Winter Storm and Heavy Snow in Oregon, December 24 to 27, 2021

Area Forecast Discussion
National Weather Service Medford OR
1034 PM PST Thu Dec 23 2021

.UPDATE...The aviation discussion has been updated.

&&

.AVIATION...24/06Z TAFs...The back edge of a frontal band with light
to locally moderate snow will continue across Lake and Modoc
counties overnight with MVFR conditions. Elsewhere, conditions are
mainly dry with a mix of VFR and MVFR and areas of mountain
obscuration. A brief period of valley IFR is possible in the early
morning hours. In those locales, the next front should bring a
lifting of the stratus deck to MVFR during the morning. Otherwise,
The next front will bring deteriorating conditions to southwest
Oregon, northern Klamath County, and western and central portions of
Siskiyou County early Friday morning through the afternoon with
rain/snow, mountain obscuration, and mainly MVFR with a freezing
level around 3000 feet MSL.

During the afternoon into the evening, the front will continue
across the east side with deteriorating conditions becoming mainly
MVFR with snow while west side precipitation becomes more showery
with the freezing level falling to around 2500 feet MSL. -DW

&&

.MARINE...Updated 830 PM PST Thursday, 23 December, 2021...A
Small Craft Advisory remains in effect overnight. The forecast has
been updated to extend the Hazardous Seas Warning from Friday
through Friday night. Also, the following Small Craft Advisory has
been extended to cover late Friday night through the weekend.

A cold front will move across the waters late tonight into Friday
with increasing westerly winds and steep seas becoming very steep.
Winds will approach gale force around noon with west-northwest seas
building to a peak of around 15 to 19 ft at 12 to 13 seconds Friday
evening. Steep seas then accompany a series of unusually cold
disturbances during the weekend. The pattern is expected to remain
active early next week. -DW

&&

.PREV DISCUSSION... /Issued 836 PM PST Thu Dec 23 2021/

24/00Z NAM in. 24/00Z GFS in through 84hr.

Most west side stations and some east side stations are
reporting light precipitation this evening. The 24/00Z KMFR
sounding indicates that snow levels were near 3500 feet, at
least on the west side, but that is likely dropping rapidly
now. Over on the east side, KLMT has been reporting rain,
Lakeview has reported mixed precipitation, and no
precipitation has occurred recently in Alturas.

The coming week will be quite an interesting one over the Medford
forecast area. High impact snow events look likely at this time,
with snow levels dropping to most of the west side valley floors
by the end of this weekend and staying cold through at least the
middle of next week.

A long wave upper trough is now moving through the Pacific
Northwest along with a surface front. This will bring colder air
into the area and snow levels will drop to around 2000 feet
later tonight into Friday.

The lowering snow levels combined with ongoing precipitation will
make for snow impacts across the area. Winter Storm Warnings and
Winter Weather Advisories are in effect for this time frame. See
PDXWSWMFR for details.

A strong short wave diving down the backside of the trough
will move onshore Friday evening, pushing yet another front
onshore ahead of it Friday morning. This will bring another shot
of cold air to the area. Snow levels will drop to the 1500 to
2000 foot range, which means the higher west side valleys will
see snow. The cold air aloft will support convection, which brings
the possibility of thunderstorms to at least the west side Friday
morning into Saturday morning. Snow levels may lower locally with
the higher precipitation rates as well.

The upper level trough will remain overhead into next week with
short waves moving through. This will support additional rounds of
convection with cold air in place. Snow levels will continue to
drop, down to 1000 to 2000 feet Saturday, mostly below 1000 feet
Saturday night, then back up to 1000 to 1500 feet Sunday.
Convection will likely be strong enough to locally lower snow
levels even to the lowest west side valley floors.

Travelers should be prepared for significant impacts including
snow across all area passes Friday then down to some lower valley
floors this weekend into Monday. Travel could be very difficult to
impossible at times and road closures are possible. Anyone
traveling Friday through Monday should check conditions road
before leaving, carry a winter emergency kit, and if possible,
consider alternate travel plans during periods of heavy snow.

Extended discussion from the Thursday afternoon AFD...Sunday 26
Dec through Thursday 30 Dec 2021.

Sunday is a major holiday weekend travel day with the possibility
of major winter weather impacts.

Colder air will be in place Sunday with a moist onshore flow and
disturbances that will bring snow to lower valleys down to mainly
1500 to 2000 feet. Significant winter weather could impact the
region including the Interstate 5 passes between Grants Pass and
Roseburg as well as Siskiyou Summit near the California-Oregon
border. There is still some uncertainty regarding how far the
northern edge of the heavier precipitation will reach. It looks like
the Mt. Shasta Region will almost certainly be hit with heavy snow
Sunday into Monday morning but there is more uncertainty with how
far north and for how long a duration the low elevation snow will
occur across southern Oregon. The chances of it occurring are high
enough to warrent a Winter Storm Watch from midday Saturday to
midday Monday.

An upper trough will push the heavier precipitation south and east
of northern California by Monday morning or afternoon. Away from the
shoreline, snow showers will occur behind the trough but not steady
and heavy snow. A more northerly flow will also bring even colder
air into the region Tuesday and Wednesday. Low elevation snow
showers are possible down to the lowest westside valley floors
Tuesday through Thursday but it will be a generally drier pattern.
Any fresh snow on the ground combined with light to calm winds and
clear or partly cloudy skies could allow low temperatures to reach
the teens in the westside valleys, and down to single digits below
zero across colder parts east of the Cascades.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 4 AM PST Friday for ORZ029>031.
     Winter Weather Advisory from 10 AM Friday to 10 AM PST Saturday
     for ORZ029>031.
     Winter Storm Watch from Saturday morning through Monday morning
     for ORZ029-030.
     Winter Storm Warning from 4 AM Friday to noon PST Monday above
     1500 feet in the for ORZ023-024.
     Winter Weather Advisory from 6 AM Friday to 10 AM PST Saturday
     above 1500 feet in the for ORZ025-026.
     Winter Storm Watch from Saturday morning through Monday morning
     for ORZ025>028.
     Winter Weather Advisory until 4 AM PST Friday for ORZ027-028.
     Winter Storm Warning from 6 AM Friday to 10 AM PST Saturday
     above 2000 feet in the for ORZ025-026.
     Winter Weather Advisory from 6 AM Friday to 10 AM PST Saturday
     for ORZ028.
     Winter Storm Warning from 6 AM Friday to 10 AM PST Saturday for
     ORZ027-028.

CA...Winter Weather Advisory until 4 AM PST Friday for CAZ085.
     Winter Weather Advisory from 6 AM Friday to 10 AM PST Saturday
     above 1500 feet in the for CAZ080.
     Winter Storm Watch from Saturday morning through Monday morning
     for CAZ080-082-083.
     Winter Storm Warning from 6 AM Friday to 10 AM PST Saturday
     above 2000 feet in the for CAZ080.
     Winter Weather Advisory until 4 AM PST Friday above 4000 feet in
     the for CAZ080-082-083.
     Winter Storm Warning from 1 PM Friday to 10 AM PST Saturday for
     CAZ082-083.
     Winter Weather Advisory from 1 PM Friday to 10 AM PST Saturday
     for CAZ081.
     Winter Weather Advisory from 1 PM Friday to 10 AM PST Saturday
     for CAZ084-085.

Pacific Coastal Waters...
     Small Craft Advisory until 4 AM PST Monday for PZZ356-376.
     Small Craft Advisory until 4 AM PST Friday for PZZ350-370.
     Small Craft Advisory from 1 AM Saturday to 4 AM PST Monday for
     PZZ350-370.
     Hazardous Seas Warning from 4 AM Friday to 1 AM PST Saturday for
     PZZ350-370-376.

15/15/16

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MEDFORD OR
649 PM PST THU DEC 23 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0649 PM     HEAVY RAIN       4 N GRANTS PASS         42.50N 123.34W
12/23/2021  M1.50 INCH       JOSEPHINE          OR   TRAINED SPOTTER

            12 HOUR TOTAL 0630-1830 PST.

&&

JRS