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Area forecast discussion 
National Weather Service Medford or
222 PM PST Sat Nov 22 2014

Discussion...moist onshore flow will continue through this evening with
showers moving in from the west. A few isolated storms develop in
the last couple of hours in Coos and western Douglas County as a
cool pool aloft combined with daytime heating has created
sufficient instability. Could not rule out a few more isolated
storms in the same areas early this evening. Meanwhile snow
showers will continue above 4000 feet with accumulating snow
likely around crater and Diamond Lake areas. Snow showers are
likely near the Lake of The Woods, but were not expecting any
accumulation. Weak ridging builds into the area tonight and
showers will be on the decrease with most ending after midnight.
With ample moisture on the ground, low clouds and fog are likely
to develop for the Westside valleys if there's enough clearing.

Weak upper ridging moves into the area Sunday. It's not a Sharp
Ridge, but rather flat, but it should be enough to shift the storm
track north of our area and we'll end up dry. The models show a warm
front moving into the area Monday. The NAM is now the most aggressive
with respect to quantitative precipitation forecast amounts. The ec and GFS show little or nothing.
Compared to yesterday the GFS has trended weaker and the ec continues
to remain dry. Gut feeling is the NAM may be overdone given 500 mb
heights are rising as the upper ridge starts to amplify. For now
kept in slight chance to chance probability of precipitation west of the Cascades. The upper
ridge axis builds into the area Tuesday with continued dry
conditions, although the ec hints at some warm frontal precipitation
riding over the ridge and possibly bringing light precipitation to
the northwest part of the area. There's a good chance we'll have low
clouds and fog for most of not all Westside valleys given that we
have sufficient moisture on the ground and a stable atmosphere
Tuesday morning and probably again Tuesday night. -Petrucelli

Long term...Wednesday through Saturday...deterministic and ensemble
model runs continue to show good consistency in an upper ridge
holding over our area Wednesday and Wednesday night. Precipitation
will be held at Bay to our west during the period, but inversions
are likely to be strong and thus valley fog is still a good bet.

There is a bit more consistency regarding the breakdown of the ridge
and the arrival of new precipitating systems late this week into
next weekend. Ensemble means support determinstic runs which show a
trough or series of troughs coming into our area during this period.
While spreads are still higher than I would like to see, the spread
appears to have more to do with the timing of the troughs than their
existence. That said, confidence is still not high enough to go a
lot higher than climatology for pops, but I did raise pops, especially
later Friday into Saturday. -Wright


Aviation...for the 22/18z taf cycle...isolated to scattered showers
will continue over the region this afternoon. VFR ceilings and visible will
be the prevailing conditions at the terminals, but brief MVFR
conditions will be possible in showers. Moist, upslope flow will
keep mountains obscured by cloud this afternoon. As showers and
clouds diminish tonight, fog is a strong possibility in the valleys,
including all terminals. It has been introduced in all tafs, but
confidence was only high enough at the moment to go with LIFR ceilings
and visible at krbg. -Wright


Marine...gusty west winds will persist today, mainly beyond 10 nm
from shore. A cooler air mass will move in and there may be enough
instability for a few isolated storms from Cape Blanco north. Westerly
swell will increase today and continue through Sunday. A weak warm
front will arrive Monday and bring increasing south winds, but
they should remain below small craft. A fairly quiet pattern is
expected Tuesday and Wednesday, then another front could bring
increasing south winds by Thanksgiving day.


Mfr watches/warnings/advisories...
or...Winter Weather Advisory until 10 PM PST this evening for


Pacific coastal waters...Small Craft Advisory for hazardous seas until 4 PM PST Monday
for pzz350-356-370-376.


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