High Surf in Oregon, January 11, 2020

Area Forecast Discussion
National Weather Service Medford OR
348 AM PST Sat Jan 11 2020

.SHORT TERM...
Forecast remains on track this morning with heavy snow showers
over the Cascades with snow levels right around 3500 feet. The
most intense snow fall will continue this morning as this low
moves through the Pacific Northwest. We expect the rain and snow
to taper off in intensity this afternoon and early evening as some
drier air is able to settle over the area briefly. You can
actually see the drier air on the satellite water vapor imagery
right now. Other than the snow, winds will be rather brisk later
this afternoon. We're expecting strong winds east of the Cascades
with gusts up to 50 mph near Silver Lake and around highway 31.
With the strong winds, drifting snow may result in periods of
significantly reduced visibility.

Then, the next system will hit the forecast area late this
evening through Sunday. Again, the northern Cascades will be
under the gun as strong westerly flow slams up against the
western facing slopes. 850 mb winds are around 40 knots around the
Diamond Lake area, which will result in some impressive
orographic forcing and precipitation. Eventually, a cold front
will push onshore with this system on Sunday. Snow levels will
start out around 3500 feet before falling evening further down to
3000 to 2500 feet later in the afternoon and evening. This will
result in the foothills seeing accumulating snow during the tail
end of Sunday.

Snow levels will then finally take another dip down to 1500 feet
Sunday night. We'll see accumulating snow over the lower I-5
passes and down to the valleys. The key point here is that the
precipitation will be more showery, so it's not going to be an
intense blanked of continuous snow. The snow will probably be
between a trace to an inch in the valleys and over the lower I-5
passes Sunday night.

The next system will arrive later on Monday evening. Snow levels
will rise to around 2500 feet Monday evening when the bulk of rain
and snow arrives. Since the flow is more southerly, Siskiyou
Summit and the Mt Shasta area are the main areas of concern Monday
since they handle more transportation then the high Cascades.
Since the low level flow isn't that intense, we're not expecting
extreme impacts along the I-5 corridor in Siskiyou County.

-Smith

.LONG TERM.../Issued 253 PM PST Fri Jan 10 2020/
Tuesday through Friday...The bottom line: expect copious amounts
of snow if you are higher than 4000 feet and expect at least some
snow (except for the coast) if you're below 4000 feet.

We are confident that the extended forecast will remain quite
active. We are also confident that many of the storms next week will
provide some relatively significant snows, especially for the
mountains and the passes over the next week. We have low confidence
regarding the timing of the systems and what the exact snow levels
will be. That being said, we do expect snow levels to reach valley
floors on Tuesday evening and Tuesday night. Have gone with a blend
of the US National Blend of Models (NBM), the previous forecast, and
a few other models as well to help make a guess with the timing of
the systems since the NBM is ensemble based and by design will
spread out precipitation chances.

The first of the systems will have moved through our area by
Tuesday, leaving lingering showers. Snow levels are expected to be
just above the valley floors during the day (around 1400 feet or
so), but once the sun sets, the snow levels will fall once again
likely reaching the valley floors. The snow levels could fall enough
to reach Roseburg. Valley Floor snow amounts will not be very high
(less than an inch), but the passes including Jacksonville Hill,
Hayes Hill, Camas Mountain could see a few inches.

The next storm arrives on Wednesday and will provide another blast
of precipitation across southern Oregon and northern California.
Snow levels will rise to around 1500 to 2000 feet throughout the
day, and they are expected to hover around there for the rest of the
week. The main issue here will be whether or not any shortwaves
during this system could bring potentially heavy enough
precipitation to bring down snow levels another 500 to 1000 feet in
small areas.

After a brief break with lingering showers Wednesday night, the next
system will come through on Thursday and could be even stronger than
the first system. Similar snow levels and amounts are expected
during this period. Another system is poised to reach the area next
weekend as well.

In all we're expecting 2-4 feet of snow in the Cascades in the
extended forecast, with 1-2 feet over the next week at Siskiyou
Summit and some of the lower passes 2-3 feet around Mt. Shasta City,
and up to a foot of snow across the east side. Reminder, although
these amounts are high, each system will bring only a portion of
these numbers with the biggest system coming in Thursday. Please
stay tuned to the weather forecast as there will be many snow
impacts for a lot of people, and since confidence is low; expect
changes to the extended forecast.

-Schaaf

&&

.AVIATION...For the 11/12Z TAF Cycle....Showers will continue to
produce areas of MVFR cigs/vsbys and local IFR cigs/vsbys in low
clouds and rain/snow along with obscuration of higher terrain. Snow
levels will be around 3,000-2,500 feet Saturday. Low level wind
shear will also be a concern at KRBG and KLMT for mostly speed shear
into early morning. The MVFR/IFR conditions with precipitation and
gusty winds will persist for most, if not all, of the forecast area
into Saturday afternoon. A brief pause in poor conditions may occur
saturday evening, but will again deteriorate as another front pushes
onshore overnight.

-miles

&&

.MARINE...Updated 130 AM PST Saturday 11 Jan 2020...A strong front
has moved inland. Very high and very steep northwest swell will
build to a peak of around 22 to 27 feet at 16 seconds today. Winds
and seas will then diminish, although seas will remain very high and
very steep through Sunday morning.

The series of fronts will continue Sunday through Tuesday with
periods of advisory strength winds while seas remain high and steep
to very steep.

A significantly strong front is possible at mid-week which may bring
another episode of gales and very high seas Wednesday into Friday.

-miles

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 10 PM PST Sunday for ORZ029-030.
     Winter Storm Warning until 10 PM PST Sunday for ORZ027-028-030.
     Winter Weather Advisory until 10 PM PST Sunday for ORZ031.
     Wind Advisory from 7 AM this morning to 4 PM PST this afternoon
     for ORZ031.
     High Surf Warning until 10 PM PST this evening for ORZ021-022.
     Winter Storm Warning until 10 PM PST Sunday above 3000 feet in
     the for ORZ025-026.

CA...Winter Weather Advisory until 10 PM PST Sunday for CAZ085.
     Winter Weather Advisory until 10 PM PST Sunday above 3500 feet
     in the for CAZ080.

Pacific Coastal Waters...Hazardous Seas Warning until 2 AM PST Sunday for
     PZZ350-356-370-376.