Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 211711
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
911 AM PST Tue Feb 21 2017

Updated marine and aviation sections.

.AVIATION...21/18z TAF CYCLE...VFR conditions with local MVFR cigs
in showers will persist into this evening with areas of higher
terrain obscured.  MVFR cigs/vsbys will increase tonight as showers
persist and gradually change to snow showers over the inland areas.
Freezing levels across the area will drop to 2000 feet elevation
tonight and to 1000 to 2000 feet tomorrow morning. The lower
conditions will persist through mid-morning Wednesday. -JRS

.MARINE...Updated 900 AM PST Tuesday 21 February 2017...West to
northwest winds will gust to small craft levels through this
afternoon with steep seas. There will be periods of moderate to
locally heavy showers through today with a slight chance of
thunderstorms south of Cape Blanco. Winds and seas will lower by
early this evening. However, increasing northwest winds and seas are
expected Wednesday night into Thursday, with seas building to at
least small craft advisory levels during this time. This active
wet weather pattern will continue through the week. -JRS

&&

.PREV DISCUSSION... /Issued 848 AM PST Tue Feb 21 2017/

DISCUSSION...Updates will be sent over the next hour or so,
primarily to address headlines.

The basic situation is that we have a stacked low pressure system
roughly over Coos Bay at this time which will be moving off to
the north. This will allow gradients to weaken and general winds
to diminish on the west side. It will remain breezy to windy east
of the Cascades, which is currently covered with wind warnings and
advisories. Plenty of showers will continue in this system`s
wake, especially this morning and especially in upslope areas.
Models also show considerable instability, so it wouldn`t be
surprising to see a few lightning strikes today. Radar shows
lots of showers ongoing, and high resolution models show this
continuing through the morning, then tapering off during the
afternoon. As precipitation is showery in nature, I don`t expect
much more potential for flooding, so current areal flood watches
will be dropped. Cameras show snow occuring over the mountains and
on the east side, and thus the winter weather headlines we have
there look on track. Many updates will be forthcoming. -Wright

PREV DISCUSSION... /Issued 453 AM PST Tue Feb 21 2017/

DISCUSSION...
Yet another impressive low pressure system is moving through the
forecast area this morning with more rain, wind, and mountain
snow. The surface low pressure center moved onshore near
Brookings around 0900Z / 1AM PST. Cold air advection at the mid
and upper levels will continue into Thursday morning. 500mb
temperatures near -27C this morning will fall to a frigid -39C by
Thursday morning.

Rainfall rates overnight were occasionally 0.25" to 0.50" per hour
along and near the coast and in Western Siskiyou County. One
report of 1.05" in one hour came in from Flynn Prairie in the
Curry Coastal Mountains. Snow levels have been slow to fall, thus
far, this morning at about 3500 feet near the Coastal Mountains
to 5500 feet in Modoc County. A cluster of thunderstorms formed
northeast of Shasta Lake, but weakened before moving into Siskiyou
County. The Pit River near Canby has now risen past action stage.
A flood watch is in effect for this forecast point, and the
current expectation is for minor flooding there late this
afternoon through Wednesday morning. The Rogue River at Agness is
expected to reach action stage late this afternoon through
Wednesday. Of note, Bear Creek at Medford is nearing 7.5 feet and
action stage is 8 feet.

Showers and possibly isolated thunderstorms with gusty winds are
expected this morning, with showers diminishing in coverage this
afternoon. Areal flood watches remain in effect for portions of
Siskiyou, Josephine, the coastal counties through 10 am PST due to
the concern of training showers and isolated thunderstorms
combining with continued run-off to push some streams and creeks
possibly out of their banks. In Siskiyou County mid-elevation snow
melt is still a contributing factor. Snow levels will fall to
near 3000 feet this evening, and then into the 1500 to 2500 foot
range Wednesday morning. Winter headlines remain out, and have
been updated with the latest snow level, additional accumulation
amounts, and winds. On the east side those headlines mostly remain
for wind, falling snow levels, but minimal additional
accumulations. Pulses of showers are expected to move through the
forecast area through at least Thursday morning. Current
headlines focus on the current low pressure system, but expect
advisories for snow will be needed in some areas over the next 3
days or so. BTL

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning until 4 PM PST this afternoon for ORZ030-031.
     Winter Weather Advisory until 4 PM PST this afternoon for
     ORZ030.
     Wind Advisory until 4 PM PST this afternoon for ORZ029>031.
     Winter Weather Advisory until 10 PM PST this evening ABOVE 4000
     FEET for for ORZ027-028.

CA...High Wind Warning until 4 PM PST this afternoon for CAZ085.
     Wind Advisory until 4 PM PST this afternoon for CAZ084-085.

Pacific Coastal Waters...Small Craft Advisory until 4 PM PST this
     afternoon for PZZ350-356-370-376.

$$



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