High Surf in Oregon, January 7 to 8, 2023

Area Forecast Discussion...Update
National Weather Service Medford OR
437 AM PST Sat Jan 7 2023

Updated marine and aviation sections.

.SHORT TERM...Water vapor imagery is showing a stationary front
stretched out along the coast at this time. This front isn't
moving much since it is more/less parallel to broad upper level
southerly flow. A couple of low centers are expected to move
northward along this front this morning with most precipitation
expected from the Mount Shasta region north and west.

Downslope flow, however, into the west side valleys (especially
the northern part of the Shasta Valley and also the Rogue Valley)
will largely limit the amount of precipitation in those areas. In
fact, in just the last hour or so, winds have once again surfaced
here in Medford with a gust to 35 mph reported on KMFR ASOS and
the temperature subsequently jumping up to 53F (from 46F). Winds
aloft are strong enough today and tonight for lots of wind
headlines, mainly over inland areas, but with the strongest winds
expected in the Shasta Valley and also over the East Side. These
areas will have peak wind gusts in the 50-65 mph range. Since
925-850mb flow is more/less aligned with the Rogue Valley, we
expect advisory level wind gusts (45 mph) here again today.
Coastal areas will also get some wind, especially tonight into
Sunday morning, but strongest gusts there will probably in the
50-55 mph range.

The most persistent rain and snow will be in the Siskiyou County
mountains northwestward to the coast ranges of western Josephine
and Curry Counties and up along the coast. Southerly upslope flow
will be maximized from the Trinities over to Mt Shasta and the
Medicine Lake area. Snow levels are currently around 4500 feet,
with recent web cams at Snowman Summit along Highway 89 looking
snow covered. Along I-5, it's just rain at the moment. Overall, it
is expected to remain that way today, but some cooling later this
afternoon and especially tonight with a bout of heavier precipitation
will probably lower the snow level a bit, down to perhaps around
3500 feet. We've adjusted the winter headlines, opting to lower
the elevation to above 4000 feet in the Winter Storm Warning and
also add an advisory for areas in western Modoc County. This will
allow for a heavier period of snow to potentially impact I-5
tonight into Sunday morning as precip rates increase, especially
at Black Butte Summit. Overall, we are expecting 10 to 20 inches
of snow in the warning areas with snow measured in feet over the
mountains above Mt Shasta City. Hi-res guidance is indicating a
high potential (90% or greater) for snowfall rates of 1 inch per
hour tonight into Sunday morning for several hours in the
aforementioned area. OK, then, you might ask, how much snow will
occur in Mt. Shasta City? This is a tough question because most of
the guidance keeps the snow level above the city. NBM
probabilities of greater than 3 inches of snow right in the city
are less than 30%. The NAM12, however, which is one of the
coldest solutions, does show the snow level lowering to around
3000 feet. The thought is that rain does change to snow at Mt.
Shasta City tonight possibly resulting in a few inches by Sunday
morning with the temperature remaining just above freezing. This
is something we'll be keeping an eye on and we'll update the
forecast accordingly if we see a higher potential of occurrence.

After that, there is a very brief break Sunday afternoon/evening
before the next stronger front moves in Sunday night into Monday.
We'll probably need another round of wind headlines for that event
along with potential winter headlines again in Siskiyou County. We
shouldn't ignore the fact that the Cascades/Siskiyou Mtns will
also get some snow with these fronts, but amounts through early
next week should mostly be in the 6-12" range (perhaps a bit
higher above 6000 feet). -Spilde

.LONG TERM...(Monday through Friday). The pattern will remain
active for the foreseeable future with a parade of systems moving
the area. The pattern that has set up over the Pacific remains
fairly consistent with systems lined up as far west as the
Aleutians.

The main challenge during this time will be the timing, intensity,
and track of each individual upper low trough, surface fronts and
surface low pressures. The main change from what was discussed
yesterday are that there is better clarity among the operational
ECMWF, GFS and there respective individual ensemble members.

Right now it looks like Sunday nights/Mondays storm will be the
strongest of the lot in terms of precipitation and winds. Even then
the bullseye of the precip will be in northern California, and
perhaps the southern coastal range. These areas have the best chance
of getting moderate to occasionally heavy precipitation from Sunday
night into Monday afternoon, although precipitation could end up
diminishing Monday afternoon along the coast and south coastal
range.

Another weaker storm will be on the heels of Monday's storm and
impacting mostly northern California, however, precipitation
amounts are not expected to be as significant, and it should not
be as windy.

Snow levels during this time will fluctuate, especially during
periods of when the warm front moves through where they can end up
around 5000 feet, followed by the cold front where they could lower
to around 4000 feet. Areas above 5000 feet are likely to have some
travel impacts. Thats' not to day areas above 4000 wont't but the
chances will be diminished some.

We'll catch "relative" break in the action as short wave ridging
builds in Tuesday night into Wednesday, before the next system
arrives bringing increasing precipitation and gusty winds.

One thing to note: A large upper trough west of Wednesday's system
is expected to dig which could result in the bulk of the
precipitation to remain along the coast and offshore Wednesday night
through Thursday, then by the time it makes its way inland we could
see a flow split which typically puts a cap on the amount of
precipitation and less concern for wind.

There is "some" evidence supporting the continued wet and windy
pattern through at least the middle of the month, followed by a
pattern change for the latter part of the month with troughing
developing in the eastern part of the U.S. with riding building over
the Pacific Northwest. A different data set (showing the same
parameters) were not as convincing yesterday, but today it's showing
some promise. -Petrucelli

&&

.AVIATION...07/12Z TAFs...Conditions at all TAF locations will
remain fairly similar for the following 24 hrs. Strong south flow
aloft will remain over the region as deep low pressure remains
active over the Eastern Pacific. For the coast, a subtle increase in
the flow aloft tonight will allow for a developing low level wind
shear as near-surface winds remain offshore and fairly light. Clouds
cover should remain mainly VFR except for localized vfr fog briefly
this morning. Inland west side valleys, clouds will remain VFR with
areas of higher mtns obscured. Gusty surface winds will occur in
areas, including predominant at KMFR. East of the Casacdes gusty
south winds will remain dominant through the period with higher mtns
obscured but VFR. Stavish

&&

.MARINE...Updated 430 AM PST Saturday, January 7th 2023...South
gales will prevail this morning as a tight and compact low pressure
center moves south to north through the waters. Brief storm force
gusts are possible between 5 and 40 nm from shore between 5 am and 7
am. Winds ease but seas will remain hazardous this afternoon and
evening. Winds will again increase to Gale Force with another low
arriving later this evening through early Sunday morning. Conditions
improve slightly Sunday afternoon and evening, but yet another low
will allow winds to increase again Sunday night into early Monday.
Stavish

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 7 AM this morning to 10 PM PST this evening
     for ORZ029.

     High Wind Warning from 7 AM this morning to 4 AM PST Sunday for
     ORZ030-031.

     Wind Advisory from 7 AM this morning to 4 AM PST Sunday for
     ORZ030-031.

     Wind Advisory from 7 AM this morning to 4 AM PST Sunday for
     ORZ026.

CA...Winter Storm Warning until 10 AM PST Sunday above 4000 feet for
     CAZ080>083.

     Wind Advisory until 7 AM PST this morning for CAZ081.

     High Wind Warning from 7 AM this morning to 4 AM PST Sunday for
     CAZ081.

     Wind Advisory from 7 AM this morning to 10 PM PST this evening
     for CAZ084.

     High Wind Warning from 7 AM this morning to 4 AM PST Sunday for
     CAZ085.

     Wind Advisory from 7 AM this morning to 4 AM PST Sunday for
     CAZ085.

     Winter Weather Advisory from 4 PM this afternoon to 10 AM PST
     Sunday for CAZ085.

PACIFIC COASTAL WATERS...Gale Warning until 10 PM PST Sunday for
     PZZ350-356-370-376.

     Gale Watch from Sunday evening through Monday morning for PZZ370-
     376.

&&

MAS/MTS