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fxus66 kmfr 260148 

Area forecast discussion
National Weather Service Medford or
548 PM PST Sat Feb 25 2017

the marine and aviation sections have been updated.


Aviation...26/00z taf cycle...
mostly clear skies are expected this evening, except in the higher
mountains where dissipating cumulus result in diminishing partial
terrain obscurations. Late this evening through sunrise Sunday rapid
radiational cooling is expected to result in areas of IFR to MVFR
low clouds and fog across the valleys. Confidence in this fog and
low cloud formation is moderate because the pattern suggests it will
occur, but the model guidance only vaguely hints at it. After
midnight some light rain/snow is expected to begin with MVFR
conditions across Coos and Douglas counties, with snow levels 500 to
1000 feet and the terrain obscured. As the cold front moves
southeastward Sunday, followed by the upper level low aloft, MVFR to
IFR conditions are expected in precipitation across the area, with
terrain obscurations increasing. There will be a threat of
thunderstorms over the coastal waters eastward into the Coast Ranges
Sunday afternoon and evening. Btl


Marine...updated 320 PM PST Saturday, 25 February 2017...
high pressure will weaken tonight as another cold low pressure
system approaches. Showers will then begin Sunday morning as gusty
southwest winds develop and short period seas build. Winds are
expected to become west-northwesterly during the afternoon, and
there is a slight possibility of thunderstorms Sunday afternoon
and evening. Fresh swell will cause steep seas Sunday morning to
become very steep Sunday afternoon and night. Showers continue on
northwest flow through Monday night as seas remain steep. High
pressure will begin to build in Tuesday. Btl


Previous discussion... /issued 257 PM PST Sat Feb 25 2017/


Short term...tonight through Tuesday night...the region has
mostly cleared today under shortwave ridging, with sun shining in
all but those areas where cumulus fields have formed. Dry and
fair conditions will continue through this evening, then clouds
will begin to increase tonight ahead of the next low pressure

Not a lot has changed regarding the features and expected weather
associated with this next low, which will drop south along the
Pacific northwest coast and pass almost directly over southern
Oregon and northern California. With the prevailing low and mid
level winds form the west, upslope flow will combine with the
system's dynamics to produce precipitation across the region
Sunday morning into Sunday evening. With snow levels beginning
the day at 500 to 1000 feet, and only rising to around 1500 feet
during the day, much of the region will see snow. Accumulations
are much harder to nail down, especially as ground and Road
temperatures may be too warm at first to allow much of the snow to
stick. However, given the setup and the precipitation that does
continue into the evening and overnight, have refined and
upgraded the winter weather headlines, which cover the bulk of the
Cascades and points west, and also include a small portion of the
east side and northern California. Many, if not all, of the area
passes will be impacted, and travel may be troublesome Sunday
into Sunday night. Some of the west side valley floors may even
get in some light snow as well. For more details on these
advisories and warnings, see the winter weather message at

While the surface low will exit the region Monday, the upper level
trough will slow down in its progression, and will not fully
leave the area until Tuesday morning. This continued cyclonic flow
aloft will keep clouds and showers in place through Monday night,
and temperatures will remain cool with snow levels between 500
and 1500 feet. Conditions should improve Tuesday once high
pressure begins to reestablish itself.

Long term...Wednesday through Saturday...things will start off
fairly quiet with a broad area of high pressure building over the
area from Wednesday until Thursday. We'll eventually see a mature
low off the Gulf of Alaska slide south and produce scattered to
widespread rain along a cold front boundary. Both models are in
pretty good agreement with the timing of this, so have high
confidence some rain is on the way Friday evening. Eventually,
this low will combine with another low to pull even more moisture
in from the tropics.

We have high confidence tropical moisture will hit US in the Pacific
northwest next weekend around the Saturday Sunday time frame. Still
not sure about the exact timing or location at this point as it's
dependent on a low from Russia pulling up some moisture when it
moves over the Hawaii region, but since it's being observed, and
both models are showing rain next weekend, feeling pretty good about
the forecast at this point.

The only other note is that snow levels are expected to be around
the 5000 to 8000 foot level as there is warm moist air crashing
against the Cascades Saturday to Sunday. So we'll have to watch out
for a Cascade snow event if snow levels drop a bit lower. Stay tuned.


Mfr watches/warnings/advisories...
or...Winter Weather Advisory from 10 am Sunday to 4 am PST Monday for
Winter Weather Advisory from 7 am Sunday to 4 am PST Monday for
Winter Storm Warning from 10 am Sunday to 4 am PST Monday for
Winter Weather Advisory from 10 am Sunday to 4 am PST Monday for
Winter Weather Advisory from 10 am Sunday to 4 am PST Monday for

California...Winter Weather Advisory from 7 am Sunday to 4 am PST Monday for
Winter Weather Advisory from 10 am Sunday to 4 am PST Monday for

Pacific coastal waters...
- Small Craft Advisory for hazardous seas from 1 PM Sunday to 4
am PST Tuesday for pzz350-356-370-376.
- Small Craft Advisory from 7 am to 1 PM PST Sunday for pzz350-370-376.

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