Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 201128
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
328 AM PST Fri Jan 20 2017

.DISCUSSION...An extensive area of precipitation has pushed into
the forecast area, but the most impacted location is the Mount
Shasta Area, where heavy snow has been falling for several hours.
Although the official observations are showing over half an inch
of liquid precipitation at Mount Shasta City, the snow amounts are
only adding up to a couple of inches. This suggests very wet and
heavy snow, which can be extremely problematic on roads, and on
trees and structures which may not be able to handle the weight. A
Winter Storm Warning remains in effect for that area and the
higher elevations of western Siskiyou County, with Winter Weather
Advisories for other locations where snow is falling, but less
impacts are expected. See the Winter Weather Message PDXWSWMFR for
more details.

The system responsible for producing the snow, wind, and rain
over our area today will open and shift to the north by Saturday
morning, but after only a brief period of high pressure, another
system will quickly replace it on Sunday. Model solutions differ
in the timing and exact placement, but nearly all model suites are
showing a deepening surface low just offshore of the Oregon
coastline, and this pattern could potentially produce a
significant wind event for much of the forecast area. Also, the
orientation of the system would produce upslope flows into the
Mount Shasta region, producing yet another heavy wet snow event.
Currently, High Wind Watches are in place for the coast, the
Shasta Valley, the Rogue Valley, and much of the East Side, and a
Winter Storm Watch is in place for Siskiyou County. A slight
change in the speed or track of the surface low pressure could
make for significant changes to both, and since the models are
still having a tough time finding a consensus, confidence is on
the low side. Also, since current warnings and advisories are in
place, do not want to confuse the message. Therefore, have not
upgraded the watches to their respective warnings, but suspect
that the following shift will do so. Overall, expect wet and windy
weather Sunday into early Monday morning.

Showers will taper off Monday night as the upper level trough
moves to the southeast and ridging builds in aloft. All sign point
to this as the beginning of an extended dry period that should
persist through the remainder of the forecast period. Skies will
therefore be mostly clear, and temperatures should see a gradual
warming trend. However, as is normal for high presure this time of
year, valley inversions will be strong, and fog is likely to form
in the west side valleys overnight and persist into the mornings.
-BPN


&&

.AVIATION...20/12Z TAF Cycle...Rain is spreading across the west
side with light snow on the East Side, including Modoc county,
all of which will create areas of MVFR cigs/vsbys with higher
terrain becoming obscured. Over Siskiyou county in northern
California, widespread IFR cigs/vsbys in snow will improve to
areas of MVFR cigs/vsbys late this afternoon.

&&

.MARINE...Updated 250 AM PST Friday 20 January 2017...South gale
force winds will diminish later this morning. High and very steep
seas will persist over much of the waters this afternoon through
the weekend. Increasing long period west swell will build seas to
a peak of 25 to 30 feet Friday night into Saturday morning.
Another strong storm is likely Saturday night into Sunday with
storm force winds possible. High to very high seas will persist
into early next week. Confidence is low on timing and location of
storm force winds, and that is why the Storm Watch is valid for 30
hours. With that said, most of the latest computer models suggest
a deep enough low in the vicinity of the waters Saturday night
into Sunday to warrant a Storm Watch.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Watch from late Saturday night through Sunday
     afternoon for ORZ029>031.
     Wind Advisory until 1 PM PST this afternoon for ORZ031.
     High Surf Advisory until 10 PM PST this evening for ORZ021-022.
     High Wind Watch from late Saturday night through Sunday
     afternoon for ORZ021-022.
     High Surf Warning from 10 PM this evening to 10 PM PST Saturday
     for ORZ021-022.
     Winter Weather Advisory until 4 PM PST this afternoon for
     ORZ028.
     High Wind Watch from Saturday evening through Sunday afternoon
     for ORZ026.

CA...High Wind Watch from late Saturday night through Sunday
     afternoon for CAZ084-085.
     Winter Storm Warning until 4 PM PST this afternoon for
     CAZ080>083.
     Winter Storm Watch from Saturday afternoon through Sunday
     afternoon for CAZ080-082-083.
     Winter Weather Advisory until 4 PM PST this afternoon for
     CAZ080-081-083.
     High Wind Watch from Saturday evening through Sunday afternoon
     for CAZ081.
     Winter Weather Advisory until 4 PM PST this afternoon for
     CAZ085.

Pacific Coastal Waters...Storm Watch from Saturday afternoon through Sunday evening for
     PZZ350-356-370-376.
     Gale Warning until 7 AM PST this morning for PZZ350-356-370-376.
     Hazardous Seas Warning until 10 PM PST Sunday for PZZ350-356.
     Hazardous Seas Warning from 7 AM this morning to 4 PM PST
     Saturday for PZZ370-376.

$$

BPN/JRS



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