Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 242312

Area Forecast Discussion
National Weather Service Medford OR
312 PM PST Tue Jan 24 2017

A long wave trough continues to exit the region leaving behind
mainly clear skies and rather pleasant weather. After this wave
moves out, a weak front will push towards the region generating a
chance of precipitation Wednesday night. Precipitation is
expected to be light, so no major concerns with snow levels around
2000 to 3000 feet.

After the front moves through,  we have high confidence that high
pressure will build and continue through the weekend.  Winds are
expected to remain light with poor vertical mixing through the
atmosphere.  It should be noted that the Westside valleys appear to
mix air up to 1500 feet at times.  However, we have noted in the
past that models can do poorly with inversions in the winter, so we
leaned towards issuing the air stagnation advisory today.

Other than stagnant air,  temperatures will remain near normal for
this time of year.  In addition, we`re expecting fog to develop in
the valleys every night except Wednesday night.


The stagnant air mass will persist through Saturday night with a
broad upper level ridge still extending from offshore of California
northeastward across the western states. This will also result in
continued cold morning lows, areas of morning (mainly west side)
freezing valley fog, and a warming trend of high temperatures.
Of those items, the most noteworthy is arguably east side valley
morning low temperatures which will be in the single digits to
possibly below zero.

By Sunday, there is less confidence in the details of the forecast
but a good general idea of the evolution of the pattern. A trough is
expected to track east into western Canada and weaken the ridge. The
southern edge of a front will weaken as it reaches the Oregon coast.
The probability of rain will be higher the farther to the north that
one goes. The ECMWF is slightly stronger but has very similar timing
to the GFS. Light rain may be limited to the coast or remain north
of our area. The probability is higher for Sunday night than
during the day on Sunday. For the majority of our area, the weekend
sky cover will be an increase in high clouds.

The remainder of the long term weather will be driven by the
interaction of the lingering ridge and the next disturbance...a
closed low approaching from the west. The low is forecast to near
the coast by late Tuesday and should bring a moist but warm
southerly flow into mid-week. -DW


.AVIATION...25/00Z TAF Cycle...A stable atmosphere has settled over
the region. Currently all TAF sites are VFR, but there is still
concern for fog and/or low stratus to develop with conditions
quickly going from VFR to LIFR for Roseburg, Medford and Klamath
Falls tonight and into early tomorrow morning. Some high clouds will
move in over the area as well, and this may or may not limit fog
development. If fog does develop, VFR should return to all areas by
late tomorrow morning. -BPN


.MARINE...Updated 200 PM PST Tuesday 24 January 2017...Weak high
pressure will persist over the waters with diminishing seas into
Wednesday morning. But, a long period west swell will arrive
Wednesday morning and rapidly increase Wednesday afternoon into
Thursday while a weak front moves through. Seas are expected to
become high again by Wednesday evening with the swell peaking at
around 16 feet at 20 seconds on Thursday morning. Weak high pressure
returns Thursday, then shifts inland Friday into the weekend with
seas remaining dominated by a high and steep west swell. -DW/BPN


OR...Air Stagnation Advisory from 10 PM Thursday to 4 AM PST Sunday
     for ORZ021-023-024-026-028>031.


Pacific Coastal Waters...Small Craft Advisory for hazardous seas from 4 PM Wednesday to 4
     PM PST Friday for PZZ350-356-370-376.


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