Winter Storm in Oregon, February 25 to 27, 2024

Area Forecast Discussion
National Weather Service Medford OR
913 PM PST Sun Feb 25 2024

.SHORT TERM...Models remain on track with a front down from the
north this evening. This front will move across the area late
tonight through Monday afternoon. Light precipitation has spread
into areas of Coos and northwest Douglas counties this evening.
High resolution models show the main band of precipitation with
the front moving down across southwest Oregon late tonight and
Monday morning, then across northern California zones Monday
morning into Monday afternoon. This frontal system will bring
rain, heavy mountain snow and strong gusty winds over the
mountains and east side. Behind the front, an upper trough moves
into the area and expect scattered to numerous showers, with
shower activity lingering Monday night and Tuesday (especially for
areas from the Southern Oregon Cascades west).

Snow levels will lower from 5000 to 6000 feet this evening down
to around 3000 to 4500 feet with the frontal passage, then down to
around 1700-2500 feet behind the front as showers spread into the
area on Monday. These lower snow levels will initially affect
areas from the Southern Oregon Cascades west and across Klamath
and northern Lake County by late Monday morning, then will affect
all areas by early Monday evening. With moist, onshore westerly
flow, heavy snow is forecast in and near the southern Oregon
Cascades tonight through Monday, with heaviest snowfall rates
late tonight and Monday morning. Additionally, gusty winds will
develop across the higher mountains and east of the Cascades as a
strong mid level jet moves into the area (50-60 kt at 700 mb).
Very low visibilities are expected for areas that see moderate to
heavy snow and gusty winds, especially across exposed terrain in
the Southern Oregon Cascades and in northern Klamath County east
of the Cascades. A winter storm warning remain in effect for these
areas. Additionally winter weather advisories are in effect for
higher mountains east of the Cascades in Siskiyou, Modoc and
northern Lake counties. Lower mountain passes may see localized
snow impacts during the day Monday, mainly in Douglas County where
snow levels will lower down to 1700-2000 feet Monday morning into
Monday afternoon. This may bring a rain/snow mix or periods of
light snow in showers to Canyon Mountain Pass on I-5. However,
warmer ground temperatures are expected to result in melting snow
and limited impacts.

The front will exit to south late Monday afternoon. However, a
cold and showery air mass which moves into place immediately
behind the front will remain over the area Monday evening and
night. Showers are expected across the area Monday evening,
decreasing in coverage and intensity MOnday night. Precipitation
will be mainly light in showers Monday evening/night (but
moderate along and near the Cascades). Models continue to show
snow levels lowering further, down to 1000 to 1500 feet Monday
night. However, with mainly light precipitation in showers expect
limited impacts. The best chance of showers Monday night will be
from the Southern Oregon Cascades and westward across Douglas,
Coos, and Curry county with isolated to scattered showers in
Josephine, Jackson, northern Klamath and northern Siskiyou
counties. Then, models continue to indicate light precipitation
lingering across areas from the Cascades west on Tuesday.

&&

.AVIATION...26/00Z TAFs...LIFR ceilings have covered sections of the
coast this evening ahead of the next cold front.  Look for LIFR to
MVFR ceilings through the night as moderate rain moves in.  Low
level wind shear will also be a concern east of the Cascades this
morning as winds around 2000 to 2500 feet are around 35 to 40 knots
with lighter winds in the valley.  Those concerns will diminish by
the later morning hours.

MVFR ceilings will remain more likely through Monday as the
atmosphere begins to destabilize under the heavier rain showers.
There is a low chance of lightning around the Umpqua Basin and the
central Oregon coastline near North Bend(KOTH) and Roseburg(KRBG).
Pockets and longer periods of VFR ceilings will also develop between
the showers later in the afternoon and evening hours.

-Smith

&&

.MARINE...Updated 830 PM Sunday February 25, 2024... A strong cold
front will bring gusty northwest winds and steep seas into Monday.
The current forecast continues to show steep seas across all waters,
with peak wind gusts of 25-30 knots and waves of 10 to 13 feet at 12
to 14 seconds. Because of these conditions, a Small Craft
Advisory is in effect.

Winds will ease Monday night into Tuesday, but persistent west swell
is expected to sustain steep seas (hazardous to small craft) for all
waters. Another strong front will bring increasing south to
southwest winds Tuesday night that will continue Wednesday into
Thursday with steep to very steep seas. These conditions are likely
to be present in all waters to end the week with the latest guidance
suggesting a potentially very high and very steep swell (15-19 feet
at 15 seconds) arriving Thursday and lasting into the weekend. The
peak wave heights are forecast on Friday, March 1st.

-Smith/Hermansen

&&

.PREV DISCUSSION... /Issued 317 PM PST Sun Feb 25 2024/

SHORT TERM...Tonight through Tuesday night (2/27)...A strong cold
front moving southeast is just reaching the vicinity of Astoria on
the far northern Oregon coast. The front will continue across
Oregon tonight through Monday morning, and exit our portion of northern
California during Monday afternoon. A period of generally lighter rain
and snow showers in the coldest air mass we have had since January
will follow Monday night.

The associated winter weather headlines that begin late this
evening were updated to expand the Winter Storm Warning to include
the foothills of Jackson County, above 2500 feet early Monday
morning into Monday evening. Westerly upslope winds will focus
snowfall on the southern Oregon Cascades, and into northern
Klamath County with 8 to 22 inches expected late this evening
through Monday night. Snowfall intensity will be highest during
Monday morning. A lesser but noteworthy impact of around 4 to 10
inches of snow will be on other west facing slopes, including the
northern California portion of the Cascades, and the Warner
Mountains. Gusty southwest to west winds through Monday evening will
be strongest over the higher terrain and east of the Cascades
late tonight through Monday morning, with the frontal passage.

Snow levels will be near 5500 feet at precipitation begins, are
forecast to fall to 4000 to 5000 feet by 4 AM PST Monday, then
2000 to 3000 feet by 10 AM, around 2000 feet in the afternoon,
then 1000 to 1500 feet as precipitation tapers off Monday evening.
Our recent and still ongoing episode of much warmer than normal
temperatures will delay the onset of snow accumulation and at
least somewhat hinder snowfall totals. While this system will be
most noteworthy for low snow levels and Cascade snowfall totals,
most valleys will receive an inch or less of snow.

A weaker frontal system, focused north of our area, will brush
past on Tuesday into Tuesday night with light showers mainly for
the coast and Douglas County northward, with snow levels rising
back to around 2500 feet.

LONG TERM...Wednesday(2/28) through Sunday(3/3)...Showers will
continue along the coast and into the Umpqua Basin Wednesday as a
weak warm front passes through the area. Precipitation amounts will
be light, and with snow levels rising to 4000 to 5000 feet, no
winter impacts are expected.

The big story then begins late Wednesday. A very broad and strong
upper level trough over the Gulf of Alaska will dig southeast and
intensify, approaching the coast of the Pacific Northwest by
Wednesday night, then slowly but surely moving into and passing
through the region Thursday through Saturday. The general pattern
during this time, including the strength, track, and timing of this
trough, remain in near universal agreement across the model suites,
so confidence remains high that we will have an impactful multi-day
event, mostly divided into two phases: the frontal passage, and the
post-frontal showers, the latter of which could easily result in
snow over the valley floors of the West Side.

First the frontal passage itself. Winds will begin increasing at the
coast Wednesday afternoon, with gusty southwest winds then spreading
to the rest of the area Wednesday night into Thursday morning, with
the cold front itself finally passing through the forecast area
Thursday afternoon. Forecasted pressure gradients and model mid-
level wind fields ahead of the front (70-80 kt at 700 mb!) suggest
that winds are more than likely going to reach High Wind thresholds,
particularly along the coast, over the ridgelines, across the East
Side, and in the Shasta Valley, and perhaps even the southern Rogue
Valley near Ashland as well, although the direction of the mid-level
winds does not appear to fully align with the valley orientation, so
winds may not be as strong there.

Meanwhile, moisture transport values have increased in the latest
runs, and wile not exceedingly strong, are strong enough to suggest
a good shot of precipitation from Wednesday night until the front
passes Thursday afternoon (with the likely exception of the Medford
area, where systems such as these typically underperform due to
downsloping effects off the Siskiyous). Rainfall amounts will be
healthy, but not excessive, and with snow levels of 4000 feet or
higher ahead of the front, winter impacts will be relegated to the
Cascade passes and the higher terrain of the Klamaths. Here, several
inches of snow are forecast to fall Thursday, and winter headlines
are likely to be in place throughout the day.

Behind the front, a much colder air mass will arrive. Temperatures
Friday into the rest of the weekend will be more typical of early
January than early March. Snow levels will lower quickly behind the
departing front, reaching 1000 to 2000 feet by Thursday night, and
will fall even lower Friday into Saturday. The bulk of precipitation
will have fallen by the time snow levels bottom out, but with the
trough still approaching and passing overhead through the weekend,
showers will be an ongoing feature for the remainder of the extended
term. Snow could easily reach valley floors during this time, and
snowflakes may even make an appearance at the coast. Showers will be
ongoing, so snowfall will be sporadic, although heavily focused on
higher terrain and the western slopes, where several more inches of
snow are possible. Snow amounts in the valleys should be light, and
with warm ground temperatures may not stick around very long. All
told, snow amounts over the Cascades, Klamaths, and the high terrain
of the East Side could easily reach 2 to 3 feet from Thursday
through Sunday.

The trough finally exits to the east Sunday, with showers tapering
off through the afternoon and snow amounts trending more towards
nuisance amounts. With skies clearing and plenty of fresh snowpack
in the area, temperatures Sunday night could be very cold, with
single digits or even sub zero lows east of the Cascades, and a
chance for frost or freeze along the coast. -BPN

BEACH HAZARDS...Updated 230 PM Sunday February 25, 2024...Long
period westerly swell is present and the beach hazards statement for
sneaker waves looks on track. These long period waves are running in
the 6-8 ft range interspersed with another wave set of similar
direction/height, but with a period of 12 seconds. Some of the
longer period, higher energy waves will have the ability to run much
farther up the beach than usual. The sneaker wave threat will
continue tonight, but will diminish by Monday morning with wave
periods lowering below 15 seconds. Looking ahead to the end of this
week, current model guidance is showing a very high swell moving
into the waters Thursday into Friday. This could result in high surf
conditions with breakers in the surf zone of 23-26 feet.
-Spilde/Hermansen

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 4 AM Monday to 1 AM PST Tuesday for
     ORZ031.

     Wind Advisory from 1 AM to 10 PM PST Monday for ORZ031.

     Beach Hazards Statement until 4 AM PST Monday for ORZ021-022.

     Winter Storm Warning until 1 AM PST Tuesday for ORZ025-027-028.

     Winter Storm Warning from 4 AM Monday to 1 AM PST Tuesday above
     2500 feet for ORZ026.

     Winter Storm Warning until 1 AM PST Tuesday for ORZ030.

CA...Winter Weather Advisory from 4 AM Monday to 1 AM PST Tuesday for
     CAZ082>085.

     Wind Advisory from 1 AM to 10 PM PST Monday for CAZ084-085.

PACIFIC COASTAL WATERS...Small Craft Advisory from 7 AM Monday to 4
     PM PST Tuesday for PZZ356-376.

     Small Craft Advisory from 1 AM Monday to 4 PM PST Tuesday for
     PZZ350-370.

&&

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