Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 191129
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
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 whether or not there is
going to be and precipitation with this. 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
concerns.

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).


&&

.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.



&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Freeze Watch from late tonight through Tuesday morning for
     ORZ021-022.
     Winter Weather Advisory until 10 AM PST this morning for
     ORZ021-022.
     Freeze Warning until 9 AM PST this morning for ORZ021-022.
     High Surf Advisory until 4 AM PST early this morning for
     ORZ021-022.
     Winter Weather Advisory until 10 AM PST this morning for
     ORZ023>026.

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
     PZZ350-356-370-376.

$$

BMS/BMS/JRS


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