Flood in Oregon, January 1, 2025

Area Forecast Discussion
National Weather Service Medford OR
919 PM PST Tue Dec 31 2024

...Updated the aviation and marine sections...

.AVIATION...01/06Z TAFS...Ceilings continue to lower west of the
Cascades this evening as the next front moves across this evening
with widespread rain and snow. The front will continue across the
east side overnight with areas of light to briefly moderate snow.
Snow levels around 3500 ft MSL will rise to 5000 feet MSL Wednesday
morning, then 6000 feet by Wednesday evening. Overall, expect mixed
MVFR/VFR ceilings with higher terrain obscuration overnight then a
mix of MVFR and IFR Wednesday into Wednesday evening, with areas of
LIFR developing toward sunrise and continuing through the morning,
including at Roseburg and Medford.

Snow will reduce conditions to LIFR at Klamath Falls late tonight
into Wednesday morning and could result in an inch or more of
accumulation on the runway. An airport weather warning is in effect
from 10 pm PST this evening through 7 am PST Wednesday. The front
will stall and lift back north as a warm front later Wednesday, so
that will keep light precipitation and the lower conditions around
into Wednesday evening. -Spilde/DW

&&

.MARINE...Updated 830 PM PST Tuesday, December 31, 2024...A narrow
cold front will continue steep seas tonight, with gusty south winds
over the inner waters through the night. This will cause hazardous
conditions to small craft with winds in the 20-30 kt range. Brief
gale force gusts around 35 kt are possible, along with brief periods
of very steep seas (10 ft at 7 secs). The strong winds will linger
longest, into Wednesday morning, in the inner waters south of Cape
Blanco

Overnight into Wednesday morning, winds will ease behind the front.
However, another front and elevated west swell will maintain steep
combined seas of 9-12 feet into Thursday. A stronger front Thursday
night into Friday night could bring gales and steep to very steep
seas followed by large steep swell (~15-18 ft) later Friday into
Saturday morning. Uncertainty remains, so we'll keep monitoring the
latest data and adjust forecasts accordingly. Another weaker storm
could move through during the second half of the weekend, but latest
guidance suggests a period of high pressure and north winds
developing early next week. -Spilde/DW

&&

.PREV DISCUSSION... /Issued 358 PM PST Tue Dec 31 2024/

DISCUSSION...Dry conditions continue for most areas early this
afternoon, but there is plenty of cloud cover in advance of the next
system. A front will push onshore over the next few hours, spreading
precipitation inland through this evening and overnight with a
secondary stronger front moving quickly in Wednesday morning. Snow
levels will initially be around 2500-3000 ft with this initial push,
but will quickly rise to around 5000 ft by Wednesday afternoon. We
expect some wintry impacts to the Cascades as well as some East Side
locations like the Highway 97 corridor from Chiloquin northward.
Current forecast brings about 8-12 inches for the Cascades with 2-4
inches for the Highway 97 corridor. A Winter Weather Advisory
remains in place for this, and details can be found at WSWMFR. With
snow levels down that low at the onset, there could be some light
snow in the Mt Shasta City region, but since this a westerly flow
system and not southerly, impacts will be focused on the Cascades
and limited to the higher elevations of western Siskiyou in northern
California.

The secondary front will move in on swift (35-45 kt) mid-level
westerly flow and this will bring some enhanced breezes to the
region on Wednesday. Right now it looks like winds should remain
below advisory criteria, but gusts of 25-35 mph will be common along
the coast, east of the Cascades and across the higher terrain.
Models do indicate a brief 55 kt maximum that moves through
Wednesday afternoon, which could result in a brief period of
advisory level winds east of the Cascades, but for now we'll monitor
model trends. Swift mid-level westerly flow will continue into
Thursday, and this will maintain gusty winds and precipitation along
the coast and Cascades. Snow levels will be up around 6000-7000 ft
during this time, so overall, impacts will be minimal through
Thursday night.

At this time, it looks like the most potentially impactful system of
the week will be the Friday into Saturday system because it will
also be the wettest system of the week. Models bring a deepening
surface low along 130 W, and bring the surface low inland somewhere
between Cape Blanco and Vancouver Island. As to be expected, there
are varying differences in strength and location/trajectory of this
surface low, but this could bring some stronger winds to the region.
Current guidance indicates high end advisory level winds across the
East Side and possibly in the Shasta Valley, but this could change
if the models trend farther east with the deepening low. We'll
monitor model trends and make adjustments as necessary. A cold front
will swing through the region late Thursday night through the day
Friday. Snow levels will be high initially (6000-7000 ft), then
lower to around 5000 ft with the front and down to around 4000 ft
behind the front Friday night into Saturday. This will bring another
round of snow to the Cascades that will likely result in some winter
headlines. Precipitation turns more showery late Friday into
Saturday when those snow levels are down to around 4000 ft, so
winter impacts will be limited under the showery regime.

A few more weaker systems will follow Sunday into Monday with snow
levels hovering around 4000-5000 ft. Precipitation amounts look to
be fairly light during this time so we aren't anticipating much in
the way of impacts after Saturday. Beyond the weekend, there is
pretty good agreement among the models/ensembles on an extended dry
period starting on or around January 8th. /BR-y

HYDROLOGY...Rivers continue to recede around the region, with
the exception being the Coquille at Coquille as usual. It remains
in moderate flood stage this afternoon, and is forecast to come
down to minor flood stage by this evening. There's some
uncertainty regarding how soon it comes down below minor flood
stage. Current forecasts indicate this could happen Wednesday
morning, but it's possible that it takes a bit longer and remains
in flood stage until early Thursday.

Considering antecedent conditions with all the recent rain we've had
and ongoing flooding, there may be some concern for another flood
event this week as the rain returns. At this time, it does not look
like that is the case. Total rainfall amounts from late Tuesday
through early Saturday range from 2-4 inches along the coast, 1-2
inches for inland areas west of the Cascades (up to 3 inches in the
wetter locations) and 0.50-1 inch east of the Cascades. Looking at
our mainstem river forecasts, all rivers show some increase after
the Friday system. The Coquille at Coquille looks to reach bankfull
and possibly approach minor flood stage, while the Rogue River at
Agness also gets close to bankfull. The other rivers are forecast to
remain below action stage at this time.

For reference, 3-day rainfall totals from this previous Friday-
Sunday, there was 3-5 inches along the coast, 2-3 inches for inland
areas west of the Cascades and 0.5-2 inches east of the Cascades.
That's not including all the precipitation that fell before and on
Christmas day. The amounts mentioned above is what we have forecast
over a 96 hour time frame and is generally less than what occurred
over the previous 72 hours. The systems expected this week are
expected be more typical for this time of year. After the upcoming
weekend, there is fairly good agreement on a dry period beginning on
or around the 8th of January. /BR-y

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until noon PST Wednesday for ORZ027>030.

CA...Winter Weather Advisory until noon PST Wednesday for CAZ080.

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

&&