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  Forecast Discussion for Southern Oregon and Northern California  

Forecast: Forecast Discussion | 7 Day Forecast

Forecast Discussion for MFR NWS Office

FXUS66 KMFR 191634

Area Forecast Discussion
National Weather Service Medford OR
834 AM PST Mon Feb 19 2018

.DISCUSSION...This morning we`re still observing some snow showers
at the coast and over some of the Cascades and Siskiyous. Snow
shower activity will continue to diminish through the day. Roads
could be slippery through the morning hours, especially in shaded
areas that favor lingering ice.

Tonight will be the coldest night of the winter for many areas.
There is some uncertainty in how much cloud cover will affect areas
tonight, with areas west of the Cascades most likely to have high
clouds (and potentially lingering low clouds). East Side areas are
less likely to see as much high clouds, and thus we have more
confidence in the forecast of near- to sub-zero temperatures east of
the Cascades. West of the Cascades, in the valleys, a reasonable
range of possibilities tonight is the mid-teens to mid-20s given the
uncertainty of cloud cover impacts. Our current forecast reflects
the worst case, lower temperatures of this range. Additionally, at
the coast a Freeze Warning continues for tonight.

Operational models have come into better overall agreement for a
surface low pressure to move down the coast Tuesday afternoon,
skirting the coast with precipitation. Given some warming and that
this precipitation will occur during the daytime, we don`t expect
coastal snow with this system. The impacting disturbance trails
behind the low Tuesday night and Wednesday morning, potentially
bringing another round of snow to areas from the Umpqua Divide
(Sexton Pass on I-5) northward. We`ll be focusing on that in
today`s forecast package...and yet another cold system over the
weekend that will move from north to south across the forecast

Please see the previous discussion for more details.


.AVIATION...19/12Z TAF CYCLE...Along the coast and in the Umpqua
Valley...Local IFR cigs/vsbys will clear to VFR by late Monday
morning, then VFR conditions will prevail into Monday evening.
Areas of MVFR cigs will develop along the coast Monday night with
higher terrain becoming obscured.  Over the remainder of the area...
There will be local MVFR cigs/vsbys with terrain obscurations near
and within snow showers. Once the snow showers diminish, VFR
conditions will prevail through Monday night.


.MARINE...Updated 200 AM PST Monday 19 Feb 2018...Very steep and
hazardous seas will continue into Monday, then subside Monday
evening. Seas are now peaking at 20 to 25 feet and consists mostly
of fresh swell. Winds and seas will be relatively light Monday night
into Tuesday morning.

Very cold temperatures will persist over the area through Tuesday.
Snow is possible all the way to sea level early Monday morning. Sub-
freezing temperatures are possible over the waters this morning and
Monday night, especially near the coast.

Low pressure will move south along the outer waters Tuesday
afternoon and evening. Winds will shift south and increase, but they
will remain below small craft advisory levels. Offshore high
pressure and a trough near the coast will slowly strengthen
Wednesday into Thursday, bringing increasing north winds and choppy
seas to the area. Winds and seas will subside Friday.


.PREV DISCUSSION... /Issued 329 AM PST Mon Feb 19 2018/

DISCUSSION...Current RADAR and satellite imagery is showing a few
light showers across portions of southern Oregon and northern
California west of the Cascades. Traffic cameras are also showing
snow at places like Myrtle Point and over the Siskiyous. The
overall trend with these showers is that they will continue to
decrease through the morning hours. Have transitioned the winter
storm warnings to winter weather advisories for the West Side
elevations above 2000 feet, and will continue the advisories west
of the Cascades and in western Siskiyou County until they expire
at 10 AM. Although the advisories are advertising snowfall
amounts of up to two inches, those two inch amounts will not be
widespread--only occurring where the heavier showers occur. The
main concern for this morning will be icy roads for this
morning`s commute. Therefore, we are encouraging you to allow
extra time to reach your destination this morning and take it
slow. Check Oregon road conditions at www.tripcheck.com and
California road conditions at http://quickmap.dot.ca.gov. For more
information about the winter weather advisories, see the WSWMFR.

Conditions will dry out today with clearing skies. Temperatures
will remain well-below normal for this time of year, and the clear
skies tonight will allow temperatures to plummet to the coldest
they`ve been so far this year. We`re looking at temperatures in
the single digits or below zero tomorrow night for most areas in
the Cascades and east. Areas of extensive snow cover could even
see temperatures a bit colder than forecast. Meanwhile,
temperatures west of the Cascades will be incredibly cold as well.
We are looking at temperatures in the teens for the west Side
Valleys and in western Siskiyou County. Mid 20s to low 30s are
expected in the Umpqua Basin and at the coast. A freeze watch
continues for tonight, but that will likely be upgraded to a
warning once the current freeze warning for this morning expires.
For more information, please see the NPWMFR.

The next system approaches the Pacific northwest on Tuesday.
Models have flip flopped quite a bit on this system. The GFS
remains a bit more progressive with the low staying a bit further
off the coast while the ECMWF, although a few hours slower, brings
it closer to our shores. In addition, a shortwave disturbance is
forecast to dip to the south simultaneously. The interaction
between both systems will bring some precipitation, and at the
very least some cloud cover over the area. Am tending to believe
the ECMWF as the GFS and the NAM now shows the interaction between
the low and the shortwave. This combination will keep
temperatures a bit more moderated overnight on Tuesday into
Wednesday morning. So instead of teens for western valleys,
temperatures will be in the mid twenties. And instead of single
digits to below zero values east of the Cascades, temperatures
will be in the low teens. On the other hand, this system also
provides the potential for another light low elevation snow event.

After the system moves south out of the area, another quick break
is forecast before the next system arrives on Thursday and again
into the weekend. Timing and position differences continue with
the next system expected Thursday afternoon. The GFS is faster and
further east with the next low and would have precipitation in
the area by late Wednesday night. The ECMWF on the other hand
digs the energy offshore, bringing it into central California with
the bulk of the precipitation arriving Thursday morning and
afternoon. Although the finer details are unclear at this time,
snow levels will still be low enough to for low elevation snow

For the Saturday system the GFS is faster with the precipitation
with this system, but overall there is better agreement with the
position of this system. Like the Thursday system, snow levels
look to be similar bringing another round of low elevation snow
concerns. Have gone with a blend of the GFS and the ECMWF, as
solutions in this case tend to be somewhere in the middle.

Regarding potential impacts with the upcoming systems in the
forecast, the timing and position differences in the long term
make for low confidence in the details. That being said, it does
look like there will be multiple chances for low elevation snow.
or at the very least lower elevation pass impacts due to wintry
weather. The simple difference of the timing of each system will
have big impacts on the resultant weather. If a system comes
through at night, there will be a better chance for accumulating
snow, especially for low elevations. On the other hand, if the
bulk of the precipitation moves through during the day, the
relatively higher February sun angle will limit accumulations due
to day time heating and warmer road surfaces. Stay tuned as
details become clear. -Schaaf/ BR-Y (for long term).


OR...Freeze Watch from late tonight through Tuesday morning for
     Winter Weather Advisory until 10 AM PST this morning for
     Freeze Warning until 9 AM PST this morning for ORZ021-022.
     Winter Weather Advisory until 10 AM PST this morning for

CA...Winter Weather Advisory until 10 AM PST this morning for CAZ080.

Pacific Coastal Waters...Hazardous Seas Warning until 7 PM PST this evening for



NWS MFR Office Area Forecast Discussion