Winter Weather Advisory 32, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
928 AM PST Fri Dec 10 2021

.DISCUSSION...
No updates to the forecast are necessary this morning.

Some light rain and snow showers occurred overnight and continue
this morning. Snow amounts were as was expected, with 1-3 to
inches in the Oregon Cascades mainly north of Highway 140 and a
dusting, elsewhere, into the Siskiyous. Currently, there's some
light snow shower activity moving into the Cascades in eastern
Douglas County toward Crater Lake NP. These showers will continue
to taper off through this afternoon into early this evening, with
snow levels rising from around 2kft this morning to around 3kft
this afternoon.

A much stronger low pressure system will move in with wind, rain,
and snow above 3kft elevations Saturday, continuing into Sunday.
Multiple headlines are out for wind and snow for that weather
system, and we'll be updating those headlines and, likely, adding
some additional headlines today.

A cold, wet, and active weather pattern is then generally expected
to continue through the next 10 days. Some of our Winter Storm
Watch headlines currently go out through Tuesday. Stay tuned for
updates as we move into this more wintry pattern.

It is worth noting that December is, climatologically speaking,
one of our coldest and wettest months across the forecast area.
Since we're expecting it to be colder and wetter than normal over
the next 2 weeks, travel impacts are likely to be significant, at
times. Of course, this is good news for our water/drought
situation, though we have a very long way to go to break the
drought. More this afternoon... ~BTL

&&

.AVIATION...10/12Z TAFs...Along the coast and just offshore. Weak
instability into this evening will result in VFR conditions with not
much more than a few isolated showers. This evening and tonight, a
strong front will approach the area from the north resulting in
increasing south winds with gusts up to 30 kts. VFR ceilings are
expected to continue into tonight, but it will be a close call
towards the end of the TAF period.

Inland west of the Cascades, low clouds with LIFR ceilings are bring
observed in the Umpqua Basin, including Roseburg and Grants Pass
area, including Merlin. The TAF shows ceilings at Roseburg improving
to VFR at 21z, but there is a chance it could improve an hour or so
earlier. VFR ceilings are expected this afternoon until the end of
the TAF period. However, winds aloft will increase as a strong front
approaches resulting in low level wind shear at Roseburg and Medford
late this evening and tonight. Meanwhile, VFR ceilings are expected
at Medford through the TAF period. However, mountains are expected
to be partly obscured this morning.

East of the Cascades, VFR conditions are expected through the TAF
period with partial mountain obscuration possible until 21z.
-Petrucelli

&&

.MARINE...Updated 800 AM PST Friday 10 December 2021. Seas will be
steep and hazardous to small craft into this evening and will be
dominated by a northwest swell at 13 seconds.

South winds will increase this evening. An incoming front will bring
gale force south winds and very steep seas to the waters late
tonight into Saturday morning.

Winds will diminish, but very steep seas will persist over the area
after the front moves inland Saturday. Long period northwest swell
will build into the waters Saturday night into Sunday and peak
Sunday evening through Monday night at 16 to 19 feet at 16 seconds.
Another weaker front will move onshore Sunday. Low pressure and
steep seas will persist over the waters early next week, and yet
another front will move onshore Wednesday.

&&

.BEACH HAZARDS...Updated 800 AM PST Friday 10 December 2021. With
the incoming long period WNW swell, there is a risk for high surf at
area beaches Sunday morning through Monday evening. Breaker heights
in the surf zone are expected to reach 20 to 25 feet. The 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 are not the place to be in these situations, stay
far away from them.

&&

.PREV DISCUSSION... /Issued 404 AM PST Fri Dec 10 2021/

DISCUSSION...Lingering showers will taper north through the day,
with the bulk of the precipitation on the coast and coastal
ranges, and the Cascades. With a cold air mass in place with the
northerly winds aloft snow levels will remain low affecting all of
the northern Cascade passes, but snow amounts will be light.

The next system still looks to be strong as we head into Saturday.
As the front approaches the coast strong southerly winds are
expected at the coast and the High Wind Watch has been upgraded to
a warning for portions of the coast for Saturday. These strong
winds will spread inland to the east side later in the morning and
the High Wind Watch has been upgraded to a warning for some areas
east of the Cascades for Saturday into early Sunday morning. Wind
advisories may be needed for some lower elevation areas of the
east side as well. The gradient in the Shasta Valley increases
Saturday as well, but the 700 mb winds are almost due westerly, so
high wind warning winds are not likely, but advisory winds may be
possible.

The strong westerly 135 kt upper jet moves south over the region
Saturday afternoon bringing the heavier precipitation into our
region. Winter storm watches remain for much of Siskiyou County
as well as the Oregon Cascades and Siskiyous for 10 to 20 inches
of snow, with possible locally higher amounts, for Saturday
afternoon through Sunday afternoon. Snow levels are likely to be
in the 2500-4500 foot range during this time period and heavy, wet
snow is likely in the Mount Shasta area. The Nam12 is indicating
possible lower elevation snow at times in the Mt Shasta area, and
snow levels may drop down even lower at times.

Winter storm watches in NorCal remain through Monday for western
Siskiyou County, and through Tuesday afternoon in the Mount Shasta
area as another wave of low pressure moves through the area and
focuses on Northern California. Snow levels Sunday night into
Monday are likely to rise a bit, into the 3000 to 4000 foot
range, and snow could, therefore, change to rain for some of that
time period in and near Mount Shasta City. Stay tuned for updates
on this. Also, additional significant snowfall is likely in other
areas of SW Oregon through Tuesday, though the focus of the
heaviest snow is likely to remain in the Mount Shasta area.

Monday night through Thursday ensembles indicate the possibility
of a couple more low pressure systems, but have differed on the
details, especially related to how far inland moisture makes it
with cold temperatures in place. From Monday night through
Wednesday there is a possibility of impacting low elevation
snowfall for areas west of the Cascades, to include the lower
valleys of Jackson and Josephine counties. -Sven

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning from 4 AM Saturday to 10 AM PST Sunday for
     ORZ030-031.
     Winter Storm Watch from Saturday morning through Sunday
     afternoon for ORZ025-027-028-030.
     High Wind Warning from 4 AM to 4 PM PST Saturday for ORZ021-022.

CA...High Wind Warning from 4 AM Saturday to 10 AM PST Sunday for
     CAZ085.
     Winter Storm Watch from Saturday afternoon through Tuesday
     afternoon for CAZ082-083.
     Winter Storm Watch from Saturday morning through Monday evening
     for CAZ080-081.

Pacific Coastal Waters...
     High Wind Warning from 4 AM to 4 PM PST Saturday for PZZ356.
     Small Craft Advisory until 10 PM PST this evening for
     PZZ350-356-370-376.
     Gale Warning from 10 PM this evening to 4 PM PST Saturday for
     PZZ350-356-370-376.

BTL/SBN/MAP