High Wind in California, November 13, 2020

Area Forecast Discussion
National Weather Service Medford OR
443 AM PST Fri Nov 13 2020

.DISCUSSION...The latest satellite image clearly shows a strong
frontal system knocking on our doorstep. Winds are cranking up along
the coast and offshore with strong winds expected this morning. last
hour North Bend was gusting to 51 mph and Gold Beach at 62 mph.
The general consensus is for winds to diminish along the coast as
the front moves onshore which is expected to occur late this
morning at which point winds will shift from the south to west.
Meanwhile moderate to strong winds are likely inland with the
strongest winds along and east of the Cascades with high winds
likely in the higher terrain this morning through this evening.
Also winds west of the Cascades, especially in the higher terrain
in Josephine and Douglas county and also the Illinois Valley will
be moderate to strong through this afternoon. Right now, southwest
winds are funneling through the Illinois Valley with gust to 22
mph. The only change to the wind headlines was to end the high
wind warning for the coast at 10 am pst because the front will
already have pushed inland and winds will shift west and diminish.
Please see NPWMFR for more details.

Rain will be heaviest along the coast, coastal mountains and
Cascades (below the rain/snow line) through this afternoon, then
rainfall rates will decrease tonight as we get into a post frontal
shower regime. 24 hour rainfall totals from 4 am pst Friday until 4
am pst Saturday) are expected to be between 1-2 inches for the
coastal mountains and Cascades, 0.50 of an inch to 1.0 inch for the
Umpqua Basin and 0.30 to 0.75 of an inch in the Rogue Valley. The
east side could also get their fair share of precipitation, but less
then the areas noted above. Even then some areas could get between
0.25 and 0.50 of an inch of rain.

Heavy snow will be a significant concern with this system due to a
very moist onshore flow and upper level dynamics. Heavy snow of 1 to
2 feet is expected along the Cascades for elevations of 5000 feet
and higher and especially near Crater Lake and Diamond Lake areas.
Highway 140 near Lake of the Woods could pick up 6-12 inches and 5
to 10 inches is expected over Mount Ashland. Snow levels may
fluctuate during the day, starting out around 4000 ft in the
morning, briefly rising above 5000 ft in the afternoon, then
lowering to 4000 ft Friday evening and night. Snow showers will
decrease in coverage and intensity late this evening into tonight.

In the Cascades, in addition to the heavy snow will be strong gusty
winds. Exposed areas in higher portions of the Southern Oregon
Cascades, such as Crater Lake, are expected to see winds gusting to
50 to 60 mph. More protected areas will still see winds gusting into
the 30 to 45 mph range. Strongest winds and heaviest snow are
expected late this morning through this evening. The combination of
strong gusty winds winds and heavy snow will bring extremely
dangerous winter storm conditions to the higher mountains in the
Cascades with the potential for extensive tree damage. White out
conditions may occur. Roads may be impassible at times.

East of the Cascades heavy snow is expected in the Chemult area and
the higher mountains in eastern Klamath and western Lake Counties
with around 6 to 10 inches in these areas. Areas of moderate snow
accumulations are expected south of Chemult into the Klamath basin.
Snow levels are expected down to valley floors, rising to around
5000 to 5500 in the late afternoon then lowering back down in the
evening. Winter storm warning and winter weather advisories remain
in effect for the areas noted above.

In Northern California, the main area of concern for heavy snow is
the in the Mount Shasta area where snow levels are expected to be
lower ahead of the frontal passage. Heavy snow is expected above
4000 feet in the Mount Shasta area with heavy snow impacting areas
of Highway 89 near Snowmans summit and over the higher terrain.
Strong gusty winds are expected in these areas as well with
strongest wind above 5000 feet. So expect periods of blowing snow
and near white out conditions for these areas. Also wet snow
combined with strong gusty winds may result in trees down. For areas
below 4000 feet, moderate snow is expected late this morning into
this afternoon. Snow levels are expected to start out low around
3000 feet then rise between 3500 and 4000 feet this afternoon. Given
the trend towards models showing lower snow levels, expect moderate
wet snow accumulations of 3 to 6 inches down to 3000 feet in the
Mount Shasta City area and along the I-5 corridor between Weed and
Dunsmuir. Please see the WSWMFR for all the details on the winter
storm warning and winter weather advisories.

We'll catch a brief break in the action tonight into Saturday
morning, then a warm front will move through late Saturday morning
bringing moderate rain to the Coast Range and Cascades. Amounts will
range from 0.5" to 0.75". Some rain shadowing is expected for the
Rogue valley and rain amounts will barely reach a tenth. Another
round of gusty winds is expected along the coast from Cape Blanco
north Saturday afternoon and evening.  Gusty winds are likely along
the ridges and peaks, as well as all areas east of the Cascades
Saturday afternoon and night. Snow will be less of an impact, with
snow levels rising from around 3500 feet to 4500-5000 feet.

A cold front will move into the area Saturday night and there is
some indications the front could slow down and stall over the area
Sunday through Sunday night which would lead to a prolonged period
of precipitation. The front is then expected to lift north Monday
morning and we could actually catch a break in the weather with dry
and milder weather from late Monday morning through Monday
afternoon.

Another low will track towards the Oregon coast after Monday.
Variability in the timing remains. The operational GFS shows the
front arriving Monday night while the Operational ECMWF shows the
front arriving mid to late morning Tuesday at the coast. The
majority of the individual ECMWF ensemble members are in similar
agreement with the operational ECMWF. Meanwhile the GEFS shows a
more progressive pattern which is in line with the operational GFS.

Other than the timing of when the front moves back, a progressive
pattern is in the works for most of next week with a series of
storms moving through the region. It all comes down to the timing of
each one of these. -Petrucelli

&&

.AVIATION...For the 13/12Z TAFS...
The strong frontal system moving in from the west this morning is
resulting in strong winds over and through the terrain this morning,
surfacing just inland from the Coast Range from about Interstate 5
in Oregon westward to the coast and over the coastal waters.
Precipitation with snow levels currently in the th 3500 to 4500 foot
range is surely resulting in icing across the area. The frontal will
move onto the coast this morning and then across inland areas today
leading to ceilings and visibilities reduced into the MVFR to IFR
range, precipitation, and terrain obscurations.

Precipitation is likely to begin as snow across much of the east
side, to include KLMT before mixing with or turning to rain before
turning back to snow late this afternoon and evening.

Wind shear is expected through the morning ahead of the front.
~BTL/DW

&&

.MARINE...Updated 430 AM PST Friday, 13 Nov 2020...
Gale force winds in the southern waters and storm force winds in the
vicinity of Cape Blanco northward appear to be occuring per
observations this morning. Seas are building rapidly from south to
north due to the strong winds, with square 6 foot seas at Buoy 27
building to 20 feet at 9 seconds at the Umpqua Offshore Buoy 229.
Winds and seas are expected to peak this morning. By this afternoon
westerly winds are expected with showery conditions. Heavy northwest
swell will follow, building this afternoon, peaking this evening
into tonight, and then continuing Saturday. Another frontal system
will bring another round of gales Saturday afternoon and evening.
The active pattern will then continue next week with several fronts
that could be significant, including the possibility of another
episode of very high 15 to 25 foot seas on Tuesday. However, the
details of when and how high winds and seas will peak next week
remains vague due to run to run variability in the numerical models
due to the fast flow across the region. ~BTL

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning until 10 PM PST this evening for ORZ030-031.
     Winter Weather Advisory until 1 AM PST Saturday below 5000 feet
     in the for ORZ030-031.
     Winter Storm Warning until 1 AM PST Saturday above 5000 feet in
     the for ORZ030-031.
     Wind Advisory from 10 AM this morning to 10 PM PST this evening
     for ORZ031.
     High Wind Warning until 10 AM PST this morning for ORZ021-022.
     Wind Advisory until 2 PM PST this afternoon for ORZ023-024.
     Winter Storm Warning until 4 AM PST Saturday above 5000 feet in
     the for ORZ027-028.
     Winter Weather Advisory until 1 AM PST Saturday for ORZ029.

CA...High Wind Warning until 10 PM PST this evening for CAZ085.
     Wind Advisory from 10 AM this morning to 10 PM PST this evening
     for CAZ084-085.
     Winter Weather Advisory until 4 PM PST this afternoon above 3000
     feet in the for CAZ082.
     Winter Storm Warning until 10 PM PST this evening above 4000
     feet in the for CAZ082.
     Wind Advisory until 7 PM PST this evening for CAZ081.

Pacific Coastal Waters...Gale Watch from Saturday morning through Saturday evening for
     PZZ350-356-370-376.
     Storm Warning until 10 AM PST this morning for
     PZZ350-356-370-376.
     Gale Warning until 10 AM PST this morning for PZZ356-370-376.
     Hazardous Seas Warning from 10 AM this morning to 4 AM PST
     Saturday for PZZ350-356-370-376.