High Wind in Oregon, December 25 to 26, 2024

Area Forecast Discussion
National Weather Service Medford OR
214 PM PST Wed Dec 25 2024

.DISCUSSION (Today through Tuesday)...

Overview:

Our active pattern continues across the forecast with impacts
likely through this weekend and into early next week. Our next
system is starting to move on shore today, and this will produce
widespread impacts from the coast through the Cascades and over
into the Eastside. Snow impacts will be mainly above 5000 feet,
but there is a short window of snow levels around 4000 feet down
around the Mount Shasta area and Marble Mountains early tonight.
Snow levels will quickly start to rise late Friday morning. Wind
speeds will be strong through Friday, so even light snowfall
amounts could cause at least some visibility restrictions on top
of hazardous road conditions. There will be another lull after
this system, but another system will be quickly on the heels of
this one, and we could see more wind, heavy rain, and snow impacts
across the forecast area through this weekend. We will need to
pay special attention to how rivers react to this system, so we
can hopefully get a better gauge on potential river flooding
expected this weekend. Please see the hydrologic outlook for
further information.

Further Details:

Current H5 trough and associated surface low over the Gulf of
Alaska are starting to impact the region early this afternoon
with light precipitation moving through the area. Precip intensity
will pick up this afternoon and will result in heavy rain
(especially along and near the coast) tonight, higher elevation
snow (mainly above 5000 feet), and wind impacts across the area.
The biggest uncertainty is how low will snow levels drop because
there is a short window of 4000 feet possible before precipitation
really starts to ramp up tonight. This means some areas (mainly
eastside) could see light snowfall amounts outside of the current
advisory, especially areas above 5000 feet that are not in the
advisory. Mount Ashland could see around 10-12 inches over 36
hours. Fairly decent probabilities (85%) for snowfall amounts
12.0" or greater in 24 hours for areas in and around Crater Lake.
Probabilities decrease south towards Lake of the Woods for a foot
or more of snowfall. Those areas around Lake of the Woods have a
10% chances of 12.0" or greater, but those probabilities increase
to around 40% for 6.0" or greater in 24 hours for areas around the
lake--all of which are a decrease from 24 hours ago for areas
around Lake of the Woods. A combination of mixing and the
pressure gradient will result in strong wind speeds near the coast
and midslopes/higher elevation of the eastside where a High Wind
Warning is in place. Gusts upwards of 70 mph will be possible in
locations of the High Wind Warning. Strong winds will result in
blowing snow and reduced visibilities during our snowfall windows,
and we could have two distinctive periods of peak snowfall rate
thanks to two different kicker lows coming out of the main
cyclonic flow. The first peak would be around 4am-8am tomorrow
morning when strong omega values exist within the dendritic growth
zone with elevated CAPE noted, albeit only around 50-100 J/kg.
The combination of instability and strong forcing could lead to
snowfall rates around 1.5" per hour. There could be another peak
Friday morning as well as another kicker wave comes out, but rates
would only be around 0.5" per hour for the second peak. Again,
wind speeds could create reduced visibilities, especially during
high snowfall rates, but it doesn't take much snow to create
visibility issues given the forecast wind gusts of 50-70 mph for
some higher elevations.

There will be another storm system this weekend with more rounds
of heavy rainfall, higher elevation snowfall, and wind hazards.
This next system over the weekend could be closely on the heels of
the current one, yet we could see much higher snow levels, so we
will need to monitor river rises from heavy rain and snow melt
through this weekend. After this week's parade of storm systems,
we are seeing signs of potential flooding for some our of rivers
and tributaries. A lot of uncertainty here with river forecasting.
We will be taking a closer look at this over the coming days,
especially after this system which could paint a clearer picture
once we see how the rivers react.

-Guerrero

&&

.AVIATION (18Z TAFs)...

Flight levels in the Rogue Valley and around Klamath Falls are
fluctuating this morning as fog and ceilings build and dissipate.
Other west side areas are generally at VFR levels under high
ceilings while the east side is lifting to VFR conditions as well.

An approaching cold front will bring widepsread precipitation and
gusty winds later today and into the next TAF period. Low level
wind shear will develop over the Oregon coast and move inland
through the day. Snow levels along and east of the Cascades as
well as the Mount Shasta area and western Siskiyou County of 3500
to 4500 feet will allow for snow showers this afternoon and into
early Thursday morning. Rain showers are expected west of the
Cascades. Both rain and show showers can locally lower ceilings
and visibilities as well as obscure elevated terrain.

-TAD/Hermansen

&&

.MARINE...Updated 200 PM PST Wednesday December 25, 2024...Winds
continue to ramp up as the latest in a seemingly endless parade of
fronts approaches this afternoon. We've already seen gusts over
50 KT in the northern waters, and seas remain extremely steep and
chaotic. Widespread southerly storm force winds are expected by
early evening which will continue into the night, and a storm
warning remains in effect for all waters.

Pressure gradients peak overnight as the front moves through,
after which winds will become more westerly and gradually ease.
There will be a brief break with lower wind speeds tomorrow, but
seas remain extremely high, steep, and hazardous. The next front
brings south gales (at least) back to all areas tomorrow evening,
and to avoid confusion and excessive headlines, the hazardous seas
warning was dropped and replaced by a gale warning from tomorrow
morning through Friday morning. Just understand that even though
winds die down briefly tomorrow, it is not going to be safe out
there. The combination of background swell and fresh swell will
continue to produce large, chaotic seas, especially in the the
surf zone and bars where breaking waves may reach 35 feet.

The parade of fronts looks to continue with one right after
another every day and a half or so right on into the new year.
-Wright

&&

.BEACH HAZARDS...Updated 200 PM PST Wednesday December 25,
2024...Seas will continue to build as the latest in a seemingly
endless parade of fronts approaches this afternoon. This will
result in continued extremely hazardous conditions on local
beaches. Conditions will be particularly dangerous just behind the
fronts as seas become west swell dominated and during the time of
high tide - this occurs both tomorrow morning and behind another
front Friday morning. Breaking waves may reach 35 feet both
mornings. The high surf warning remains in effect through Friday.

During these events, extremely large breaking waves will create
very hazardous and dangerous conditions along beaches and area
shorelines. Waves will inundate beaches and surge into normally
dry areas. Infrastructure damage and significant beach erosion can
be expected. Stay away from area beaches during this period of
active weather.

-Wright

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 10 AM PST Friday for ORZ027-028.

     Wind Advisory from 7 PM this evening to 7 AM PST Thursday for
     ORZ024-026.

     High Wind Warning from 10 PM this evening to 10 AM PST Thursday
     for ORZ021-022-030-031.

     High Surf Warning until 4 PM PST Friday for ORZ021-022.

CA...Winter Weather Advisory until 10 AM PST Friday for CAZ080-082-
     083.

     Wind Advisory from 7 PM this evening to 7 AM PST Thursday for
     CAZ081.

     High Wind Warning from 10 PM this evening to 10 AM PST Thursday
     for CAZ085.

PACIFIC COASTAL WATERS...Storm Warning until 10 AM PST Thursday for
     PZZ350-356-370-376.

     Gale Warning from 10 AM Thursday to 10 AM PST Friday for PZZ350-
     356-370-376.

&&