High Wind in California, December 15, 2021

Area Forecast Discussion
National Weather Service Medford OR
836 AM PST Wed Dec 15 2021

.DISCUSSION...Forecast looks mainly on track this morning per the
latest data. Heavy snow will impact the Mount Shasta City area,
and with gusty south winds in the area, Interstate 5 will
experience periods of very low visibility later this morning into
the afternoon. Snowfall rates will likely be 1 inch+ per hour.

The lowest confidence portion of the forecast is in the Southwestern
Oregon valleys where we expect some snowfall in Josephine and
Jackson Counties this morning as temperatures hover around freezing.
Also, some south winds begin to pick up this morning and will likely
bump temperatures up some and keep precipitation lighter over
Jackson County than Josephine. We maintain a Winter Weather Advisory
over Josephine County above 1500 feet (Hayes Hill, Sexton Pass on I-
5) with an Advisory above 2000 feet for Jackson County. Snow levels
will likely rise during the daytime hours.

Please check out our previous forecast discussion which details this
front and expected impacts today into this evening. Keene

&&

.AVIATION...15/12Z TAFs...Conditions are expected to bounce between
VFR and MVFR because of weak showers. Low level wind shear is likely
to develop at airfields along the coast around 10Z and across the
interior west side around 12-15Z this morning and then persist
through about 20Z. Snow down to around 500 to 1000 foot elevations
during this morning is possible. Higher terrain will be obscured at
most locations. This afternoon into the evening snow levels are most
likely to rise into the 1500 to 2500 foot range at most locations
while IFR to MVFR in moderate snow showers will continue at other
locations.

An Airport Weather Warning for both wind and snow is likely to be
needed for KLMT for Wednesday, most likely in the daylight hours.
~DW/Miles

&&

.MARINE...Updated 815 AM PST Wednesday, 15 December, 2021...Strong
south winds are being observed as a strong front approaches the
waters. Buoy 15 reported a peak gust of 51 kts this pas hour.
Meanwhile the buoy's offshore are showing southwest winds behind the
front. The general consensus is for the front to move onshore late
this morning with winds shifting from south to southwest first over
the outer waters, then inner waters. Once the front moves onshore,
winds will shift to the southwest and gradually diminish. However
seas will remain very steep and hazardous with Hazardous Seas
Warning conditions expected from late this afternoon through tonight.

Seas peak around 15 to 18 ft at 8 to 9 seconds out of the south-
southwest late this morning. West swell will then build to another
peak with seas around 16 to 19 ft at 13 seconds late tonight. Swell
dominated seas will remain steep while they gradually subside
Thursday. Seas continue to diminish Friday ahead of a seasonably
strong front on Saturday. Gales are possible on Saturday.
-Miles/Petrucelli

&&

.PREV DISCUSSION... /Issued 408 AM PST Wed Dec 15 2021/

SHORT TERM...A strong front is approaching the coast early this
morning and will bring a round of moderate to heavy precipitation
to much of the area and strong, gusty winds.  Snow levels are
expected to start out low this morning as light precipitation
spreads into the area, around 1500 feet elevation, then snow
levels are forecast to rise to around 2000 to 2500 feet during
the day as southerly winds increase ahead of the front and
precipitation increases over the area.

Snow impacts: Many areas will see snow impacts as this storm
system moves through. We continue to have high confidence in
heavy snow impacting portions of Siskiyou County, including higher
terrain in Western Siskiyou, and the Mount Shasta area in
southern/southeastern Siskiyou County, including from Weed
southward and Mount Shasta eastward. A winter storm warning
remains in effect for these areas today through this evening. The
heaviest snow is likely late this morning through this evening.
Very heavy snow is expected to develop across the Mount Shasta
area, including along I-5 from Weed southward in southern Siskiyou
County. Additionally the combination of heavy snow and strong,
gusty winds is expected to bring near white out conditions at
times for areas near Weed today. Behind the front, snow will
continue for these areas in Siskiyou County. However expect
lighter snow accumulations with showers tonight and Thursday for
these areas.

Across southwest Oregon, moderate snow is expected
to impact some areas from the Cascades west including lower
passes such as Hayes Hill and Sexton Summit, as well as areas at
and above 2000 feet elevation in Jackson County and south/central
Douglas County and areas down to 1500 feet elevation in Josephine
and eastern Curry County. Observations support the forecast of
snow levels down 1500 this morning. Radar imagery shows very
light precipitation moving inland into western portions of the
area early this morning with a band of light to moderate
precipitation at the coast. Overall, models continue to
support the current forecast with very light snowfall possible in
many western valleys early this morning with the best chance for
light valley snow accumulations of around an inch or two in the
southern Illinois Valley. As southerly winds increase over the
area, models continue to support that snow levels will rise to
2000 to 2500 feet late this morning and into the afternoon. So
expect the main impacts for lower elevation snow to occur over the
lower passes near Hayes Hill, Sexton Summit and across the
foothills and mountains west of the Cascades. Please see the
WSWMFR for details on the winter headlines.

East of the Cascades, expect a sharp gradient from
significant, impactful snow to off and on snowfall with less
impacts. This will be right around Klamath Falls-- significant
snow to the north and much less so to the south. Windy conditions
will align with snowfall east of the Cascades to result in drifts
and very low visibility, and this will also be the cast near Weed
along Interstate 5 on Wednesday, with gusty winds, snow, and
occasional very low visibility.

Showers linger Thursday morning, with the Cascades likely seeing
additional snow accumulation.

Wind impacts: The strong frontal system will bring moderate to
strong winds over a good portion of the area this morning into
this evening.

Along the coast, guidance is pretty consistent showing pressure
gradients from Arcata to North Bend peaking out between 8 and 10 mb
Wednesday morning which typically results in high winds. Winds are
expected to be strongest for a 6 hour period mid morning through
early afternoon before diminishing during the afternoon after the
front moves onshore. The High Wind Warning (NPWMFR) has been
extended through 1 PM this afternoon for areas along the coast.

Moderate to strong winds will occur in the Shasta Valley with
winds strongest near Weed, beginning this morning and remaining
strong through late this afternoon. Pressure gradients between
Medford and Redding are expected to peak out around 8 to 10 mb
late this morning into early this afternoon. Winds are expected
to reach high wind warning criteria from about Yreka south along
I-5. Even though a separate high wind warning not has been issued
for that area, the details of snow and wind combined have been
outlined in the Winter Storm Warning and Winter Weather Advisory
for this area. Please see the WSWMFR for more details. Gusty winds
will continue into the evening, but at the same time will
gradually decrease as wind direction shifts southwest which
typically become less favorable for strong winds in this area.

At the same tine winds are in a favorable alignment (southeast) for
gusty winds to develop in the Rogue Valley this morning into early
this afternoon. Winds are expected to be strongest between from
mid morning until early afternoon, and some areas are expected to
reach advisory criteria. A Wind Advisory has been issued. Winds
should diminish once the front moves through by mid afternoon.

East of the Cascades, winds will start to increase during the
morning hours  with the strongest winds expected between noon and
5 pm pst. Models show 700mb winds peaking out close to 70 kts
early this afternoon and expect to reach High Wind Warning
criteria, especially over the higher terrain and along Highway 31
between Summer Lake and Paisley. Gusty winds will continue into
the evening, but the general consensus is for winds to peak in
the late afternoon then gradually decrease in the evening. Winds
will continue to diminish tonight, except for the ridges where
gusty winds could persist into the overnight hours. Please see
NPWMFR for more details on the wind headlines.

After today/tonight, winds are not expected to be a concern until
Saturday afternoon ahead of another potentially strong cold
front.

LONG TERM...Late Thursday through Tuesday...Some lingering snow
showers are expected across the Cascades with some light rain
possible in the Umpqua Basin late Thursday and Thursday night. The
area will see a break in the active pattern on Friday as high
pressure builds into the area. Then a weak warm front moves into
the area Friday evening into Saturday followed by a cold front
gradually moving across the area late Saturday into Sunday. Very
light precipitation with lower snow levels around 2000 to 3000
feet is possible for western portions of the area Friday evening
but snow levels are expected to gradually rise to 3500 to 6000
feet Friday night and early Saturday as light precipitation
spreads inland over areas west of the Cascades. Models have
trended slower on the timing of the cold front reaching the coast
on Saturday and current models favor the main band of
precipitation moving into western portions of the area late
Saturday and Saturday evening then gradually moving across the
area Saturday night and Sunday. Snow levels are expected around
4000 to 6000 feet from the Cascades west, lowering to 3000 feet
with the frontal passage Sunday morning. East of the Cascades,
expect snow levels to remain low as light precipitation moves into
the area with the front. Additional light showers are possible
over the area Sunday night.

Early next week, an active weather pattern continues as an upper
low sets up  just off the coast and a couple low pressure systems
offshore move into the area. -CC

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning until 7 PM PST this evening for ORZ030-031.
     Winter Weather Advisory until 1 AM PST Thursday for ORZ029>031.
     Wind Advisory until 7 PM PST this evening for ORZ029>031.
     High Wind Warning until 1 PM PST this afternoon for ORZ021-022.
     Winter Weather Advisory until 8 AM PST Thursday above 1500 feet
     in the for ORZ024.
     Winter Weather Advisory until 8 AM PST Thursday above 2000 feet
     in the for ORZ023-026.
     Wind Advisory until 1 PM PST this afternoon for ORZ026.
     Winter Weather Advisory until 10 AM PST Thursday for ORZ025.
     Winter Weather Advisory until 10 AM PST Thursday for ORZ027-028.

CA...High Wind Warning until 7 PM PST this evening for CAZ084-085.
     Wind Advisory until 7 PM PST this evening for CAZ084-085.
     Winter Storm Warning until 10 PM PST this evening for CAZ080.
     Winter Storm Warning until 10 PM PST this evening for
     CAZ082-083.
     Winter Weather Advisory until 10 PM PST this evening for CAZ080.
     Winter Weather Advisory until 10 PM PST this evening for CAZ081.
     Winter Storm Warning until 10 PM PST this evening for CAZ081.
     Winter Weather Advisory until 10 PM PST this evening for CAZ083.
     Winter Weather Advisory until 10 PM PST this evening for CAZ085.

Pacific Coastal Waters...
     Storm Warning until 1 PM PST this afternoon for
     PZZ350-356-370-376.
     Hazardous Seas Warning from 1 PM this afternoon to 4 AM PST
     Thursday for PZZ350-356-370-376.