Ice Storm in Oregon, January 12 to 13, 2024

Area Forecast Discussion
National Weather Service Medford OR
403 PM PST Fri Jan 12 2024

Updated AVIATION Section

.DISCUSSION...Today through Sunday evening...Northwest flow is
bringing widespread cloud cover across northern California and
southern Oregon. With orographic lift as the main lifting
mechanism, precipitation will generally remain over Oregon coastal
ranges and the west side of the Cascades this evening.

An incoming cutoff low pressure system will bring more activity to
the area starting Saturday morning and continuing through the
weekend. Widespread precipitation will fall across the entire
coverage area through Sunday morning. West of the Cascades, snow
levels will jump to 5000 to 8000 feet which will keep most west side
activity as rainfall. Substantial rainfall is forecast along the
Oregon coast, with Gold Beach closer to 3 inches and Brookings
closer to 6 inches. Areas south of Cape Blanco are forecast to get 3
to 6 inches of rain. Western Siskiyou County will see similar
amounts of rainfall, while peaks above snow level are forecast to
get 8 to 16 inches of snow. Areas north of Cape Blanco will get 2 to
3 inches of rain, and inland valleys are expected to get 0.5 to 1.5
inches of rain.

The rainfall expected over Curry County supports a Flood Advisory
from tonight at 10 PM through Sunday at 1 AM. Additionally, cold
near-surface air and warm air aloft supports a Winter Weather
Advisory in northwestern Douglas County to address the possibility
of freezing rain. This Advisory is in place from tonight at 7 PM
through Saturday at 10 PM. The highest chances for freezing rain are
along the border of Douglas and Lake counties, with lesser chances
reaching as far as Reedsport and Scottsburg. Due to the amount of
impact that freezing rain can have, extra caution is still advised
for those areas on the southern edges of the warning area.

The Cascades will keep those higher snow levels from traveling too
far east, with snow levels over and east of the Cascades staying at
4000 to 5000 feet through the day Saturday. The Cascade peaks and
higher elevations to the east will see extended periods of snowfall
as the low pressure system moves over the area. Snowfall totals
along mountain slopes are forecast in the 8 to 16 in range while
peaks along the Cascades and in Lake and Modoc counties will
generally see 16 to 32 inches of snow through Sunday morning. Mount
Shasta and some of the Warner Mountains peaks may see even higher
snowfall amounts. Lower elevation areas in Klamath, Lake, and Modoc
counties will still generally see 1 to 4 inches of snow.

The low pressure system is also expected to bring elevated wind
speeds, especially across higher elevations and areas east of the
Cascades. The combination of snowfall and gusty winds supports a
continuing Winter Storm Warning for areas above 4500 feet the
Cascades and in Lake and Klamath counties. A Winter Storm Warning
for areas above 3500 feet around Mount Shasta and for areas of
eastern Siskiyou and Modoc counties will begin at 4 PM this evening.
All Winter Storm Warnings are expected to end Saturday at 10 PM .

An additional area of concern for elevated winds is the Shasta
Valley, with sustained southerly winds of 35 mph and gusts of up to
55 mph possible Saturday morning through the evening. A Wind
Advisory is in place for the Shasta Valley from Saturday at 10 AM
through 7 PM to cover the period where these elevated winds are
possible.

The low pressure looks to weaken and exit the area by Sunday
morning. While some showers may briefly continue, an upper level
ridge will quickly build over the area through the day Sunday and
result in calmer daytime conditions. A drop in Sunday's nighttime
temperatures will bring near or below freezing temperatures to
inland areas west of the Cascades and lows in the teens to low 20s
east of the Cascades. -TAD

.LONG TERM...Monday into Friday

The extended period appears to quiet down significantly compared to
the weather we've seen for much of this week and previous weekend.
We'll see a strong surface high in north eastern Oregon with light
east winds developing across the forecast area Monday afternoon.
Arctic air will attempt to push in from the north late Monday night.
Temperatures do indeed trend lower, but don't hit those extremes
many other locations in north eastern part of the state will see. In
general, lows will hit the lower teens and perhaps the single digits
if skies clear out a bit more or the snowpack really pushes the
temperatures a bit lower.

Ensembles show the next wave pushing towards the region late on
Tuesday with the probability of precipitation increasing mid day
Tuesday.  This upper level wave and weak surface low has a south to
north trajectory, so snow levels will trend higher and the NBM
agrees with this. Snow levels should increase from 4000 feet up to
7000 feet later on Tuesday afternoon and evening. All the members of
the GEFS show pretty weak low centers developing well to our west in
the Pacific around Tuesday, so anything that does happen Tuesday
should produce minimum impacts with regards to winds and
precipitation.

The PoP forecast remains high into Wednesday as this wave continues
to progress through the region.  Perhaps some ensemble members are a
bit slow to move this wave into the Pacific Northwest as well. It's
also worth noting temperatures trend upwards during this time. Highs
are anticipated in the lower 50's for west side valley locations on
Wednesday.  This warming trend will continue further into the week.

In fact, we have some high temperatures reaching up into the lower
60's along the coast and some of the valleys west of the Cascades.
Model guidance seems to be really south to southwest flow towards
the end of the week which is really warming temperatures up.

-Smith

&&

.AVIATION...13/00Z TAFs...Strong winds have eased a bit east of the
Cascades this evening, but remain gusty with turbulence remaining
a risk tonight.

Currently, widespread ceilings (mostly MVFR, but also IFR) are
affecting most of the area west of the Cascades with higher terrain
obscured. Low pressure offshore will bring persistent light to
moderate rain to the coast limiting visibility at times as well.
Snow is falling over the higher terrain. Ceilings tonight will
likely be a mix of MVFR/IFR with the lower conditions most likely in
heavier precipitation.

By Saturday morning, there is a low-level wind shear risk at North
Bend, with weaker SE surface winds and gusty SSW winds just a short
distance off the ground (1500 ft or so). Most likely timeperiod
is from 15-21Z before winds shift to SSW and move onshore during the
afternoon.

With precipitation spreading east of the Cascades tonight into
Saturday morning, expect snow at Klamath Falls that will likely be
moderate to heavy at times. This would result in snow on the runway,
so we've sent an airport weather warning for that. Guidance is
showing snow levels rising overnight and a warm nose moving into
Klamath Falls during the early morning, which could result in a
mixed bag of snow, sleet and freezing rain. Models do, however, show
the temperature rising to near or just above freezing by around 17z.
-Spilde

&&

.MARINE...Updated 200 PM Friday January 11, 2024...South winds
will increase over the waters tonight ahead of the next low
pressure system developing offshore. Latest guidance continues
to show a narrow band of stronger winds developing within 25 NM from
shore later this evening, which could bring gale force gusts and
steep to very steep seas in those areas into Saturday morning. While
lighter winds and lower seas are probable for most of the night
beyond 25 NM from shore, conditions in those areas will still be
hazardous to small craft. The storm deepens to around or even a bit
below 995mb by Saturday afternoon. This will allow for a wind shift
to southwesterly across all the waters Saturday afternoon and
they'll remain gusty (perhaps to still to gale force). For these
reasons, we've gone ahead and upgraded the Gale Watch to a Gale
Warning through Saturday evening. The low is expected to fill and
weaken as it moves onshore Saturday night with winds becoming north
and diminishing to 10 to 20 kt. Even so, steep to very steep short-
period (7 to 11 seconds) seas will persist into the early
hours of Sunday. Finally, the pattern calms down with improved
conditions expected for the first half of next week. -Spilde

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 7 PM this evening to 10 PM PST
     Saturday for ORZ021-023.

     Flood Watch from 10 PM PST this evening through late Saturday
     night for ORZ021-022-024.

     Winter Storm Warning until 10 PM PST this evening above 3000
     feet for ORZ025.

     Winter Storm Warning until 10 PM PST Saturday for ORZ027-028.

     Winter Storm Warning until 10 PM PST Saturday above 4500 feet
     for ORZ029>031.

CA...Winter Storm Warning until 10 PM PST Saturday above 4500 feet
     for CAZ080.

     Wind Advisory from 10 AM to 7 PM PST Saturday for CAZ081.

     Winter Storm Warning until 10 PM PST Saturday above 3500 feet
     for CAZ082.

     Winter Storm Warning until 10 PM PST Saturday for CAZ083>085.

PACIFIC COASTAL WATERS...Winter Weather Advisory from 7 PM this
     evening to 10 PM PST Saturday for PZZ350.

     Gale Warning from 7 PM this evening to 7 PM PST Saturday for
     PZZ350-356-370-376.

     Small Craft Advisory until 7 PM PST this evening for PZZ350-370.

&&

TAD/CZS/MAS