High Wind in Oregon, January 12 to 13, 2021

Area Forecast Discussion
National Weather Service Medford OR
803 PM PST Mon Jan 11 2021

.Updates...Updates to PoPs.

.DISCUSSION...Rain has been ongoing at the coast for a few hours
now with the onset of this atmospheric river. Already a few
stations in Coos and Curry county have reported a quarter inch of
rain. Other stations, especially at lower elevations, have
reported a tenth of an inch. Inland, rain is also beginning to
accumulate. In Douglas and Josephine County some higher elevation
stations are reporting a few hundreths. Have increased pops in
Douglas and Josephine county to account for this.

Winds are also beginning to come up. Offshore buoy 15 has
reported a maximum gust of 40 mph, while in the headlands the
strongest gust so far has been 30 mph. Winds are beginning to be
felt along the higher terrain further inland, but will take three
to five more hours before they begin to be felt in the valleys.

The forecast otherwise remains on track. The forecast discussion
below has expanded details on the forecast. -Miles

&&

.AVIATION...For the 12/00Z TAFs...Lingering areas of IFR cigs are
finally eroding and once this clears, VFR conditions will prevail
across the area into the evening. A strong front is pushing into the
region this afternoon and there is plenty of high level cloud cover
associated with it. Cigs will gradually lower to MVFR first at the
coast, then moving onshore and spreading inland to the Cascades
tonight with higher terrain becoming obscured. Areas east of the
Cascades will remain VFR, but some higher terrain will become
obscured. 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 this evening and overnight. /BR-y

&&

.MARINE...Updated 745 PM PST Monday, 11 Jan 2021...South winds will
increase to gales this evening as a strong and very wet frontal
system approaches. Southerly wind seas and long period westerly
swell will build tonight through Tuesday with combined seas expected
to reach 20 to 25 feet across the area during the day on Tuesday.
Winds may increase to storm force from Cape Blanco northward to
Florence between 3NM and 25NM of the coast from about sunrise to
early afternoon. Seas will then gradually subside Wednesday into
Thursday.

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 feet at 17
seconds. ~BTL/BR-y

&&

.BEACH HAZARDS...Updated 800 PM PST Monday, 11 Jan 2021...Another
long period swell will arrive Tuesday morning, resulting in another
period of hazardous surf conditions with breaking wave heights of 27
to 32 ft. In addition, these large breaking waves will coincide with
a king tide Tuesday morning, increasing the risk of flooding for low
lying areas along the coast. The risk for flooding will diminish
late Tuesday into Wednesday as tides lower and dangerous surf
conditions will improve Wednesday morning 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!

&&

.PREV DISCUSSION... /Issued 354 PM PST Mon Jan 11 2021/

Updated Aviation and Marine Discussions...

SHORT TERM...Satellite is showing the low clouds hanging on in
some of the valleys this afternoon, but areas east of Klamath
Falls and in NE California have some sunshine. Even if some of
those valleys lose the low clouds this afternoon, more clouds are
streaming in from the Pacific in advance of a long duration
atmospheric river expected to commence across SW Oregon/far NW
California tonight. Radar is showing some echoes moving in from
the Pacific and it may begin raining before sundown in some
coastal locations. After that, expect periods of moderate to heavy
rain at the coast tonight into early Wednesday morning as moisture
transport increases aided by strong 850-700mb flow within the AR.
We have areal flood watches out for the coast zones with expected
rainfall of 2-3 inches north of Cape Blanco and 4-8 inches in
Curry County (highest totals in the coast ranges due to orographic
enhancement). The areal flood watch has also been expanded to
include zone 24 (eastern Curry/Josephine County), but flood
potential is less likely in the northeast portion of the zone near
Grants Pass. Rain spreads inland tonight, but due to the strong
mid-level west-southwest flow, there will be some downslope into
the west side valleys. This flow rises up into the Cascades, so
there should be another area of more enhanced precipitation north
of Highway 140 in the mountains. Overall, rain amounts inland will
be 1-3 inches, a little less here in the Rogue Valley and a
little more in the Cascades. This should be largely beneficial in
those areas though with some absorption by the snow pack in the
Cascades/Siskiyous. Even so, with some melting of the snow due to
a surge in snow level to 7000-9000 feet, expect some added inflows
into the drainages. While significant rises are expected on most
basins from the Cascades westward, most main stem rivers (at least
at this time) are expected to peak below flood stage. Little
change was made to the QPF forecast today, but it should be noted
that the crest of the Coquille River at Coquille dropped a little
since last night and it now peaks near action stage. This is
mainly due to the river being about a foot lower than the previous
forecast rather than a decrease in QPF. Nonetheless, the river
flood watch continues. East of the Cascades, rainfall will
diminish greatly such that portions of eastern Lake County and
Modoc County will largely miss out on this event.

There will also be an extended period of strong winds along the
coast and over the east side where high wind warnings are in
effect. Strong KOTH-KACV gradients of -8 to -10mb continue to
support wind gusts of 60-70 mph at the coast with up to 80 mph at
the headlands. The 700 mb winds east of the Cascades during the
warnings peak at 65-70kt, so gusts of 65 mph should also occur
along Highway 31 near Summer Lake. -8 to -10 mb KMFR-KRDD
pressure gradient also supports advisory level winds in the
Shasta Valley. This typically might also indicate the potential
for warning level winds, but with more of a southwest or westerly
component to the mid-level flow, wind speeds should be lower than
if they were truly valley-aligned. See the wind headlines at
NPWMFR. Breezy conditions are expected elsewhere at times and
especially at the southern portion of Rogue Valley.

Winter impacts will be minimal with this event. As the cold front
moves onshore Wednesday, the AR shifts southward and snow levels
will drop to around 5000 feet, but precipitation should be ending
during that time and snow amounts would be light. -Spilde

LONG TERM...Thu 14 Jan through Mon 18 Jan 2021.

The extended period will begin with a strong ridge along the west
coast. The ridge axis will break to the east of the area Thursday
night. Flow aloft will become zonal. The upstream trough will weaken
as it approaches the coast, and what is left of it will move onshore
Friday. The associated front will move onshore Thursday night into
Friday. The EC and the GFS have converged on this feature, both now
forecast a weak front and thus a low impact event. Snow levels will
drop quite a bit behind the front, down to 4000-5000 feet. Any post-
frontal showers will end Friday night.

Another ridge will build off the coast Saturday, weaken slightly
Saturday night into Sunday, then rebuild Sunday into Monday.
Saturday through Monday looks to be dry and cool. -JRS

&&

.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 from 1 AM Tuesday to 6 AM PST Wednesday for
     ORZ021-022.
     High Wind Warning from 1 AM Tuesday to 4 PM PST Wednesday for
     ORZ030-031.

CA...Wind Advisory from 1 AM Tuesday to 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 Watch from 7 AM PST Tuesday through Tuesday afternoon for
     PZZ350-370.