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Area forecast discussion
National Weather Service Medford or
1025 PM PST Wed Feb 22 2017

an update has been sent to fine tune overnight lows, rain and snow
amounts, and winter weather headlines for tonight through
Thursday morning. Btl


radar and Road cameras indicate 3 remaining areas of notable snow
shower activity at the current time. These are between Mount
Shasta and the California border including Highway 97, in the
Applegate and rogue valleys, and in the coastal mountains. Higher
resolution models are in fairly good agreement that these 3 areas
of showers will result in an additional inch or less of snowfall
above 1500 feet through 1 am PST. These same models also indicate
precipitation tapering off to just snow flurries at most from 1
am PST through Thursday morning. Therefore, we have adjusted
expiration times of the current winter weather advisories on the
west side to 1 am PST. The advisory for the Curry coastal
mountains above 1500 feet has been extended to 1 am PST. The
advisories that had been in effect for much of Siskiyou County,
the Cascades, and Siskiyous have been allowed to expire.

While snow will come to an end for most areas after midnight,
temperatures will fall below freezing at all locations that have
gotten snow and for some lower elevation areas that have not.
Thus, untreated roadways will become slick in some areas Thursday
morning until temperatures warm above freezing. Btl


Previous discussion.. /issued 820 PM PST Wednesday Feb 22 2017/

Evening update...snow is falling down below 2000 ft but only mixing
with rain at times down to the Airport in Jackson County. Looking at
webcams around the region the current forecast looks on track, and
other than making some minor adjustments to the 6-12z quantitative precipitation forecast the
current forecast looks on track. Sven


Short term...tonight through Saturday night...several reports of
graupel and snow have been called into US today from Roseburg,
Oregon to Etna, California. This suggests that snow levels remain
relatively low in general, but have also been highly influenced
by the strength of the showers. This trend is expected to continue
through the rest of the week. Although there have been some
breaks in the clouds west of the Cascades which have helped melt
the snow and graupel after the showers have passed, colder
temperatures will return tonight and accumulating precipitation
may take longer to melt. Have decided to allow the winter weather
advisories to continue through their expiration times.

The weather is expected to remain in this showery and cold
pattern for the rest of the week. Although things briefly reprieve
on Thursday, the next low pressure system will be sliding down the
West Coast on Friday and Friday night. The 12z run of the GFS and
the 12z European model (ecmwf) align quite nicely with the details of the track and
the strength of this low. The preliminary 18z run of the GFS,
however weakens this system. With this teeter-tottering of the
GFS, have gone with a blend that favors the European model (ecmwf) solution. Have
even further upped the quantitative precipitation forecast at the coast, the Siskiyous, and the
Illinois Valley on Friday night because the low will be positioned
to draw in extra moisture in these places. Snow levels will remain
low, and with the stronger showers that occur in these area,
periods of heavy snow will be possible. Confidence is only so-so
because if the track of the low moves further toward the coast,
the heavy snows could even make it to the Rogue Valley. If the low
tracks further off the coast, less snow would occur. Have issued a
Winter Storm Watch for a few of these areas closer to the coast
(but not including the rogue valley). Because the newest model
runs are differing somewhat, this situation will definitely need
to be monitored.

Things east of the Cascades will be more typical for February with
mainly drier weather and cold temperatures. Lows are expected to
be in the teens for many areas while highs struggle to reach into
the mid 30s. -Schaaf

Long term...the models are in pretty good agreement through
early next week. Another upper trough is projected to move south
along the Washington/Oregon coast during the day Sunday (similar
to the one on Friday night/Saturday morning). The only difference
is this one is expected to come in during the day which should
lessen the threat for lower elevation snow, but it still exist due
to a combination of existing cold air in place and precipitation
rates which if high enough could drag the snow level down lower
than what's in the forecast. Right now, we have snow levels around
2000 feet on Sunday, but it could end up lower in heavier
precipitation. Also given it's still a few days out, details on
the exact track of the low could change. For example, in northerly
flow events, the models are typically too slow with the arrival
of these systems, therefore it would not be out of the realm of
possibility precipitation could move in overnight Saturday into
Sunday morning. At this point its too early to speculate on timing
and track of the upper low and snow amounts, but it's something
that we'll have to watch closely.

We'll see some improvement in the weather Monday, at least in terms
of precipitation with most of it focused in northern California and
east of the Cascades. It will remain cool to cold with showers
decreasing from north to south during the day. A cool northwest flow
will continue Tuesday. The models still hint at some qpf, but
suspect this may be overdone given 500mb heights will be on the rise
and any shortwave activity should stay east of our forecast area.

Wednesday looks dry as an upper ridge starts to build into the area
and the storm track shifts well north of the area. -Petrucelli


Aviation...23/00z taf the coast, mainly VFR conditions
are expected with scattered showers through Thursday afternoon.
Elsewhere, VFR conditions will prevail but conditions in scattered
showers could be as low as IFR in snow showers into Thursday.
Mountain obscurations will also occur. VFR conditions will prevail
Thursday afternoon although isolated to scattered rain and snow
showers will cause brief MVFR-IFR conditions.


Marine...updated 235 PM PST Wednesday 22 February 2017...the
latest buoy observations showed seas of 8-9 feet at 12 seconds.
Winds were generally below 15 knots except for the southern waters
near the Oregon-California border which were mainly 15-20 knots.
There were also heavier showers causing higher wind gusts. Steeper
seas are expected to develop from west to east tonight as the
dominant period will steepen to 8-9 seconds. Seas will be around 8
feet at 8 seconds tonight into Thursday morning so the Small Craft
Advisory in effect for hazardous seas looks reasonable, although
marginal. Seas steepness will subside on Thursday. Low pressure
moving down the Pacific northwest coast on Friday should increase
winds and steepen the seas with possible small craft conditions
developing. Sandler


Mfr watches/warnings/advisories...
or...Winter Weather Advisory until 1 am PST Thursday above 1500 feet
for for orz021-022.
Winter Storm Watch from Friday morning through Saturday morning
for orz021-022.
Winter Storm Watch from Friday morning through Saturday morning
for orz023>026.
Winter Weather Advisory until 1 am PST Thursday for
Winter Storm Watch from Friday morning through Saturday morning
for orz028.

California...Winter Storm Watch from Friday morning through Saturday morning
for caz080-081.
Winter Storm Watch from Friday afternoon through Saturday
morning for caz082-083-085.

Pacific coastal waters...
- Small Craft Advisory for hazardous seas from 4 am to 10 am PST
Thursday for pzz350-356.
- Small Craft Advisory for hazardous seas until 4 PM PST Thursday

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