NWS Medford, OR wrote its last area forecast discussion before the first event at Dec 11, 2:49 PM PST, 1 hour earlier.
Area forecast discussion, Dec 11, 2:49 PM PST, 1 hour before
Area Forecast Discussion
National Weather Service Medford OR
249 PM PST Sat Dec 11 2021
.SHORT TERM...Rest of today through Monday night...The start of a
very wet and much colder pattern is underway today. A potent front
is currently pushing through the region this afternoon, bringing a
plethora of impacts, including strong winds, heavy rain and
significant snowfall above 4000 ft. This is the first of two
impactful systems during the short term period and impacts from this
first front are expected to continue through tonight and into Sunday
morning. The current front slows and stalls across the southern
portions of the forecast area Sunday morning as the upper level
parent low digs deeper offshore Sunday. This will bring a relative
lull in the intensity of precipitation, with only lighter amounts of
snow and rain expected. Then, late Sunday night into Monday, a
secondary front swings through the area, bringing lowering snow
levels, reinvigorating precipitation intensity and increasing winds
again, though not as strong as today's system.
Strong winds have been recorded across the area today with gusts of
40 to 60 mph occurring at the typically windy areas (Weed, Summer
Lake, and along the Coast) and winds are starting to increase in the
more sheltered areas (southern end of Rogue Valley) and into the
Klamath Basin. Winds will peak in intensity late this afternoon into
the evening, then gradually diminish overnight into Sunday. Moderate
to heavy precipitation will continue into Sunday morning, with
significant snowfall expected generally above 3500 ft. By late
Sunday morning, one to two feet of snow is expected to accumulate
along the Cascades and Siskiyous as well the Marble Mountains of
western Siskiyou County. Up to a foot of snow is also expected in
the Mt Shasta City area as well as along the Hwy 97 corridor north
of Chiloquin. Winter Weather Advisories also cover portions of the
Klamath Basin into the higher terrain to the east. For more details
regarding amounts and timing, please see WSWMFR.
As previously mentioned, there will be a relative lull in the action
on Sunday as most of the energy and moisture moves south and the
front stalls over the southern portions of the forecast area and
weakens. However, light precipitation will continue with an
additional 1 to 3 inches expected for elevations above 3500 ft.
Breezy to gusty winds will continue through much of Sunday for the
Shasta Valley and across the East Side, diminishing by Sunday
evening.
This relative break in the weather will be short lived as a
reinforcing cold front will push through the region Sunday night
into Monday. Winds will increase again for the typically windy
spots, though aren't expected to be as strong. Snow levels will
lower with this secondary front, likely down to 2000-2500 ft.
Another one to two feet of snow is expected late Sunday night
through Monday in the same areas as are being affected today. Given
the relatively short break in the weather on Sunday, the current
winter headlines were extended through into Monday night. Additional
headlines will likely be needed for moderate to heavy snow down to
2500 ft for this time frame, including the Kalmiopsis region and
foothills of Jackson County late Sunday night through Monday.
If you have travel plans today through Monday night, be sure to keep
up with the most recent forecasts as wintry travel impacts will be
significant in some locations. /BR-y
.LONG TERM...Tue 14 Dec through Sat 18 Nov 2021.
The extended forecast looks cold and wet.
Strong southwest flow aloft will be in place Tuesday with a cold and
deep long wave trough just off the west coast. This trough will move
onshore Tuesday and will break to the east of the Medford forecast
area Tuesday evening.
The associated front will already be to the east of the area Tuesday
morning, and post-frontal showers will gradually diminish, but not
end completely, until the trough departs the area. It will be quite
cold and snow levels will drop to some west side valley floors
Tuesday, but precipitation will be very light or stopped by that
time, and amounts in the west side valleys will be 0.1 inches or
less.
There will be a brief period of short wave ridging behind the trough
Tuesday night into Wednesday , but a strong short wave sliding down
the back side of the trough will dig another trough offshore
Wednesday night into Thursday. This will push the next front onshore
Wednesday. The heaviest precipitation will occur Wednesday into
Thursday morning, with the heaviest precipitation occurring where it
usually does with southwest flow aloft, from the Kalmiopsis south
and east through western Siskiyou county into the Mount Shasta area.
Snow amounts in those areas look to be 1 to 2 feet during this time
frame. With the cold air already in place in the west side valleys,
overrunning flow will create a greater chance of snow there
Wednesday. Most of the heavy snow events in the west side valleys
occur with this pattern, but the pattern occurs a lot more often
that the heavy snow events. The models suggest up to 0.5 inches of
new snow is possible, but this event bears watching.
That trough will move onshore Thursday afternoon, then move out to
the southeast Thursday night. There won't be much in the way of
ridging behind that trough either, as yet another short wave will
follow Saturday. That one will be weaker though. At this time, it
looks like showers will diminish Thursday night, and Friday will be
mostly dry. Precipitation associated with the next system will start
to ramp up Friday night.
&&
.AVIATION...12/00Z TAFs...Widespread precipitation, MVFR/IFR
conditions, and terrain obscurations are expected through this
evening as a strong front pushes through the region. Low level
wind shear will be a concern at KOTH, KRBG, and KMFR until the
front passes. Freezing levels ahead of the front should hover around
4000-4500 feet. Once the front moves through late this afternoon
and evening, widespread MVFR cigs with areas of IFR cigs/vsbys in
low clouds and showers will develop with higher terrain obscured,
and freezing levels are expected to drop to around 2500 feet. The
lower conditions will persist through Sunday morning.
East of the Cascades...As the front moves through the region, MVFR
conditions with areas of IFR conditions in low clouds and snow will
develop this evening and persist through Sunday morning. Low
level wind shear and significant areas of mountain wave turbulence
are expected until the front passes. -BPN
&&
.MARINE...Updated 200 PM PST Saturday 11 December 2021...A strong
cold front will produce south gales and very steep, wind-driven seas
through this afternoon. Once the front passes, winds will shift
southwest and diminish. However, very steep seas will persist
through Monday. Long period west to northwest swell builds into the
waters this afternoon, peaking late Sunday afternoon into early
Monday morning. A weaker front will move onshore Sunday night into
Monday. Low pressure will remain over the area Monday into
Wednesday, then another front will move onshore Wednesday. Another
round of moderate westerly swell will build Wednesday night and
subside Thursday. -BPN
&&
.BEACH HAZARDS...Updated 200 PM PST Saturday 11 December 2021...A
high surf advisory remains in effect beginning 4 PM PST today and
lasting through 4 PM PST Monday. An incoming long period high WNW
swell will produce breaker wave heights of 20 to 25 ft, creating
hazardous surf conditions at area beaches this evening
through Monday evening. These large breaking waves will create
hazardous conditions along and within the surf zone, and could
inundate beaches and low lying shorelines. Beach erosion is
possible, and exposed infrastructure may be damaged. Jetties, rocks,
and logs are not the places to be in these situations, stay far away
from them.
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 10 PM PST Monday for ORZ028>031.
Winter Storm Warning until 10 PM PST Monday for ORZ027-030.
High Wind Warning until 10 AM PST Sunday for ORZ031.
Wind Advisory until 10 AM PST Sunday for ORZ031.
High Wind Warning until 4 PM PST this afternoon for ORZ021-022.
High Surf Advisory until 4 PM PST Monday for ORZ021-022.
Winter Storm Warning until 10 PM PST Monday above 3500 feet in
the for ORZ025.
CA...Winter Weather Advisory until 10 PM PST Monday for CAZ083>085.
High Wind Warning until 10 AM PST Sunday for CAZ085.
Wind Advisory until 10 AM PST Sunday for CAZ085.
Winter Storm Warning until 10 PM PST Monday for CAZ080-081.
Winter Storm Warning until 10 PM PST Monday for CAZ082-083.
Wind Advisory until 7 AM PST Sunday for CAZ081.
Pacific Coastal Waters...
High Wind Warning until 4 PM PST this afternoon for PZZ356.
Gale Warning until 10 PM PST this evening for PZZ356-376.
Hazardous Seas Warning until 4 PM PST Monday for
PZZ350-356-370-376.
MNF/JRS/BPN