Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 161151
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
351 AM PST Tue Jan 16 2018

Updated AVIATION Section

.DISCUSSION...

Precipitation is ongoing this morning as this cold front pushes
through the region. Snow levels are roughly around 5000 feet as
the Mt. Ashland lodge cameras at 6000 feet were showing snow
earlier this morning.

The rest of the focus remains on the upcoming system on Thursday.
Models are in ok agreement with the NAM being an outlier,
especially with the QPF on Thursday. Winds are in general more
southerly in the NAM compared to the other solutions leading to
some pretty drastic downsloping effects for the west side valleys.
The SREF actually has more precipitation for Medford than the NAM
during Wednesday night, which is fairly unusual to say the least.

Anyways, the forecast calls for 3.0 inches of rain near Brookings
from 0z Thursday until 12z Friday and about a half inch in the
west side valleys. For the Cascades, we`re forecasting about 1
inch of liquid, which should come down as rain first with snow
levels around 7000 feet. Then the snow levels will drop rapidly
with the frontal passage down to 3500 feet Thursday evening. Snow
accumulations are looking ok with 10 inches expected for Crater
Lake and Mt Ashland between 0z Thursday and 12z Friday. The low
that will be impacting the region will continue to bring some
showers to the region Friday and Saturday. So those snowfall and
rainfall totals will continue to increase as time moseys on.
Right now the forecast is calling for 17 inches of snow at Crater
Lake and Mt Ashland from 0z Thursday through 12z Sunday. That is
probably on the high side given that its dependent on showers
precipitating precisely on those locations.

The last topic is winds as this strong low in the gulf of Alaska
will create some strong pressure gradients between Redding and
Medford during 6z Thursday. We`re looking at the gradient around
7-8 mb, which is usually a good indicator of strong winds in the
Shasta valley. As for the east side, it`s a bit tougher to say as
the 700mb winds drop down to 55 knots as they head east. Would
like to see those winds stay stronger in the 60 -70 knot range for
a high wind warning near Summer Lake, so we kept the high wind
watch going for tonight. It should be noted the Rogue valley will
also be a little windy, but the flow doesn`t align perfectly with
the valley, so no wind products expected there.

-Smith

&&

.AVIATION...16/12Z TAF CYCLE...Local IFR fog/low stratus is
expected in the valleys west of the Cascades this morning. LIFR is
showing up at the Grants Pass airport at 12z and probably will
impact some terminals in the Umpqua, Rogue and Illinois Valleys as
well this morning. These lower conditions should gradually lift to
VFR for all areas this afternoon. Overall, tonight will be VFR,
except local IFR again in fog/low stratus in the valleys west of the
Cascades toward morning. Stronger winds aloft will reach the coast
by Wednesday morning, so low-level wind shear is possible at North
Bend after 10z. -Spilde

&&

.MARINE...Updated 230 AM PST Tuesday 16 Jan 2018...Conditions will
be hazardous to small craft today through tonight with a westerly
swell of 12-15 feet at around 14 seconds. A strong Pacific front
will move into the waters Wednesday and winds will increase to gale
force Wednesday morning with storm force winds possible in the
waters beyond about 15 NM from shore and north of Cape Blanco. The
front will move onshore Wednesday evening and winds will subside
overnight. Gale/storm watches have been upgraded to warnings.

Model guidance is in agreement that a very high west swell will
arrive Wednesday night. The models are indicating swells as high as
30 feet, which would be historically high. Confidence in this
occurring is high, so we have opted to hoist a High Surf Warning
along the coast with longer than usual lead time, in order for
coastal ports/harbors to prepare. This can be viewed at CFWMFR. It
goes without saying that bar conditions will be downright dangerous
with extremely rough surf. Mariners are urged to use extreme caution
or just remain in port until this period of stormy weather ends.

Weaker storms will follow Thursday into Friday. Another strong front
will move onshore sometime next weekend. -Spilde


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Surf Warning from 4 PM Wednesday to 7 AM PST Saturday for
     ORZ021-022.
     High Wind Watch from Wednesday afternoon through late Wednesday
     night for ORZ030-031.

CA...High Wind Watch from Wednesday morning through Wednesday evening
     for CAZ081.

Pacific Coastal Waters...Small Craft Advisory until 7 AM PST Wednesday
     for PZZ350-356-370-376.
     Gale Warning from 7 AM to 7 PM PST Wednesday for
     PZZ350-356-370-376.
     Hazardous Seas Warning from 7 PM Wednesday to 4 PM PST Saturday
     for PZZ350-356-370-376.
     Storm Warning from 7 AM to 7 PM PST Wednesday for PZZ370.

$$

CZS/MAS/MAS



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