Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 220400

Area Forecast Discussion
National Weather Service Medford OR
900 PM PDT FRI OCT 21 2016

A weakening, shearing apart cold front is moving across the
forecast area this evening. Showers have been very isolated and
precipitation is mostly not reaching the ground with this front.
Overnight weak high pressure will build in. Light winds and
clearing skies will bring fog and low clouds to many of the
valleys around sunrise Saturday morning, mostly on the West Side.
Mild temperatures on the West Side this evening and fairly high
dewpoints will prevent frost from being a concern yet again. The
next front is due in on Sunday, but will likely take until Monday
into Tuesday to affect most of the forecast area with significant
wind and rain. Snow levels are expected to be mostly above 7kft as
this front moves through BTL


.AVIATION...22/00Z TAF CYCLE...IFR will prevail at the coast and
coastal waters, and should burn offshore late morning.

Inland...Areas of MVFR/IFR cigs are expected to return to inland
valleys west of the Cascades late this evening. Conditions will
improve around 16-18z for most locations but lingering MVFR cigs are
possible in the Umpqua Valley through late tomorrow morning. TAF
guidances are not indicating fog in the Rogue Valley, but with
clearing indicated after 6Z and a current few point of 51 at 6 pm
and an expected low of 53, have added fog for MFR. east of the
Cascades the expected low is below freezing and am expecting any low
moisture to be deposited as frost. All areas except the coast will
become VFR tomorrow afternoon. -Sven

Note: The ceilometer at FAA site KOTH is out of service, so there
will be no ceiling observations available generally between the
hours of 04Z and 14Z.


.MARINE...Updated 235 PM PDT Friday, October 21, 2016...Weak high
pressure over the region will continue generally light winds over
the waters until south winds increase ahead of an approaching cold
front late Saturday morning. These small craft advisory winds remain
through Sunday afternoon when they increase but stay below gales. An
unsettled pattern remains through mid week next week. Sven


.PREV DISCUSSION... /Issued 257 PM PDT FRI OCT 21 2016/


Short Term...Tonight through Monday Night...Radar imagery shows a
few showers working their way across he forecast area, but local
observations suggest that very little precipitation is reaching
the ground, just a hundredth or two here and there, with slightly
more in the usual wetter spots where upslope is strongest.
Otherwise, much of the area remains cloudy but dry. This will be
the case for the rest of this afternoon and into the evening.

The more active pattern will begin tomorrow night, as a
significant plume of moisture makes its way towards the coasts of
Southern Oregon and Northern California. The first front
associated with this system appears to stall out along the coast
Sunday, but showers along and ahead of it will bring some light
rain to the coast, coastal ranges, and the Umpqua basin. Winds
could get breezy at times, especially within or near showers, but
no strong winds are expected.

The next front will be more of a weather maker, and will push
inland with gusty winds and periods of heavy rain late Sunday
night into Monday morning. This will not be a particularly strong
storm, but more of a typical wet season event for the area. Expect
gusty winds along the coast, in the Shasta Valley, and across the
high terrain and East Side, with light winds in the West Side
valleys. Wind advisories may be needed in the Shasta Valley near
Weed, and for portions of the East Side, particularly along
highway 31 near Paisley. The main belt of heavier rain will
arrive at the coast before daybreak Monday morning, spread east
to the Cascades by midday, then across the East Side during the
afternoon and evening. Once the front passes, showers will linger
into Tuesday morning.

While not as potent  a feature as the atmospheric river last
week, model depictions of the onshore moisture flow with this
system are not weak either. The Southwest Oregon coast near
Brookings will get the bulk of the precipitation, with up to 4 or
5 inches possible by Monday night. West of the Cascades, expect up
to an inch, except in the Rogue and Shasta Valleys where up to a
half inch is likely. East of the Cascades, amounts should total
more towards a quarter inch. Snow levels throughout the event
should remain above pass levels, although in heavier
precipitation, snow may make it down to road level in the Diamond
Lake area. Otherwise, only significant accumulations are expected
above 7000 feet.

From now through  Monday night, temperatures will cool slightly,
but should remain at or just slightly below seasonal normals. -BPN

LONG TERM...Tuesday through Friday...Models are in good
agreement that a long wave upper trough will remain entrenched
over the northeast Pacific early to mid next week. A warm front
will bring widespread rain to our area Tuesday, and while the
models do vary in the amount of precipitation, all of our area
should receive some rainfall Tuesday with the greatest focus in
the south and western areas. Snow levels look too high to have any
impact in our area except possibly at Crater lake at the
beginning. Models also show a surface low/triple point forming in
the diffluent area of the upper trough and moving south to north
through or just west of our waters. Although this is a new
development in the models and they disagree on the timing, they
all show gales in our waters some time between Tuesday night and
Wednesday. We judged it wise to increase the winds over our waters
during this period. It was also prudent to increase winds on the
east side, although they will probably need to be much higher than
we currently have as we get more confident.

Later Wednesday, precipitation starts to diminish over much of
our area. However, a weak atmospheric river remains aimed at
Curry, Del Norte, and Siskiyou counties, so rain will likely
continue through the day Wednesday over the usual wet spots. By
Thursday, a big slug of energy dives into the trough further south
and begins to form a cutoff low well off California. This
introduces a split in the flow, which may dry us out Thursday, but
models all quickly eject this low inland over us Friday.
Confidence is not usually high in general with cutoff lows, but
fair model consistency exists, so we`ve kept at least chance pops
in during the period. -Wright




Pacific Coastal Waters...
- Small Craft Advisory from 5 PM Saturday to 5 AM PDT Sunday for
- Small Craft Advisory for hazardous seas until 5 AM PDT Sunday
  for PZZ350-356-370-376.


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