High Surf in Oregon, January 12 to 13, 2021

Area Forecast Discussion
National Weather Service Medford OR
355 AM PST Tue Jan 12 2021

Updated Aviation Discussion.

.DISCUSSION...

Forecast remains on track as some strong winds are expected to
hit the coast later today. The latest forecast is showing 925 mb
winds around 60 to 65 knots as a strong pressure gradient develops
over the area. The headlands and the coast are the areas of
greatest concern. Cape Blanco may see gusts up to 75 mph later
this morning when the strongest winds develop along the coast.

The story remains the same for other areas farther inland and
east of the Cascades. 700 mb winds are forecast to be around 40 to
70 knots peaking around Tuesday night into Wednesday morning.
Usually winds this strong out of the west produce issues along
highway 31 near Summer Lake. This event is by no means historic,
but could cause some issues for high profile vehicles traveling
that route Tuesday night.

As for many of the valleys west of the Cascades, the winds
definitely do align with the Shasta valley. Therefore, Weed CA
will likely see wind gusts around 45 mph later today. The Rogue
Valley is a little more uncertain as the low level winds don't
align with the valley. Ashland will probably remain windy for the
day with sustained winds around 15 to 20 mph and gusts
approaching 45 mph. We stayed away from a wind advisory here
because the winds are not south east enough higher in the
atmosphere. With that being said, the SREF is predicting winds
around 10 mph in Medford, a critical threshold for some
meteorologists in the office to issue a wind advisory.

Aside from the lengthy discussion about winds, rain will remain an
impact for areas west of the Cascades, especially along the coast.
The latest analysis classifies this atmospheric river(AR) event
as a beneficial AR. The exception might be around Curry County,
where we're forecasting 6 inches over the coastal range. The
Brookings area will be under the heaviest rain until roughly 12z
Wednesday. This area historically sees a lot of rain anyways, and
6 inches shouldn't cause major issues. To be safe, we did keep
areal flood watch for most of the coast and eastern Josephine
County.

We're also expecting the Coquille River at Coquille to approach
the minor flood stage. The latest forecast has the river cresting
at 20.7 feet with the minor flood stage at 21.0 feet. Small errors
in the QPF forecast could easily push this river into flood.

After Wednesday afternoon, the cold front passes through and dry
air filters in with high pressure building rapidly over Oregon.
Given the ample surface moisture from all the rain and clearing
skies, dense fog seems likely in many of the valleys east and west
of Cascades.

Models are predicting some weather moving in around Friday
afternoon and evening. This event looks much drier and less
dynamic compared to what we'll see today through Wednesday
morning. Overall, ensemble data suggests nothing major coming
Friday into early next week. It looks like a strong area of high
pressure will build over the Pacific around Tuesday and Wednesday
with anomalously warm temperatures along the coast.

-Smith

&&

.AVIATION...For the 12/12Z TAFs...A strong front is pushing into the
region and there is plenty of high level cloud cover associated with
it.  MVFR cigs/vis at the coast will gradually spread inland across
areas from the Cascades west this morning, then conditions will
become  MVFR cigs/vis with areas of IFR this evening and tonight.
East of the Cascades, expect mainly VFR this morning with some
higher terrain obscured, then becoming areas of MVFR cigs late this
morning, continuing through tonight. In addition, strong winds aloft
with this front leads to low level wind shear concerns for areas
west of the Cascades, including KOTH, KRBG, and KMFR today into
tonight. LLWS will be a concern east of the Cascades as well,
including KLMT, until these stronger winds surface later this
morning and this afternoon. -CC

&&

.MARINE...Updated 200 AM PST Tuesday, 12 Jan 2021...A very strong
and very wet frontal system is bringing gale force winds and very
steep seas to the waters today. Winds will increase this morning
into this afternoon with winds across portions of the waters from
Cape Blanco northward reaching storm force. The strongest winds are
expected between 2 nm and 25 nm of shore from Cape Blanco to
Florence. Gales will then continue across all the waters this
evening, gradually lowering from north to south over the waters
tonight into early Wednesday morning. Very high and very steep
combined seas of 20 to 25 ft are expected today and tonight due to a
mix of very steep wind seas and large, long period swell. Steep
seas, dominated by west swell, are expected on Wednesday.

High pressure will bring a break in the action Wednesday afternoon
through Thursday night. A weaker frontal system is then expected to
move through Thursday night into Friday before high pressure and
northerly winds build in for a few days. Another long period heavy
west swell event is likely Friday night, peaking at 17 to 18 feet at
17 to 18 seconds. -CC

&&

.BEACH HAZARDS...Updated 200 AM PST Tuesday, 12 Jan 2021...Another
long period swell will arrive today, resulting in another period of
hazardous surf conditions with breaking wave heights of 27 to 33 ft.
In addition, these large breaking waves will coincide with a king
tide this morning, increasing the risk of flooding for low lying
areas along the coast. The risk for flooding will gradually lower
late tonight into Wednesday as tides lower and dangerous surf
conditions improve as seas begin to lower.

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!

CC

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning until 10 AM PST Wednesday for ORZ021-022.
     Flood Watch through Wednesday morning for ORZ021-022-024.
     High Surf Warning until 6 AM PST Wednesday for ORZ021-022.
     High Wind Warning until 4 PM PST Wednesday for ORZ030-031.

CA...Wind Advisory until 10 AM PST Wednesday for CAZ081.

Pacific Coastal Waters...Flood Watch through Wednesday morning for PZZ350-356.
     Gale Warning until 4 AM PST Wednesday for PZZ350-356-370-376.
     Storm Warning until 4 PM PST this afternoon for PZZ350-370.