Area Forecast Discussion
Issued by NWS Medford, OR

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378
FXUS66 KMFR 231628 CCA
AFDMFR

Area Forecast Discussion...CORRECTED
National Weather Service Medford OR
828 AM PST Mon Jan 23 2017

Aviation updated...

.DISCUSSION...
A cold upper level low will move southeastward from west of the
coast near 130W and into Central California through Tuesday. As
this occurs showers will wind down along and near the coast and in
Northern California. With the cold air aloft, a brief shower is
possible elsewhere, but these should be only isolated in the
valleys to scattered in the mountains. High pressure will build
in today through Tuesday leading to cool conditions through mid-
week. The current forecast covers this well, so no updates are
needed this morning. BTL

&&

.AVIATION...23/18Z TAF Cycle...The biggest aviation impact
this morning is fog and freezing fog, affecting Klamath Falls and
Medford. We have amended the TAFs to keep fog in through the early
morning hours. Conditions should improve later this morning.
Isolated to scattered showers will continue through today. There
will be areas of MVFR cigs with higher terrain obscured...becoming
isolated this afternoon. All areas will become VFR early this
evening...but areas of IFR cigs/vsbys in fog and freezing fog will
develop again over the valleys late tonight into Tuesday morning. SK

&&

.MARINE...Updated 145 AM PST Monday 23 January 2017...A weakening
low will move south along 129W today off the southern Oregon coast.
It will move south of the area this evening and weak high pressure
will develop over the waters.  Seas will remain very steep through
Monday evening...then steep through Tuesday morning. High pressure
will weaken Wednesday and a weak front will move onshore Wednesday
night. Moderate westerly swell will also move through Wednesday
night into Thursday night. High pressure will return Thursday and
persist for the rest of the week.

&&

.PREV DISCUSSION... /Issued 153 AM PST Mon Jan 23 2017/

DISCUSSION...The vertically stacked low continues to spin just
offshore of the Pacific Northwest, and will gradually begin to
slide south through today and into tonight, eventually exiting the
area by tomorrow morning. Until then, rain and snow showers will
continue to pass over our region. The upslope flow over Sikiyou
County will continue as well, producing more snow accumulations
through this morning. Compared to the past 24 hours, these amounts
will be very light, but enough to keep a winter weather advisory
in place. For more details, see the Winter Weather Message, or
PDXWSWMFR.

The region will finally see a relatively long stretch of quiet
weather begin Tuesday and persist through this week and into this
weekend. Only one weak system will try and make its way inland
during this time, most likely around Wednesday afternoon and into
Thursday. With high pressure in control, the arriving front will
weaken considerably and stall out over the Cascades and East Side.
There is not much in the way of precipitation or winds expected
to arrive with this front, and most of the region will mark it as
only a cloud and very light rain/snow producer. Dry weather will
then continue through the remainder of the forecast term.

Two things will be of concern during this time, and both center on
the valley inversions that we typically see under high pressure
this time of year. Fog and low clouds will be the first issue, and
may be dense at times, and in areas where the temperature drops
below freezing, will pose a freezing fog threat. Fog is a
troublesome forecast element, and confidence is not high at any
time range other than extremely near-term. The second issue may
be air stagnation, which would result due to the low mixing and
weak winds, mainly after the weak front passes Wednesday and
Thursday. This would allow particulates and other pollution to
collect in the valleys, and may become a problem for those with
sensitive respiratory systems. More details on these issues will
be forthcoming later this week. -BPN

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Surf Advisory until 10 PM PST this evening for ORZ021-022.

CA...Winter Weather Advisory until 10 AM PST this morning for CAZ081.
     Winter Weather Advisory until 10 AM PST this morning ABOVE 2000
     FEET for for CAZ080.
     Winter Weather Advisory until 10 AM PST this morning for
     CAZ082-083.

Pacific Coastal Waters...
- Small Craft Advisory for hazardous seas from 10 PM this evening
  to 10 AM PST Tuesday for PZZ350-356-370-376.
- Hazardous Seas Warning until 10 PM PST this evening for
  PZZ350-356-370-376.

$$

BTL/BPN/JRS



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