High Wind in Oregon, January 11 to 12, 2024

Area Forecast Discussion
National Weather Service Medford OR
305 PM PST Thu Jan 11 2024

.SYNOPSIS...A high impact winter storm will arrive Friday and
persist through Saturday. Major impacts are anticipated in the
high Cascades as snow levels rise into the weekend. The forecast
could still change based on the surface low's trajectory.

.SHORT TERM...

Showers remain ongoing west of the Oregon Cascades this afternoon
with some pretty weak returns on radar. Surface stations have
reported a lighter drizzle under these showers, so they're not
putting out a ton of precipitation. Like earlier this morning,
shower coverage to our south is non existent. That trend will
continue through tonight into early Friday as models want to keep
things drier to the south. With regards to snowfall in the
Cascades tonight, snowfall is anticipated to ramp up late under
some favorable orographic lift. 850 mb winds remain close to
perpendicular to the terrain and about 25 to 30 knots. An
increasing plume of moisture will also likely contribute to the
increasing snowfall later tonight. Snow levels will star out
around 2500 feet before gradually rising to 3000 feet later in the
day on Friday.

As for Friday, the theme really doesn't change much with the
Cascades feeling the brunt of this snow event. Heading later in
the day, a surface low out in the Pacific and warm front will
push towards the Oregon coast late Friday evening into Friday
night. Farther towards our North east, a very cold airmass in
north east Oregon will push south, although struggle to really
impact our area except for a few caveats. All these synoptic
features will bring us some very favorable vertical lift Friday
night into Saturday morning. Snowfall rates should be fairly high
during this period. Snow levels vary from 1000 feet around Fort
Rock to up to 7000 feet in Brookings. In general, the winter storm
conditions will cover elevations generally above 3500 to 4000 feet
with some snow accumulation on the valley floors east of the
Cascades.

As for one of those caveats of colder air impacting us, there is
about a 20 percent chance for some freezing rain in north western
sections of Douglas and northern sections of Coos County near
Scottsburg and Elkton around highway 38. This is due to some of
the colder air seeping into valleys near the surface and warmer
air moving in aloft ahead of the surface low. Changes to the
surface low location farther north our south will impact these
probabilities. A coworker pulled up a gridded sounding from the
NAM and it showed a warm layer of around 6C and sub freezing
temperatures, so there are likely a small subset of models showing
freezing rain. We opted not to issue a winter weather advisory at
this point due to the current low probabilities, but that could
change if we gain more confidence in the freezing rain scenario.

Heading back to the snow winter weather impacts Saturday into
Saturday night, models keep the snow accumulation going in the
Cascades. The winter storm severity index that the weather
prediction center developed suggests extreme winter impacts due to
snow accumulation over the higher Cascades. This is indeed a lot
of snow in the forecast over the next 48 hours. We currently have
48 inches in the forecast for Crater Lake. Taking the 10th% NBM
snow accumulation forecast, which would be a fairly pessimistic
forecast, still produces up to 2 feet of additional snow fall over
that location.

As the surface low moves eastwards, a lot of vertical motion and
upwards lift will produce a little more snow east of the Cascades
than what we usually see it seems with these storms. Lakeview and
Chemult currently have an additional 16 inches of snow in the
forecast with Klamath falls seeing about 4 to 6 inches.

Finally, winds will be a concern in the Shasta valley with this
storm. There is a strong pressure gradient around 8 and 10 mb developing
as this surface low barrels into the coast. Winds aloft are not
exactly what we want to see for higher winds there, but there is
enough potential we decided to issue a high wind watch there for
Saturday. Models are not anticipating a lot of snow making it
into the Shasta valley, so we decided to issue a high wind watch
versus a winter storm warning.

The last topic we wanted to mention is the flood watch on the
Coquille river near Coquille. The latest hydrograph has the river
reaching minor flood Sunday due to all the precipitation the
region is going to see, and has already seen this week. Impacts
are anticipated to be minor with a few roads covered in low lying
areas. Sometimes this river is very slow to come down from a minor
flood warning, so this flood warning could very well linger into
Tuesday early next.

-Smith

.LONG TERM...Sunday 1/14 through Thursday 1/18...The long term
forecast will begin with a relative break in the weather as the
showers taper off as a ridge builds into southern Oregon and
northern California. This ridge will allow temperatures to be cold,
and we will need to stay on the lookout for potential freezing
temperatures at the coast, particularly in Coos County for Sunday
night. Otherwise, temperatures will rebound relatively quickly and
will be near normal, if slightly below normal.

During this break in rain, we will also need to monitor river rises.
For instance, guidance is starting to suggest that both forks of the
Coquille River as well as the Coquille River at Coquille could at
least enter action stage. Will need to continue monitoring this
situation to see if minor flooding is possible. If conditions
continue to warrant, we will likely need to issue river flood
watches in the next day or two. However, the break in rain suggests
that any river flooding should be relatively short-lived.

Then, the next system looks to arrive Tuesday night into Wednesday.
This could provide additional rain and snow. Details of this system
are uncertain, but snow levels appear to start off around 3000 feet
and rise to 6000 feet as the precipitation arrives. These details
will ultimately change in the coming days, so it will remain prudent
to continue monitoring the forecast.

Another ridge tries to build in on Thursday, but this may be short
lived. Ensemble guidance is all over the place, so have gone with
the national blend of models which is seeming to average the
precipitation chances over time. As we approach, expect the forecast
to denote breaks in precipitation as associated with these brief
ridges. -Schaaf

&&

.AVIATION...11/18Z TAFs...Isolated showers will continue to move
across the region today, especially over Coos, Curry, and Douglas
counties as well as over the south OR Cascades. With snow levels
around 1,200-1,500 feet this morning, mixed rain and snow showers
are possible down to the valley floor in Jackson County, while rain
remains the dominant precipitation type along the coast and in the
Roseburg area. Little to no snow accumulation is expected, and
impactful snow will continue to be concentrated around the Cascade
mountains. Freezing levels will rise some throughout the day,
reaching around 2500 feet by this evening. Widespread terrain
obscuration is also expected.

This evening and tonight, cloud cover is expected to diminish
across most areas, with the exception of the coast, the Umpqua
Basin, and the western slopes of the Cascades, and those areas that
see clearing overnight could quickly fog in. So while VFR/MVFR is
expected to prevail, areas of IFR/LIFR are possible in area valleys,
including at KMFR and KLMT by sunrise. -BPN
precipitaion
&&

.MARINE...Updated 200 PM Thursday January 11, 2024...West
to northwest winds and steep northwest swell will persist, but
gradually diminish through tonight.

Winds will shift to the south Friday ahead of the next system
arriving Friday night into Saturday. This system will bring a period
of gusty south to southwest winds and steep to very steep seas. An
increasing number of model solutions are showing very strong
pressure differences along the coast which would result in strong,
gale force winds and very steep seas across almost all of the
southern Oregon coastal waters. The strength of these winds, and the
location of the strongest winds, all depends on the precise track
and strength of the surface low, which could come ashore as far
north as the Columbia River, or as far south as Cape Blanco. Current
thinking is that there will be a hard roughly east to west boundary
somewhere between Reedsport and Newport, with strong southerly winds
to the south and cold and gusty east winds to the north. Due to the
high uncertainty, did not upgrade the current Gale watch, but
instead expanded it to all areas late Friday into Saturday, and will
await better consensus amongst the models before upgrading.

Winds will shift back to the NW later Saturday, then become more
northerly Saturday night into Sunday. After the low moves inland,
steep WNW swell will persist the remainder of the weekend. The
pattern calms down behind the weekend system, with improved
conditions expected for the first half of next week. -BPN

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 10 PM PST this evening above 2500
     feet for ORZ025.

     Winter Storm Warning from 10 PM this evening to 10 PM PST Friday
     above 3000 feet for ORZ025.

     Winter Weather Advisory until 10 PM PST this evening for ORZ027-
     028.

     Winter Storm Warning from 10 PM this evening to 10 PM PST
     Saturday for ORZ027-028.

     Winter Storm Warning from 4 AM Friday to 10 PM PST Saturday
     above 4500 feet for ORZ029>031.

CA...Winter Storm Warning from 4 PM Friday to 10 PM PST Saturday
     above 4500 feet for CAZ080.

     High Wind Watch from Saturday morning through Saturday evening
     for CAZ081-082.

     Winter Storm Warning from 4 PM Friday to 10 PM PST Saturday
     above 3500 feet for CAZ082.

     Winter Storm Warning from 4 PM Friday to 10 PM PST Saturday for
     CAZ083>085.

PACIFIC COASTAL WATERS...Small Craft Advisory until 10 PM PST this
     evening for PZZ356-376.

     Gale Watch from Friday evening through Saturday afternoon for
     PZZ350-356-370-376.

     Small Craft Advisory until 7 PM PST Friday for PZZ350-370.

&&