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Area forecast discussion 
National Weather Service Medford or
808 PM PST sun Jan 25 2015

Discussion...another night under high pressure, another night
without any necessary updates to the public forecast. It will also
be another night of watching for dense fog under the rather
strong valley inversions. The past two mornings have seen
significant fog, and tomorrow morning does not appear that much
different. Updates will be issued when needed. For more
information, please see the previous forecast below. -Bpn


Aviation...based on the 26/00z taf cycle...satellite shows stratus
about 25 miles off the coast this evening, and models bring it near
the north coast by around 26/12z. Fog/stratus with IFR ceilings/MVFR visible
is also expected to form locally along the coast prior to that. It
will likely burn off fairly quickly Monday morning. Fog with LIFR
ceilings/visible is also expected to form in west side valleys again around
dawn Monday and last through late morning. Elsewhere, VFR
conditions will continue for the next 24 hours. -Wright


Marine...updated at 745 PM Sunday 25 January 2015...swell has not
been as high as expected this evening and will continue to diminish
tonight, so the Small Craft Advisory has been dropped. South winds
will increase through Monday as a low pressure moves by to the
north, however winds will remain below Small Craft Advisory levels.
A weak front moves over the waters Tuesday and then dissipates over
the area on Wednesday which will lead to light and variable winds
during the period. Moderate northerly winds are expected Thursday
into Friday as high pressure builds in to the north. -Wright

Previous discussion... /issued 227 PM PST sun Jan 25 2015/

Short term...the strong high pressure ridge over the area will
linger into Monday as it gradually shifts eastward. This pattern
will bring continued strong valley inversions, breezy southeast
winds on the ridges, and areas of nighttime and morning valley
fog. Then the high pressure will weaken on Tuesday with a Pacific
front moving into the coast from the west and a low moving up into
northeast California.

Valley fog is expected to redevelop tonight in inland west side
valleys with similar conditions as today. Dense fog may be
possible once again, especially in Valley West of the Cascades in
southern Oregon, including the Umpqua, Illinois, Applegate and
rogue valleys. Clearing is expected during the day.

High temperatures on Monday are expected to be slightly less warm
than today but otherwise expect another warm and sunny day for
inland areas. Air stagnation conditions will continue on Monday
and into Tuesday morning for inland valleys as valley inversions
continue and there is little vertical mixing.

Along the coast, south winds will continue tonight into Monday.
Expect some areas of marine stratus to push into the marine waters
tonight. Then the NAM model indicates that marine stratus may
extend to portions of the coast Monday afternoon and evening,
initially from Cape Blanco northward, then over much of the coast
Monday night.

On Tuesday, the pattern will begin to change with high pressure
weakening and cooler conditions developing as a weak Pacific front
moves towards the coast and a low moves up into northeast
California and Nevada. The low is expected to bring a chance for
precipitation to southeast portions of the area on Tuesday. Models
continue to show the best chance for precipitation over eastern
Siskiyou, Modoc and southeast lake counties Tuesday afternoon and
evening. Along the coast, the weak Pacific front is forecast to
slowly push towards the southern Oregon coast Tuesday afternoon
and Tuesday evening, stalling along the coast Tuesday night into
Wednesday morning before shifting north during the day Wednesday.
Models continue to indicate that this front will bring a chance of
very light rain to coastal areas and just inland, with the best
chance for light rain along the coast for locations north of Cape
Blanco. Also on Tuesday, expect some increased vertical mixing,
especially east of the Cascades with a period of no air stagnation
in the valleys. Models also indicate that mixing may improve in
west side valleys as well. Currently have the air stagnation
advisory out through Tuesday morning.

On Wednesday and into Wednesday night, a high pressure ridge will
begin to rebuild over the region. However the high pressure may
remain relatively weak with a weak trough persisting off the
California coast. With the return of high pressure may see air
stagnation conditions return to inland valleys Wednesday or later
in the week.

Long term...Thursday through Sunday...upper ridging will gradually
build over the region through the extended forecast period and dry
weather will continue. A positively tilted ridge will lean over the
forecast area Friday into Saturday...and temperatures are not
expected to not be quite as warm as the current ridge because the
amplitude is lower...but we do believe there will be plenty of
sunshine to start the weekend. The coast and mountains can expect
temperatures to be above normal...with slightly less confidence in
west side valley warm temperatures. Given the increasing sun angle
and shorter nights...there should be less fog coverage late this
week and into the weekend...and thus temperatures should get to
above normal readings.

On Sunday the GFS hangs a front over the forecast area and suggests
precipitation for most of the area...but this is the first run that
has shown this...and the European model (ecmwf) and most ensemble solutions are dry
at this prefer the European model (ecmwf) and have kept precipitation
chances low through Sunday.

Looking further out in time...the ridge over the northwest buckles
some and shifts eastward...allowing for some upper troughs from the
west to move in...but the first of these does not look particularly
strong. So there are no major storms on the horizon. /Sk


Mfr watches/warnings/advisories...
or...air stagnation advisory until 11 am PST Tuesday for
Air stagnation advisory until 11 am PST Tuesday for


Pacific coastal waters...none.



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