High Surf in Oregon, January 10, 2021

Area Forecast Discussion
National Weather Service Medford OR
357 AM PST Sun Jan 10 2021

.DISCUSSION...Radar imagery shows a band of precipitation moving
from west to east across southern Oregon and northern California.
This band is attached to a frontal boundary that is moving across
the area. This front will likely stall over the Cascades or just
east of the Cascades and dissipate this morning. Behind the
front, a few showers are expected, before things dry out. With the
clouds ahead of the front, do not anticipate that many sheltered
locations saw cold air pooling with freezing rain (below snow
levels of 5000 feet). I do not expect significant impacts with
this system, but roads may be slick in a couple of isolated spots.

Overall, after 10 AM, expect a dry day with some lingering clouds.
The inversion will come back tonight with fog, freezing fog, and
low clouds setting up across almost all valleys in our forecast
area Sunday night into Monday morning. This will be relatively
short lived as the next front moves through Monday morning. Models
remain in agreement that this front will slow down, keeping most
precipitation chances west of the Cascades. The reason this front
will slow down is that the flow is becoming more southwesterly
in response to a deepening low/upper trough offshore. This will
allow that front to lift back to the north as a warm front. A more
significant push of moisture into the area Monday night is
accompanied by a surge in snow levels to above 7000 feet, but most
areas south and east of the Cascades will remain dry during this
timeframe.

This extra surge of moisture has been hinted at for about a week
and a half now, yet there are details that remain hazy in regards
to how exactly it will play out. Models have strengthened the
front, and the strongest part of the front (and heaviest
precipitation) will occur well to the north of our forecast area.
Still, the front looks to be stretched as the northern half of the
front pushes eastward while the southern periphery in our area
stalls over the Cascades again. At that point, an atmospheric
river looks to move into our area Tuesday night into Wednesday
before lifting northward out of the area on Thursday. This
atmospheric river shows quite extensive moisture transport, and
the three-day nature of this system indicates that we could be
seeing a 1 in 5 to 10 year sort of event (between the weaker GEFS
and the stronger EC Ensemble).

Have increased rainfall amounts across the coast range,
specifically in Curry County where the southwest flow is the
deepest. Yet the entire coast range and portions of the Cascades
will see periods of moderate to heavy precipitation. Snow levels
hover between 7000 and 9000 feet, so wintry impacts will be
minimal; however, the good news is that we have generated enough
snow pack that most of the rain will be absorbed into the snow
(like a sponge) with only some of the snow pack running off.
Still, with previous events, we've seen reports of isolated rock
falls over highways heading toward the coast, and this could be
possible once again. Have coordinated with the Weather Prediction
Center and think that a marginal risk (5%) for flash flooding
during this time period is warranted along and west of the Coast
range. Meanwhile, most of the precipitation will be along and west
of the Cascades with areas east of the Cascades missing out on
a majority of any moderate or heavy precipitation.

A ridge of high pressure builds back in over our area on Thursday
with additional fog and stratus setting up with the inversion on
Wednesday night. Then, another front will move through our area
Thursday night into Friday. This front will be weak, and should
dissipate relatively quickly. Precipitation looks to remain light
and be focused once again along and west of the Cascades and
largely north of the Umpqua Divide. Once again, however, snow
levels will remain high (around 6000-7000 feet).

High pressure quickly builds back in for the weekend with largely
benign weather for Martin Luther King Jr. day. -Schaaf

&&

.AVIATION...For the 10/12Z TAFs...A front is moving across the
region and will reach the Cascades a little before sunrise. mostly
MVFR with higher terrain obscurations and isolated IFR conditions
will continue as this front moves east of the Cascades later this
morning. MVFR conditions will move in east of the Cascades as the
front moves east, with areas of higher terrain obscured. However,
all areas will clear to VFR by this afternoon. most valleys across
the region should see MVFR with some valleys seeing IFR condition
developing by tomorrow morning. Sven

&&

.MARINE...Updated 330 AM PST Sunday 10 Jan 2021...Winds have
eased behind the front with another high and long period swell
moving in behind the front, peaking at around 20 to 23 ft this
morning and afternoon.

Swell gradually lowers late today into Monday, but another front
and long period swell are expected late Monday into Tuesday. South
winds will increase again ahead this next front around Monday
afternoon through Monday night and there is the potential for gales
Monday night. Active weather will continue through the week, with
additional heavy and long period swell trains expected Tuesday and
again towards the end of the week. /BR-y/Sven

&&

.BEACH HAZARDS...Updated 800 PM PST Saturday 09 Jan 2021...After a
brief period of improved surf conditions this afternoon, another
very high and long period swell moves into the area late tonight
into Sunday morning. This next swell group arriving tonight is
expected to be 4 to 5 feet higher compared to what moved into the
coast yesterday. Large breaking waves of 25 to 30 feet are possible
with this event and a High Surf Warning is in place to cover this.
In addition, the swell will be moving in during some higher than
usual high tides. Therefore, there is a concern of some coastal
flooding near Harbor, OR and a small section of highway 101 south of
Coos Bay. While these are the only known locations along the
southern Oregon coast that are prone to flooding during these very
high tides and large swell events, the potential is there for other
low lying areas to flood as well. So use extra caution when out and
about tonight into Sunday.

Use extreme caution along and near the beaches and stay away from
the ocean. Jetties, rocks, logs and bar entrances are not safe
places to be during this period of significant waves. The Pacific
Ocean is both cold and powerful. These large waves can easily sweep
people and large objects into the water. NEVER turn your back on the
ocean!

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Surf Warning until 10 PM PST this evening for ORZ021-022.

CA...None.

Pacific Coastal Waters...Gale Watch from Monday evening through Tuesday afternoon for
     PZZ350-356-370-376.
     Small Craft Advisory from 10 PM this evening to 7 PM PST Monday
     for PZZ350-356-370-376.
     Hazardous Seas Warning until 10 PM PST this evening for
     PZZ350-356-370-376.