High Wind in Oregon, January 4 to 5, 2023

Area Forecast Discussion
National Weather Service Medford OR
424 AM PST Wed Jan 4 2023

.DISCUSSION...A strong system is approaching the coast this
morning, and this will bring widespread strong winds to the area
today into Thursday. Surface low pressure offshore is deepening,
and this will increase the pressure gradient as it moves eastward
late this morning and tracks northward along 130W this afternoon
into Thursday. Pressure gradients are still expected to peak in
the -6 to -9 range for MFR- RDD and for OTH-ACV. This combined
with 700 mb flow in the 60-80 kt range, supports the concern for
warning level winds along the Coast, in the Shasta Valley and
portions of the East Side. Various wind headlines are in effect,
including High Wind Warnings along the Coast, in the Shasta Valley
and the higher terrain east of the Cascades where gusts of 60 to
75 mph are expected. In addition, strong winds are expected across
the terrain west of the Cascades as well as the lower elevations
east of the Cascades and the orientation of these winds will
equate to strong winds in the Rogue Valley as well. Wind
Advisories are in effect for these locations and details can be
found at NPWMFR.

As far as precipitation goes, warm advection precipitation will move
northeastward across the area this morning and afternoon. Amounts
will be light with this initial round of precipitation. After this,
the remainder of the event will largely be a Siskiyou County system,
though periods of heavier rainfall are also expected in Curry and
western Josephine counties. For the remainder of the area, however,
since the flow will be so strong and largely from the south, that
will mean lots of downsloping and a lot less precipitation.

Southerly upslope flow will be very strong for an extended period in
the Mt. Shasta region, so there will be plenty of rain/snow there.
Snow levels initially as precipitation arrives will be around 3500
feet, but are expected to rise to 4500-5500 feet this evening before
the height of the precipitation tonight into Thursday. Right now, it
looks like 2-6 inches of snow for areas along I-5 south of Weed,
before a changeover to rain. Heavier wet snow (6-8 inches) is
possible along Highway 89 near Snowman Summit west of McCloud before
the changeover to rain occurs there late tonight. The vast majority
of snow accumulation from this system will occur above 5000 feet, so
expect lots of fresh snow at Mt. Shasta ski area. With the
changeover to rain expected in the Shasta region and wet ground from
previous storms, there could be some localized flooding down there
since liquid precipitation amounts are likely to be in the 2-4 inch
range.

Conditions should begin to improve late Thursday afternoon as winds
weaken, however, gusty winds will continue well into the evening
with showers continuing overnight. We'll catch another break in the
weather early Friday, but additional systems are expected through
the weekend and into next week. /BR-y

LONG TERM (from the Tuesday afternoon AFD)...Friday through
Tuesday...It'll remain very active across the area late this week
and into early next week. Multiple fronts will move onshore during
this time period resulting in several rounds of wind, rain and high
elevation snow. In many ways, we'll be repeating the pattern from
midweek again and again, resulting in periods of strong winds at the
coast, the Shasta Valley, portions of the Rogue Valley and over the
East Side. While some beneficial rain/snow will affect areas in
Oregon, especially the coast ranges of Curry/western Josephine
counties, the focus for precipitation will be dialed into NorCal,
primarily Siskiyou County. Right now, we are not expecting
widespread flooding in Siskiyou County, but with multiple periods of
rainfall, we'll see significant rises on area streams, creeks and
rivers. So, definitely something to watch out for in the days ahead.
Of course, much of this precipitation is needed to put a dent into
the 3+ year drought, just hopefully not at the expense of flooding.

The upper pattern on Friday will feature a ridge axis overhead in
the morning, which will shift to the east in the afternoon allowing
a front to move onshore late Friday and Friday night. Many areas
will probably escape with a dry day, but rain could arrive at the
coast in the afternoon. This one appears fairly weak, but could
result in some breezy winds and some light rain/snow.

A more robust system could develop late Friday night into Saturday
and move northward along or just inside 130W, bringing the potential
for another round of significant wind area wide, and precipitation
focused in Siskiyou County, particularly the Shasta region. There is
quite a bit of variability in the guidance with respect to the
strength/position of the low moving northward offshore, ranging from
a fairly weak non-deepening low farther offshore, to a stronger,
rapidly deepening one closer in to the coast. So, there will likely
be changes to this portion of the forecast. Either way, however, it
does appear stronger than Friday's front. Wind products for the
usual areas will probably be needed. But, once again, snow levels
will mostly stay near or above 4500 feet resulting in snow impacts
mostly near or above the main passes along I-5/in the Cascades. The
snow level could dip to 4000 feet at times. Snow could once again be
measured in feet above 5000 feet in NorCal. Additional moderate to
heavy rainfall is likely in the Shasta region below 4500 feet.

The winds and precipitation could last into Sunday, but we do expect
a break Sunday night into Monday before the next system follows a
similar path as its predecessor Monday afternoon into Tuesday.
-Spilde

&&

.AVIATION...04/12Z TAFs... IFR/LIFR fog has covered the valleys this
morning ahead of the next system. Winds are being observed tonight,
so this fog might be up and down for the remainder of the overnight
hours.  Eventually, rain will move into the region with VFR ceilings
becoming more likely through the day.  Look for visibilities falling
to 3 to 6 miles as some of the rain moves through.  Wind shear will
also be a problem, especially along the coast as this system moves
in. Surface winds may also pose an issue later this afternoon as
wind gusts reach up to 40 knots over KLMT.

Fog seems unlikely within many of the valleys west of the Cascades
Wednesday night as strong winds persist overnight.

&&

.MARINE...Updated 400 AM PST Tuesday 3 January 2023...

An exceptional storm will approach the area from the west-southwest
today with a strong front developing offshore. The system will then
track northward along the 130 west longitude off the Oregon and
Washington coasts through Thursday. A front is expected to move into
the waters later this evening with gale force winds increasing.
Storm force winds will move into the waters Wednesday night into
Thursday morning as the low tracks north.

When combined with continued very steep south wind seas and fresh
swell, seas will peak Thursday between 30 and 35 feet with the
highest seas farther from shore. Large breaking seas and
exceptionally dangerous bar conditions will occur. Very high and
very dangerous seas will then continue behind the front late
Thursday into Thursday night as a long period (15 to 17 second) west-
southwest swell builds into the region.

Yet another low will build up out of the south and strengthen as it
moves towards Canada around Friday.  Gale force winds are likely
during this period.  Beyond Friday, the weather looks very unsettled
with storms strengthening over the Pacific into next week.  The
period between storms systems look fairly brief.

-Smith

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning from 10 AM this morning to 4 PM PST Thursday
     for ORZ026.

     Wind Advisory from 4 PM this afternoon to 7 PM PST Thursday for
     ORZ029>031.

     High Wind Warning from 4 PM this afternoon to 4 PM PST Thursday
     for ORZ030-031.

     High Wind Warning from 10 AM this morning to 4 PM PST Thursday
     for ORZ021-022.

     High Surf Warning from 4 PM this afternoon to 10 AM PST Friday
     for ORZ021-022.

     Wind Advisory from 10 AM this morning to 4 PM PST Thursday for
     ORZ023>026.

CA...Winter Storm Warning until 10 AM PST Thursday above 4500 feet
     for CAZ080>083.

     Winter Weather Advisory until 7 PM PST this evening for
     CAZ081>083.

     High Wind Warning from 10 AM this morning to 4 PM PST Thursday
     for CAZ081-082.

     Wind Advisory from 4 PM this afternoon to 7 PM PST Thursday for
     CAZ083>085.

     High Wind Warning from 4 PM this afternoon to 4 PM PST Thursday
     for CAZ085.

PACIFIC COASTAL WATERS...Small Craft Advisory until 1 PM PST this
     afternoon for PZZ350-356-370-376.

     Storm Warning from 1 PM this afternoon to 7 PM PST Thursday for
     PZZ350-356-370-376.

&&

MNF/CZS/MAS