Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 191603
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
803 AM PST Sun Feb 19 2017

.DISCUSSION...Rain and snow are affecting the forecast area this
morning as another front moves through from west to east. Snow
levels, per observations, are about 3000 feet this morning so the
forecast looks on track. Winter Weather Advisories continue for
the mountains of Siskiyou County as well as the Siskiyous and
Cascades in Oregon, generally about 3000 feet. Precipitation
will diminish this afternoon and road temperatures will warm, so
may be able to end these Advisories early than the 1pm scheduled
ending time.

A very active weather pattern continues through Tuesday at least.
We`ll be examining the expected impacts of the northern edges of
an Atmospheric River impacting the area, bringing moderate to
heavy precipitation, and two surface lows approaching the coast
that will bring windy conditions to much of the forecast area.
Exactly how windy is a question we`ll be attempting to answer
today. Please see the previous discussion below for details on the
active weather pattern and the cooling trend/lowering snow levels
after Tuesday.

&&

.AVIATION...19/12Z TAF CYCLE...Areas of MVFR/IFR cigs with higher
terrain obscured will persist through this morning with widespread
showers, breezy south winds, and freezing levels of around 3000 to
4000 feet above sea level. Late this morning and into the
afternoon, expect conditions to improve somewhat mostly VFR with
areas of MVFR, and showers gradually decreasing in coverage and
intensity. -BPN/Sven

&&

.MARINE...Updated 400 AM PST Sunday 19 February 2017...South winds
will slowly decrease through the day and into tonight. High long
period swell will build over the waters late today. Two storms could
impact the waters Sunday night through Monday night with the
potential for gales and very steep seas before conditions improve
toward midweek. Sven

&&

.PREV DISCUSSION... /Issued 350 AM PST Sun Feb 19 2017/

DISCUSSION...Deep low pressure over the northeast Pacific will
continue to usher in wet and windy weather at times to the region
through Tuesday. Thereafter through late week the weather will
turn colder as the trough migrates across the Pacific Northwest
and a cold northerly flow sets up.

The trough passing through this morning is accompanied by
unstable conditions over the coastal waters north of Cape Blanco
where several lightning strikes are being observed in cell
clusters moving onshore around Florence. Conditions will remain
similar there through the day with the instability moving off to
the north by evening. Meanwhile, moist onshore flow and ample
dynamics will provide widespread moderate shower activity inland
across the west side and Cascades. A winter weather advisory
continues through the morning with snow levels between 3000-3500
feet. 2 to 5 inches of additional accumulation looks likely today
across the Cascades and Siskiyous but precipitation rates will
taper off by afternoon as snow level rise in flow transitioning to
southerly.

The GFS and ECMWF are somewhat similar in advertising a deep
surface low to move from south to north through the coastal waters
late tonight through Monday morning. A gale warning has been
issued for this event. In addition, high wind watches have been
issued for the Shasta Valley and Summer Lake areas as southwest
flow between 700-500 millibars increases to 60 to 85 kts.
Increasing precipitation rates will occur with heavy rain mainly
on tap for the coast through Josephine county and Siskiyou
county.

Yet another short wave will roll through Monday night into early
Tuesday with a period of heavy rain and mountain snows. Will need
to watch the surface low forecast as the GFS is indicating another
fairly strong surface low to move up the coastal waters with a
potential high wind event. Not seeing a lot of agreement in the
operational solutions or ensembles so confidence is marginal at
this time. Despite the wind uncertainties, confidence on
precipitation amounts is pretty good.

The Scott River at Fort Jones and the Klamath River at Seiad
Valley are forecast to get close to flood stage by Tuesday morning.
A hydrologic Outlook is in effect for these areas and flood
watches may be required later this morning or this afternoon after
coordination with the River Forecast Center in Sacramento. Storm
total precipitation amounts from Curry through southern Josephine
and Siskiyou Counties will range from 2 to 6 inches from this
morning through Tuesday.

The pattern transitions to a cool and showery regime later in the
week with snow levels dipping to valley floors across the west
side Thursday through the weekend. Some low elevation snow
accumulations look possible, but details are fairly uncertain at
this time. Have knocked down some of the temperature forecasts in
this time frame several degrees.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 10 PM PST Monday for ORZ030-031.
     High Wind Watch from this evening through Monday morning for
     ORZ030-031.
     Winter Weather Advisory until 1 PM PST this afternoon ABOVE 3000
     FEET for for ORZ025>028.

CA...Winter Weather Advisory until 1 PM PST this afternoon for
     CAZ082-083.
     Winter Weather Advisory until 1 PM PST this afternoon for
     CAZ080.
     Wind Advisory until 4 PM PST Monday for CAZ081.
     High Wind Watch from this evening through Monday morning for
     CAZ081.

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

$$

NSK/MTS/SBN


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