High Wind in Oregon, February 14 to 15, 2021

Area Forecast Discussion
National Weather Service Medford OR
428 PM PST Sun Feb 14 2021

...Updated Aviation Section...

.DISCUSSION...The bulk of the overrunning warm frontal
precipitation has moved out of the region. Southerly winds are
increasing in the coastal waters and on the coast as the cold
front approaches the region, with the warm conveyor flow
precipitation starting to show up on the radar in the coastal
waters. Good dynamics will arrive with better lift and
precipitation will become more significant and spread eastward to
east of the Cascades, overrunning a relatively cold air mass
tonight. Snow levels will bump up significantly from the Cascades
westward, to around 6000 feet overnight. A weak to moderate
Atmospheric River (AR) will deliver mainly beneficial rainfall to
most areas from the Cascades westward below 5000 ft elevation,
especially on the coast and Coast Range, but no widespread
flooding is expected with this AR mainly because the short duration
of heavy rain. East of the Cascades, as is typical, cold air will
linger longer and will provide a chance for moderate snowfall for
elevations generally 4500 feet. A Winter Weather Advisory is in
place for several inches of snow late tonight into early Monday
morning. Many models trend to erode cold air too quickly in warm
frontal situations, but more high resolution models like the HRRR
keeps freezing temperatures through the early morning for much of
the East Side. It's most likely that areas in Lake County and
north and east Modoc County hold on to the cold air and get the
most significant snowfall while areas near Klamath Falls will
likely get a mix of precipitation, and this should limit snow
accumulations there. In short, confidence remains moderate on
snow amounts east of the Cascades, but there is enough potential
for impacting snow to continue the Winter Weather Advisory.
Additionally, expect moderate to occasionally heavy snow this
evening into Monday morning over the high Cascades above 5000 feet
to include Crater Lake and the Diamond Lake area where strong
west flow aloft, perpendicular to the Cascades, will drive high
snowfall rates. A Winter Weather Advisory continues for those
areas. Snow will continue into Monday over the Cascades and snow
levels will lower as colder air moves in. Precipitation should be
lighter though compared to tonight and Monday morning.

A strong wind profile (125kt at 30000ft on this morning's balloon
sounding out of Medford) will eventually translate to gusty winds
over the high terrain and east of the Cascades tonight into Monday.
and a Wind Advisory for much of Lake County and portions of Modoc
county remains in place with 700 mb winds continuing to indicate
in excess of 60 kt.

Showers will mainly affect higher terrain in deep northwesterly flow
Tuesday, with snow levels dropping down to around 2500 feet
Tuesday morning. Wednesday will bring a break in the action as
and upper level ridge of high pressure noses into the forecast
area. Runoff from recent rainfall will result in river levels
increasing, but recent models for the Coquille River at Coquille
are keeping levels below action stage into next week at this time.
Please stay tuned to river forecasts if you live in flood prone
areas.

.Extended Discussion...(Thursday through Sunday) Overall the
extended period of the forecast has not changed. We'll remain in a
progressive pattern with a series of storms moving through the
area. Any breaks in the action are expected to be short in
duration (12 hours or less). The next storm will push into the
forecast area early Thursday morning with over running
precipitation as a warm front pushes into the area. Snow levels,
at least west of the Cascades will have a chance to rise to 6000
to 6500 feet and around 3500-4000 feet east of the Cascades
Thursday. Favorable moist upslope flow from the southwest will
result in moderate to heavy precipitation for the coast, coastal
mountains in southwest Oregon and Cascades. There's still some
indication for an AR (atmospheric river event) Thursday into
Thursday evening before an upper trough pushes the heaviest
precipitation south into northern California Thursday night. The
signal is not as strong as yesterday, but it remains in line with
several individual ECMWF ensemble members and the peak of IVT
(integrated water vapor transport) depicted by the ECMWF and GEFS
ensembles. Gusty winds are also possible at the coast and
headlands Thursday.

Thursday evening, the upper trough moves into the area with the main
focus for precipitation shifting into northern California and it
will be at this time snow levels will begin to lower to the higher
passes along the Cascades, eastside and possibly Siksyou Summit.
However precipitation will be diminishing, thus limiting the amount
of snow accumulation.

A relative break in the action is possible Friday. The operational
ECMWF shows another stronger shortwave moving in from the northwest
with precipitation increasing in southwest Oregon and northwest
California, However the individual ECMWF ensemble members is not as
clear and the GFS shows brief ridging. Given it's coming in from
the northwest, they tend to move in quicker than what the
operational models give credit for, therefore confidence is low on
low long, if any break we'll get. The next system will bring
increasing winds to the coast followed by increasing precipitation
starting Friday afternoon or evening and lasting through Friday
night.

Active weather continues next weekend with fast and a moist
northwest flow with additional systems moving through. Systems that
move through will be quick movers with the best chance for
precipitation along and west of the Cascades. -Petrucelli

&&

.AVIATION...For the 15/00Z TAF Cycle...From the Cascades
west...VFR is occurring in many places, however partial mountain
obscurations are still possible into this evening. Ceilings will
lower to MVFR with brief IFR possible in heavier precipitation later
this evening into Monday morning. Low level wind shear will be an
issue at North Bend, Roseburg and Medford this evening. East of the
Cascades...MVFR and brief IFR ceilings and visibility will be a
concern at Klamath Falls this morning. Precipitation should end with
ceilings improving to VFR this afternoon, but it's possible the
lower conditions could go for an hour or two longer than whats in
the Klamath Falls TAF. Also expect partial obscuration over the
higher terrain. Ceilings and visibility will come down again this
evening with MVFR and occasional IFR conditions possible, especially
during times of heavier precipitation. Low level wind shear is also
a concern for Klamath Falls tonight into Monday morning, before
stronger winds begin to surface Monday morning. -Schaaf/Petrucelli

&&

.MARINE...Updated 200 PM PST Sunday 14 Feb 2021...Strong south winds
will continue this afternoon reaching gale force at times near Buoy
15.  These strong south winds will continue through this evening
into tonight over the inner waters when a cold front swings through
the region. Once the front moves through, look for westerly winds
around 15 to 20 knots over the waters. In addition to the winds, the
seas will remain high and steep tonight through early Monday
morning. These seas will come close to 18 feet in the outer waters
on Monday, which is considered hazardous seas. For now, we'll
continue to advertise the seas as high, steep and hazardous to
smaller crafts.

Another weak cold front will move through the waters around Monday
night keeping the winds and seas hazardous to smaller crafts.
Wednesday will be a bit of reprieve as high pressure builds, which
allows for seas to fall below 10 feet. Winds and seas will then be
on the rise again Thursday when a strong warm front pushes into the
Pacific Northwest. Smith

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Small Craft Advisory until 10 AM PST Wednesday for ORZ021-022.
     Winter Weather Advisory from 7 PM this evening to 10 AM PST
     Monday for ORZ030-031.
     Wind Advisory from 1 AM to 10 PM PST Monday for ORZ030-031.
     Winter Weather Advisory until 1 PM PST Monday for ORZ027-028.
     Winter Weather Advisory from 7 PM this evening to 10 AM PST
     Monday for ORZ029.

CA...Wind Advisory from 1 AM to 10 PM PST Monday for CAZ085.
     Winter Weather Advisory from 7 PM this evening to 10 AM PST
     Monday for CAZ085.

Pacific Coastal Waters...Small Craft Advisory until 10 AM PST Wednesday for
     PZZ350-356-370-376.

SBN/SBN/SBN