Winter Storm in California, February 1 to 4, 2025

Area Forecast Discussion
National Weather Service Medford OR
256 PM PST Sat Feb 1 2025

.DISCUSSION...

Key Points:

* Southern Oregon and northern California will remain in a
  relatively wet and complex pattern for the next several days
  with an atmospheric river and low pressure system dominating our
  weather.

* Snow levels will begin to drop tonight into Monday, and could
  reach as low as 500 feet by Monday morning. This could bring
  snow to valley floors west of the Cascades.

* Periods of moderate to heavy precipitation will be possible in
  the higher elevations of southern Oregon and northern California
  tonight through Sunday night.

A long duration complex pattern has set up across southern Oregon
and northern California and will continue to persist for the next
several days. This has brought wet weather to our area with snow
in the mountains and rain across the lower elevations. Radar
continues to show showers across portions of Oregon and more
steady precipitation in California.

This is set up by a low pressure system dipping southward over the
Gulf of Alaska and several atmospheric rivers that will parade
across the area through next weekend. The low will meander across
the area and should remain mostly offshore, but as this low sinks
southward, snow levels and temperatures will be allowed to
plummet with northerly flow. Meanwhile, this will also affect the
atmospheric rivers moving through the area. Most of the moisture
will target Humboldt and Del Norte County, but ensembles are
showing considerable inland penetration as well to include
Siskiyou, Modoc, and southern Klamath and Lake Counties.
Precipitation will also exist to the north and the south of this
moisture plume, and this is where the forecast becomes
interesting. Have issued a plethora of winter products across
California and East of the Cascades through Sunday night.

The setup reminds me a bit of the February 2019 atmospheric river
that wrecked havoc across Douglas County, however this set up is
expected to be farther south. Still, we could see some low
elevation snowfall beginning tomorrow with snow levels falling to
2000 feet on Sunday before falling again to around 500 feet by
Monday morning. However, am lacking a lot of confidence in the low
elevation snow forecast for Monday since this forecast represents
a new trend of bringing those atmospheric rivers a bit farther
north--meaning an increase in both rain and snowfall across the
area. That and guidance is all over the place. The National Blend
of Models ensemble guidance suggests a 15% chance for snow on the
Rogue Valley Floor and a 20 percent chance for a dusting of snow
in Roseburg. However, the HREF and the SREF, the GEFS and EC
Ensemble all suggest much higher probabilities for snowfall in
the Rogue Valley (and somewhat higher across Douglas County). In
fact, the model spread for snow at the Medford airport is anywhere
between 0 and 6 inches for Monday morning. Have gone with the
deterministic National Blend of Models solution which puts 2
inches of snow in Medford, 1 and a half inches in Grants Pass, 3
Inches in the Illinois Valley and a half an inch in Roseburg.
Would like to see this forecast persist for one more model run
before issuing any low elevation products.

Guidance then suggests that the low continues to dip southward and
that snow, event at valley floors, will continue through at least
mid-week. This is where snow may even be possible at the beaches.
This also means that temperatures are going to be particularly
cold as well. Overnight low temperatures both Tuesday and
Wednesday mornings will reach the low to mid 20s across the West
Side, freezing temperatures at the beaches, and in the teens to
single digits possible in California and along and East of the
Cascades.

Conditions will persist (although may be a little warmer) through
the week, with continued unsettled weather with increased
precipitation chances. Stay tuned to the forecast for more
information on the low elevation snows continuing through the
extended forecast. -Schaaf

&&

.AVIATION...01/18Z TAFs...Mostly MVFR conditions are seen with some
showers except for parts of the Rogue Valley with IFR/LIFR this
morning. The higher terrain will continue to be obscured.

Stable conditions this afternoon through this evening could result
in lowering ceilings with ceilings lowering to IFR with patchy to
areas of fog possible west of the Cascades. Moisture moving up from
the south later tonight could result in reduced visibility and
ceilings due to light snow at Klamath Falls. This moisture could
also move into Medford which could result in increased visibility.
For now the TAF at Medford shows reduced visibility this evening
until the end of the TAF period, but they could come up if
precipitation lifts far enough north. There is around a 40%
probability to see IFR ceilings tomorrow morning in the Rogue Valley
and east of the Cascades, so only forecasting IFR visibility for
now. -Petrucelli/Hermansen

&&

.MARINE...Updated 200 PM Saturday, February 1, 2025...Light to
moderate west to northwest winds will continue today, then become
northerly tonight. Winds will remain below small craft, however
northwest swell is expected to hover around 8 to 10 feet the next
few days.

Low pressure will persist early next week with swell dominated seas
expected to remain below small craft. -Hermansen

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 3 AM PST Sunday for ORZ029>031.

     Winter Storm Warning from 4 AM Sunday to 4 PM PST Monday for
     ORZ029>031.

CA...Winter Weather Advisory until 3 AM PST Sunday for CAZ080>085.

     Winter Storm Warning from 4 AM Sunday to 4 PM PST Monday for
     CAZ080-082>085.

PACIFIC COASTAL WATERS...Small Craft Advisory until 4 PM PST this
     afternoon for PZZ350-356-370-376.

&&