associated with this low pressure system
will move into the area. Models show 700 mb winds of 60 to 75 kt
out of the southwest moving into the area Tuesday afternoon and
evening. At the surface, a strong pressure gradient will develop
(9-11 mb from Medford to Redding) which will allow strong south
winds to develop in the Shasta Valley with gusts to around 60 to
70 mph. Gusty winds are also likely in the Rogue Valley,
especially south of Medford to Ashland, with gusts of around 35 to
45 mph. Gusty winds are likely from the Cascades east as well with
winds of 30 to 45 mph in the valleys and 45 to 60 mph over the
ridges. In the Rogue Valley, these winds may be accompanied by a
rain/snow mix or snow at times, especially Tuesday evening into
Tuesday night for areas above 1500 feet elevation. A wind
advisory is in place for the Summer Lake area in Lake County late
Tuesday afternoon through early Wednesday morning (Please see the
NPWMFR for details).

With this storm system, heavy precipitation rates will develop in
Curry, Josephine and Siskiyou counties late Tuesday afternoon
into Tuesday night. This combined with a cold air mass in place
will result in heavy, wet snow developing across these area. There
is high confidence for very heavy, wet snow in the Mount Shasta
area where strong upslope southerly winds will combine with
moisture. Heavy snow rates of up to 1 to 2 inches per hour are
expected at times, especially late Tuesday afternoon into
Wednesday morning. Total snow accumulations of 2 feet or more is
expected in the south central and southeast Sikiyou County area
near Mount Shasta from Tuesday afternoon through Wednesday
afternoon. Heavy snow rates are expected to extend into the
southern Shasta Valley as well where heavy snowfall combined with
strong winds (gusting to 60 to 70 mph) will bring blizzard-like
conditions at times with near zero visibility. This will make
roads impassible at times. Moderate to heavy snowfall will then
continue Wednesday morning into Wednesday afternoon for these
areas in Siskiyou County. A winter storm warning is in effect for
this area. This is a very dangerous situation and travelers are
urged to make plans to avoid travel during winter storm
conditions.

Other areas will also snow impacts. Across western Siskiyou,
Josephine and eastern Curry Counties models indicate moderate to heavy
snow is expected, with heaviest snow expected above 1500 feet
elevation and lighter snow amounts down to lower valley floors.
Although not as heavy or as long of a duration an event compared
to the snow in the Mount Shasta area, the lower passes and valley
locations (above 1500 feet) are expected to see a period of heavy
snow rates as this front moves inland. Elsewhere across the CWA,
areas of light to moderate snow are expected, including in western
valleys above 1500 feet, over the mountains and for areas from
the Cascades east. Heaviest snowfall is expected Tuesday evening
through early Wednesday morning for these areas. Please see the
WSWMFR for details on the snow and blowing snow expected in the
area Tuesday into Wednesday.

On Wednesday,the front will shift southeast of the area. However
the surface low off the coast of southern Oregon and far northern
California, will remain in place, gradually moving northward along
the coast Wednesday evening and night. With this low in place,
expect additional moderate to locally heavy precipitation across
southwest portions of the CWA, heaviest in Curry and Siskiyou
Counties and possibly into southern Josephine County. This will
bring continued impacts from snow for these areas through
Wednesday morning (and through Wednesday afternoon for the Mount
Shasta area).

Confidence is low in how much snow the lower west side valleys
may see Tuesday night into Wednesday morning due to uncertainty in
how much precipitation will occur and how widespread showers will
be. Snow levels are expected to lower down to between 500 to 1000
feet during this time. However, precipitation may remain light
across western valleys during this time. Precipitation may
increase in the afternoon on Wednesday across Josephine County.
However, snow levels are expected to rise to 2000 ft or higher at
that time. Wednesday evening and night, an upper low will move
down the Pacific Northwest coast with a weak surface low along the
coast. This pattern may bring continued moderate precipitation,
especially across Siskiyou County. This may result in additional
snow impacts, especially in the Mount Shasta area. We will need to
evaluate this will future model runs.

.LONG TERM...Wednesday evening until Tuesday morning

A deep and strong upper level low will remain off the Oregon coast
for at least another 18 to 24 hours from Wednesday into Thursday.
This system will continue to bring rain and snow to southern Oregon
and northern California adding to the snowfall totals from Tuesday
night and Wednesday. Right now, we're forecasting another 8 to 10
inches of snow Wednesday evening into Thursday around the Mt Shasta
City area. With snow levels around 3300 feet, confidence isn't high
in the forecast as slightly higher snow levels would drop those
totals.  It's unclear how much warmer air will be able to wrap up in
this low Wednesday evening into Thursday. In any case, the impacts
will be less compared to Tuesday night and early Wednesday because
the snowfall rates should be noticeably lower.

By late Thursday into early Friday, this low slowly starts to move
eastward yet lingers over Oregon.  There will be roughly a 20 to 30
percent chance for some lingering showers over the forecast area
from late Thursday into early Friday.  By midday Friday,  high
pressure will build briefly over the region.  However, the next
system will be arriving from the west by Friday evening and Friday
night.

Like the previous storm systems, this one will likely be
arriving from the north with a cooler airmass. However, ensembles
suggest this weekend storm system isn't as anomalously cold as the
storm on the 24th and the upcoming one on the 26th.  Snow levels
will likely be around 3500 feet.  We see little change in the snow
levels based on the distribution of the ensemble members this
weekend.

The other important feature of this storm is that it has some
important components of an atmospheric river.  About 66% percent of
the global ensemble forecast system(GEFS) members incorporate a
weak to moderate atmospheric river this weekend.  None of the GEFS
members show exceptionally high water vapor transport for this
weekend. Overall, impacts are not expected to be as high because the
potential for low level snow and flooding is low with the storm
system this weekend.

&&

.AVIATION...For the 25/18Z TAFs...Coastal showers continue this
morning with low snow levels persisting around 1500 to 2000 feet.
All TAF locations should remain in VFR throughout the day with a
stray shower moving by, especially closer to the coast.  Look for
LIFR ceilings tonight in the Umpqua Valley and a few of the valleys
west of the Cascades later tonight.  Otherwise, a strong low will
swing through the region Tuesday evening.  Although it's not in the
TAF forecast yet,  wind shear will be a concern late Tuesday
evening.

&&

.MARINE...Updated 200 PM PST Monday, 25 Jan 2021...Light showers and
a slight chance of thunderstorms will persist through this
afternoon. Gusty northwest winds ease this evening and overnight,
but very steep swell dominated seas will persist through this
afternoon. Seas remain elevated tonight, although a lengthening
dominant period allows them to transition from very steep into the
steep category.

This meager improvement will be short-lived. A strong cold front
arrives Tuesday morning with strong, widespread south gales and very
steep seas expected. This will lead to a period of occasional
storm force gusts Tuesday afternoon and evening. A Gale Warning
remains in effect for Tuesday. Winds ease late Tuesday with very
steep fresh swell remaining behind briefly.

South winds increase again Wednesday with the next front, although
winds will be much weaker than the Tuesday system and are only
expected to reach advisory levels. Seas build again Wednesday
afternoon, peaking around 14 to 16 ft. Conditions then improve
Thursday into Friday, with worsening conditions expected late Friday
into the weekend. -Sven

&&

.PREV DISCUSSION... /Issued 904 AM PST Mon Jan 25 2021/

SHORT TERM...Light showers continue today as an upper trough is
over the area. Showers are most concentrated along the coast
range with models favoring scattered showers spreading inland
across areas from the Cascades west this afternoon and evening.
Snow levels are low, around 1000 feet, this morning but will rise
to 2000 feet in the afternoon. Some light showers are possible
down to valley floors in western valleys this morning, then mainly
over elevations above 1500 to 2000 feet late this morning and
this afternoon. Any snow accumulations in showers are expected to
be mainly light. A brief break with mainly dry weather is expected
tonight.

Then a much stronger and moister low pressure system will
drop down from the north along the Pacific Northwest coast
Tuesday into Wednesday. This system will bring heavy snow to
portions of Siskiyou County and into Josephine County, mainly for
elevations above 1500 feet. The Mount Shasta area will see very
heavy snow impacts with 2 feet or more of snow expected from
Tuesday afternoon through Wednesday afternoon. Also moderate snow
is expected in the northern Shasta Valley, Jackson County, Douglas
County and across higher terrain from the Cascades east. Strong
winds are also expected in the southern Shasta Valley and Black
Butte area. These winds combined with snow may bring near zero
visibilities, including along Interstate 5, especially Tuesday
evening and night. This system will also bring strong, gusty south
winds to the coast on Tuesday afternoon into the early evening
with winds expected to gust to 60 mph over the coastal headlands
and gusts to 40 to 50 mph along the southern Coos and the Curry
coasts.

For details on this storm, please see the discussion below and the
winter warnings and advisories (WSWMFR).

AVIATION...For the 25/12Z TAFs...Showers continue this morning,
focused mainly west of I-5 and conditions are largely a mix of
MVFR/low end VFR from the Cascades westward. However, there are
areas of LIFR conditions in fog and low clouds in some of the deeper
valleys (Grants Pass, Klamath River Valley, portions of Umpqua
Basin). Showers will increase in coverage some this morning, mainly
west of the Cascades, then diminish later this afternoon. The lowest
conditions should improve by this afternoon and a MVFR/low end VFR
mix is expected to persist through this afternoon. Terrain
obscurations will continue into this evening, most common along
northwest facing slopes. Additional snow accumulations through
Monday will be light, mainly up to 2 inches over the higher terrain.
A stabilizing air mass on Monday night should lead to the formation
of valley IFR, especially west of the Cascades. -DW/BR-y

MARINE...Updated 200 AM PST Monday, 25 Jan 2021...Light showers and
a slight chance of thunderstorms will persist through this
afternoon. Gusty northwest winds ease this evening and overnight,
but very steep swell dominated seas will persist through this
afternoon. Combined west-northwest swell trains will transition from
14 ft at 11 seconds and 6 ft at 18 seconds this evening to 12 ft at
12 seconds and 8 ft at 15 seconds by Monday evening. Seas remain
elevated tonight, although a lengthening dominant period allows them
to transition from very steep into the steep category.

This meager improvement will be short-lived. A strong cold front
arrives Tuesday morning with strong, widespread south gales and very
steep seas expected. High resolution models are indicating the
potential for a strong coastal jet to develop Tuesday afternoon.
This will lead to the potential for a period of storm force gusts of
55 to 60 kt between 5 and 40 nm from shore Tuesday afternoon and
evening. A Gale Warning remains in effect for Tuesday and a Storm
Watch has been issued as well. Winds ease late Tuesday, however,
seas will remain very steep and elevated into Wednesday.

South winds increase again Wednesday with the next front, although
winds will be much weaker than the Tuesday system and are only
expected to reach advisory levels. Seas build again Wednesday
afternoon, peaking around 14 to 16 ft. Conditions then improve
Thursday into Friday, with worsening conditions expected late Friday
into the weekend. /BR-y

PREV DISCUSSION... /Issued 659 AM PST Mon Jan 25 2021/

DISCUSSION...Better late than never for this discussion, thanks
for your patience this busy morning waiting for this AFD. There
have been additional Advisories and Watches hoisted for this next
front anticipated to bring a prolonged period of high to very
high impact weather.

In the near term, moderate showers continue to move onshore
supported by orographic effects from the Coast range. Elevations
along and near the coast are likely to see these showers, which
could be locally and briefly intense through the morning. A
rain/snow mix, which could contain small hail or graupel, is
possible down to sea level, but snow accumulation levels should
generally be above 1kft. No CG lightning strokes or flashes have
been observed so far last night or this morning, but remains
possible for several more hours along the coast and over the
Pacific. We've got winter weather advisories out for areas along
and near the coast for tonight into the morning for these showers,
where 1 to 2 inches of new snow is likely. Showers have struggled
to stay intact east of I-5, but SPC HREF indicates that these
showers could make inland progress to the east portion of Jackson
County. As the cold pool continues to advance east this morning
past the Cascades, these showers will have an increasing chance
of staying intact and reinvigorating along the Cascades. The most
recent radar passes show this is already beginning to occur in
the Prospect and Butte Falls area.

The Winter Storm Warning was expanded in Josephine County. The
warning now includes areas above 1500 feet. This comes as the
expected tongue of warm air moves onshore more over northern
California, from Del Norte County south, than southern Oregon.
Snow levels are not expected to rise above 2000 feet on Tuesday,
allowing isolated heavier showers to drive the snow levels lower.
Current snow amounts call for between 2 and 3 inches of snow at
the Illinois valley floor and the NBM 24 hr snowfall
probabilities puts that likelihood at 65%-75%. There is a low
probability, 10%-25%, that heavier showers could cause higher
snowfall amounts to reach the 4 to 6 inch range, again per the NBM
24 hr snowfall probabilities.

The Winter Storm Warning for Central Siskiyou County was expanded
north along the west side of I-5. Areas east of I-5 between Hilt
and Grenada have been placed under an Advisory, both above and
below 3000 feet. The advisories are taking into account snow
produced from clouds but not from blowing snow. Winds will be
very strong in the Shasta Valley and along higher exposed terrain,
which could blow more snow into the area causing higher observed
amounts than predicted. These strong winds are backed by 700 mb
and 850 mb winds with a return interval of once in every five to
ten years per the NAEFS mean wind. These high winds also pose the
very real threat of creating blizzard conditions along I-5 between
Weed and Montague, and other areas of the Shasta Valley Tuesday
evening into Tuesday night. Please make alternative plans if
you're thinking of traveling through that area.

Hoisted Winter Weather Advisories for Douglas and Jackson Counties
above 1500 feet. Along with impactful snow amounts, strong
advisory level winds will be present Tuesday evening into Tuesday
night in the Rogue Valley between Medford and Siskiyou Summit,
including Ashland, as well as along other high, exposed terrain.
It will be possible that snow is observed down to the valley
floors, but confidence is not high regarding how much will stick.
Elevations between 1000 and 1500 feet may observe light
accumulations under one inch stick Tuesday evening, when the
heaviest precipitation is expected. Confidence is still very low
for snow sticking at the valley floor, but the colder 850 mb temps
and southwest flow during peak snowfall does indicate that it is
possible per climatology.

A Winter Weather Advisory was added for the Southern Oregon
Cascades and Siskiyou Mountains in Oregon. This includes route
138 and 230 intersection at Diamond Lake and the Mt. Ashland Ski
area. There is high confidence that along with 6-9 inches of snow,
with locally higher amounts up to one foot, that there will be
very strong wind gusts up to 60 mph Tuesday afternoon into the
night.

East of the Cascades, a Winter Weather Advisory above 4500 feet
was added. This includes route 97 north and south of Chemult,
route 140 at Warner Mountain Pass, route 395 south of Lake View
into Modoc County, CA where the advisory also includes portions of
routes 139 and 299 at Cedar Pass. Wind gusts in excess of 50 mph
are also expected for the same areas as the Winter Weather
Advisory. Along route 31 in Lake County from Silver Lake south to
Valley Falls a Wind Advisory was also introduced. 700 mb winds
will be from the southwest at 50 to 75 kts. This suggests that
wind gusts could reach the upper limit of the advisory (57 mph)
over higher elevations, while increasing confidence that lower
elevations along the roadway are likely to experience strong
gusts.

Winds along the coast, and especially at the headlands of Curry
County along highway 101, are forecast to be just under warning
criteria. KOTH-KACV pressure gradients are nearing the minimum
threshold of 8 mb to support warning level gusts per the GFS and
NAM-12. 850 mb winds per the NAM-12 are at 70-75 kts and could
easily support warning level gusts. Stay tuned with the forecast
over the coming day for any further developments. Strongest winds
along the coast are forecast for late Tuesday morning through the
afternoon.

In the long term, at day 8-10, snow levels per the NBM are
expected to be in the 3000-4000 feet range with another trough
bringing a wet front onshore Saturday through Sunday. These higher
snow levels and persistent wet pattern has caused a few rivers to
be projected to approach action stage near or shortly after the
first of the month. The rivers include the Coquille at a few
places, Deer Creek, and the Rogue and Illinois rivers. It can be
inferred that small creeks and streams will also be flowing
strongly at this time.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from noon Tuesday to 4 AM PST Wednesday
     for ORZ030-031.
     Wind Advisory from 1 PM Tuesday to 7 AM PST Wednesday for
     ORZ030-031.
     Winter Weather Advisory from 10 AM Tuesday to 10 AM PST
     Wednesday below 1500 feet in the for ORZ024.
     Winter Storm Warning from 10 AM Tuesday to 10 AM PST Wednesday
     above 1500 feet in the for ORZ024.
     Winter Weather Advisory from 10 AM Tuesday to 4 AM PST Wednesday
     above 1500 feet in the for ORZ023.
     Winter Weather Advisory from noon Tuesday to 4 AM PST Wednesday
     above 1500 feet in the for ORZ026.
     Winter Weather Advisory from noon Tuesday to 4 AM PST Wednesday
     for ORZ027-028.

CA...Winter Weather Advisory from noon Tuesday to 4 AM PST Wednesday
     for CAZ083-085.
     Winter Storm Warning from noon Tuesday to 4 PM PST Wednesday for
     CAZ081>083.
     Winter Weather Advisory from 10 AM Tuesday to 10 AM PST
     Wednesday below 1500 feet in the for CAZ080.
     Winter Storm Warning from 10 AM Tuesday to 10 AM PST Wednesday
     above 1500 feet in the for CAZ080.
     Winter Weather Advisory from noon Tuesday to 4 AM PST Wednesday
     for CAZ081.

Pacific Coastal Waters...Small Craft Advisory until 7 AM PST Tuesday for
     PZZ350-356-370-376.
     Small Craft Advisory from 10 PM Tuesday to 4 AM PST Thursday for
     PZZ350-356-370-376.
     Gale Warning from 7 AM to 10 PM PST Tuesday for
     PZZ350-356-370-376.
     Hazardous Seas Warning until 4 PM PST this afternoon for
     PZZ350-356-370-376.

CC/CC/CC