Winter Storm in California, March 15 to 18, 2025

Area Forecast Discussion
National Weather Service Medford OR
910 AM PDT Sat Mar 15 2025

.SYNOPSIS...

An impactful winter storm and atmospheric river will hit southern
Oregon and northern California on Sunday with feet of snow in the
central Cascades and inches of rain west of the Cascades. Model data
suggests this will be an unusually wet and snowy storm this time
of year for the region. This system will result in major travel
impacts in the high Cascades due to snow accumulation with minor
to moderate flooding impacts looking likely west of the Cascades
during Sunday and Monday.

.DISCUSSION...

Latest satellite and radar data suggests we might see some weak
thunderstorms pop up along the coast this morning. KMAX is picking
up some 50dbz echos just south of Port Orford with GOES 18
detecting some cloud flashes farther up the Oregon coast. Sounding
data hints the clouds will be cold enough for charge generation
later this morning. In any case, the chance for some weak
thunderstorms and heavy showers will persist into the late morning
hours.

Read the previous discussion below for more information on the
upcoming weather hazards.

&&

.AVIATION (12Z TAFs)...

A combination of strong wind speeds, showers, and ceilings will lead
to MVFR--in some cases IFR--through this TAF cycle as a front passes
through the region today/tonight. There will also be a strong low
level jet leading to wind shear at the terminals. This jet could be
as low as 1000 feet with speeds between 50 and 60 knots likely.
Overall, unfavorable conditions are likely through the entire TAF
cycle.

-Guerrero

&&

.MARINE...Updated 830 AM Saturday, March 15, 2025...Seas will
remain very steep and hazardous through this afternoon. A strong
front will approach the waters this afternoon bringing strong south
winds reaching gale force by late this afternoon/early evening. Wind
speeds will significantly diminish by Sunday morning, and Gales will
be confined to the southern waters mainly south of Port Orford.

The front will move south of the waters later Sunday afternoon and
any south component to the winds Sunday afternoon will be weaker.
However, very steep and hazardous Seas are likely to persist through
Sunday afternoon, followed by Small Craft conditions Sunday night
through Monday. Winds and seas are expected to gradually diminish
Monday with calmer conditions possible Tuesday before south winds
increase again my mid week as another front approaches.

-Schaaf/Guerrero

&&

.PREV DISCUSSION... /Issued 508 AM PDT Sat Mar 15 2025/

DISCUSSION...Shower activity continues this morning, though
coverage has decreased quite a bit since last night. Snow levels
will hover around 3000 ft, but with the hit and miss nature of
showers, any winter impacts will be limited except outside of the
Cascades where shower activity will be more persistent. Though
we're in a relative lull in the active weather, a Winter Storm
Warning remains in effect for the Cascades to encompass recent and
upcoming winter weather. This relative break in the weather will
continue through the morning, and snow levels will gradually rise
to around 5000 ft by late this afternoon. Conditions will
deteriorate across the region later today as the next, most
impactful system in the series moves into the area today.

Overall, the forecast remains on track and much of the discussion
from the Friday (3/14) day shift remains valid:

Active weather will continue area wide this weekend culminating with
a very strong atmospheric river (AR) with high IVT which will take
aim directly at SW Oregon and NorCal late Saturday through Sunday.
This will bring lots of rain, snow and wind, which are detailed
below.

RAIN/FLOODING:  In terms of QPF/model climate, recent model guidance
(the ECMWF Extreme Forecast Index or EFI) is showing high confidence
in an extreme precipitation event in our area for this period (mid-
March). Widespread amounts of 3 to 6 inches are likely from the
Cascades west with slightly less (1 to 3 inches) in the west side
valleys, but even more than that in the coast ranges (6 to 8
inches). The predicted amounts don't quite lie outside the model
climatology. That is to say, they have happened before at this time
of year. But, they do lie at the top end of the climatology. The
copious amounts of precipitation will, at a minimum, lead to high
flows on area streams, creeks, rivers. As such, there is also a high
high risk of areal flooding, ponding of water on roadways as well as
urban, small stream and even main stem river flooding as river
systems get stretched to deal with all the runoff. Snow melt could
also add to the runoff as snow levels rise to 5000-6000 feet later
today into early Sunday. This also increases the risk of rock and
land slides. Given all of that, Flood Watches are in place for all
areas west of the Cascades for late this afternoon through Sunday
evening. River flood watches are also in effect, including the Rogue
River at Agness, the Coquille River at Coquille, the South Fork of
the Coquille at Myrtle Point, and Deer Creek at Roseburg. Other
rivers may need to be added with time, so residents and those with
interests near rivers/streams/creeks should monitor rising water
levels and be prepared for possible flood warnings. Details on the
current watches can be found at FFAMFR. -Spilde

SNOW: In addition to all the rain, there will be snow, and a lot of
it over the Cascades/Siskiyous. Strong winds will also accompany the
snow, especially tonight/Sunday. The Winter Storm Warning in those
areas goes through late Sunday evening. Snow will be measured in
feet up there and there could be a period of time during the peak of
precipitation late tonight into Sunday where snowfall rates could be
in the 1-2"/hour range. With the wind, this would result in very
limited visibility and local whiteout conditions. Latest forecasts
have increased snow amounts some, and now amounts over 4 feet are
possible up around Crater Lake. Winter Storm Warnings remain in
effect this afternoon through Sunday evening above 4500 feet in the
mountains of NorCal, as well as over portions of the East Side. Snow
levels do rise Saturday and while some snow may initially stick
along I-5 at the higher passes (Siskiyou Summit/Black Butte Summit),
the main winter impacts with this one will be above the passes (but
will likely affect Snowman Summit on Highway 89 east of Mt Shasta
City). Areas north of Chiloquin in the northern part of Klamath and
parts of Lake County will be in the transition zone where heavy
precipitation will also meet rising snow levels. If it remains all
snow up there, Highway 97 could receive quite a bit. We do think
most areas along Highway 140 get into the warm sector with a change
to rain Sunday, but this is less certain farther north and the
reason for the warning. -Spilde

WIND: Another aspect of this storm will be strong damaging winds. A
surface low along the front will deepen some as it moves inside of
130W, moving inland just south of the OR/WA border. This will bring
widespread strong winds to the region, especially along the Coast,
in the Shasta Valley, East of the Cascades and across the higher
terrain. Winds will start increasing this afternoon, but really ramp
up this evening and overnight as pressure gradients peak. The North
Bend-Arcata gradient is forecast to peak at -10 mb as is the Medford-
Redding gradient. These values are are common indicators of damaging
winds along the Coast and in the Shasta Valley. Typically, we'd be
concerned with strong winds in the Rogue Valley as well with this
strong of a gradient, but in this case, the winds are lacking the
southeast component that is needed to align with the Rogue Valley
and allow for strong winds to funnel in there. That said, however,
these winds will be will have a strong southwest component, and that
is likely to equate to stronger winds for the Illinois Valley and
other southwest oriented locations west of the Cascades. As such,
have included portions of Jackson/Josephine/Douglas counties in a
Wind Advisory for this system.

Strong winds are also expected east of the Cascades as 700 mb flow
peaks around 60 to 75 kts. For locations where a Winter Storm
Warning is in place, these strong winds are wrapped into that
product. Some adjustments were made to broaden the High Wind Warning
across all of Modoc County and into far northeastern Siskiyou
County. Additionally, a Wind Advisory was added to the remainder of
the Klamath Basin (including Klamath Falls) eastward to Lakeview.

The front will gradually sag southward Sunday morning, bringing an
end to the stronger winds along the coast and west of the Cascades.
Adjustments were made to the end time of some wind headlines
accordingly. However, a secondary, weaker, surface low looks to
develop along the front Sunday morning and this will maintain
stronger winds across the East Side into the afternoon/evening
hours. It's not out of the question for winds to briefly touch
warning criteria in the Klamath Basin where the Wind Advisory is in
place as this secondary low pushes through.

Winds will diminish for all areas overnight Sunday and that will be
the end of the wind threat through at least mid-week. For details on
the varying wind headlines, please see NPWMFR. /BR-y

The main front/AR will get a push inland late in the day Sunday.
Colder air will filter in behind the front Sunday afternoon, and
snow levels will lower down to around 3000 ft Sunday night into
Monday. Before this happens, however, there are some indications
that snow levels could lower to around 2500 ft for a period of time
at the back end of the front for areas north of the Rogue-Umpqua
Divide. High resolution guidance is showing the potential for a
brief period (3-6 hours) of moderate snow at the passes north of
Grants Pass early Sunday afternoon. Much will depend on the timing
of when snow levels lower and when the heavy precipitation wanes,
but this is something worth monitoring and will let the day shift
determine if any winter headlines are warranted.

Otherwise, precipitation becomes showery again behind the front as
it moves south and east of the Cascades late Sunday. Models are
still showing the upper trough swinging through on Monday, so while
showers will be more hit-or-miss, there is still a high probability
of precipitation. The good news is that guidance is showing a break
in the action Monday night through at least Wednesday morning.
Tuesday will probably be a transition day with showers tapering off
into dry conditions under a short wave ridge passing through the
area. This break in the weather will be short lived with another
front quickly moving in late Wednesday (more typical for this time
of year) and active weather looks to continue through the latter
half of the week and into the following weekend. /BR-y

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning until 11 PM PDT Sunday for ORZ027>031.

     Flood Watch from 5 PM PDT this afternoon through Sunday evening
     for ORZ021>026.

     High Wind Warning from 5 PM this afternoon to 5 PM PDT Sunday
     for ORZ021-022-031.

     Wind Advisory from 5 PM this afternoon to 8 AM PDT Sunday for
     ORZ023-024-026-029-030.

CA...Winter Storm Warning until 11 PM PDT Sunday for CAZ080-082-083.

     Flood Watch from 5 PM PDT this afternoon through Sunday evening
     for CAZ080.

     High Wind Warning from 5 PM this afternoon to 5 PM PDT Sunday
     for CAZ081-084-085.

PACIFIC COASTAL WATERS...Hazardous Seas Warning until 5 PM PDT this
     afternoon for PZZ350-356-370-376.

     Gale Warning from 5 PM this afternoon to 11 AM PDT Sunday for
     PZZ350-356-370-376.

&&