Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 252227
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
227 PM PST Sun Feb 25 2018

.DISCUSSION...

.Short Term...Tonight through Wednesday Night...With large scale
ridging to our west and deep troughing over the central US, we
remain locked under north to northwest flow aloft. This keeps us
right in the middle of the fast lane as far as storm systems go,
and several of them will blow through over the next week. The
first of these is arriving this afternoon and evening, and RADAR
imagery this afternoon already shows precipitation coverage
increasing with each scan. Snow levels have risen to above 2000
feet, but will drop down to below 1000 feet on the back side of
the cold front this evening and tonight. Much of the
precipitation will be through by the time the snow levels make it
to the valley floors, but some light snow is still possible in
Medford, Grants Pass, and Roseburg before sunrise. Snow will
continue through the evening and overnight in the Cascades, across
the East Side, and in Northern California, while moderate to
heavy rain falls along the coast and the lower coastal valleys.
For more details on the expected snow amounts and timing, see the
winter weather message at WSWMFR.

Showers will continue across the region into Monday afternoon
with lower snow levels, but amounts will be light and limited to
a trace to a few tenths of an inch. Weak high pressure will build
in Monday evening through Monday night, clearing out showers but
not providing much of a break until the next system arrives
Tuesday afternoon. Models have not been consistent with the exact
timing or track of this next storm, particularly concerning the
surface low to the north and the passage of the front through our
area, but there is good agreement on the pattern and there has
been some consistency with the general nature and strength of the
system.

Th warm front arrives Wednesday, producing some light
precipitation with snow levels rising to roughly 3500 to 4000
feet. The cold front will follow quickly behind Wednesday evening
and night, and this will produce the bulk of the rain and snow as
it pushes through. Snow levels are expected to drop on the back
side of the front, but only down to about 2000 feet or so, and
only after the main bands of precipitation have moved through. We
expect another good dumping of snow in the mountains, with a good
dousing of rain below the snow line. The front is also likely to
produce gusty winds along the coast, in the Shasta valley, and
across the East Side, which could be a concern if the models tend
stronger. Again the details are not set in stone, and there are
likely to be changes, so stay tuned over the next day or so as
confidence improves. -BPN

.Long Term...Thursday through Sunday...Model solutions show good
agreement with an upper trough dropping down from the north on
Thursday, and the trough axis becoming centered along or just west
of the coast. This will bring a cold and showery pattern to the
area Thursday and Thursday night. The trough will remain in place
over the region Friday and another disturbance may move around the
trough and into the area. The main energy with this trough will
shift eastward on Saturday. However, a shortwave trough may
continue to bring showers into the area through Sunday. Zonal flow
aloft develops Saturday night and another disturbance moving into
the area with in west flow aloft may bring continue chances for
showers.

The main concern late in the week will be with lowering snow levels
and the potential for significant snow accumulations. As the upper
trough moves into place on Thursday, expect widespread showers with
lowering snow levels. Models continue to show snow level lowering
from around 2500-3000 feet Thursday morning down to 1000-1500 feet
Thursday night and locally down to 500 feet elevation. This combined
with widespread showers will bring a chance of snow down to western
valley floors. There remains variability in the model solutions
though on how much precipitation will occur with showers though. So
confidence is low on snow amounts.

Friday into Saturday, expect additional shower activity and
continued lower snow levels. However model solutions vary on the
placement of the trough and track of any additional shortwave
disturbances moving into the area. This will be key in how
widespread showers are Friday into Saturday.

Expect the pattern to transition to a zonal flow pattern with a
shortwave trough to the north by Sunday. Additional shortwave moving
down from the north and an approaching low pressure system offshore
may bring some continued precipitation into the area, especially
from the Cascades west. -CC

&&

.AVIATION...25/18Z TAF CYCLE...A cold front will move southeast
through the area this afternoon into early Monday morning with
widespread mountain obscuration and mainly MVFR with occasional IFR
and VFR. Precipitation will spread across the region ahead of this
front with snow expected for LMT by late afternoon. Periods of IFR
and moderate snow may occur at LMT this evening. Snow levels will
drop everywhere behind the front beginning this evening. RBG and MFR
could see snow showers late tonight between 10Z and 14Z as
precipitation tapers off. -DW

&&

.MARINE...Updated 200 PM PST Sunday 25 Feb 2018...A cold front
will bring increasing southwest to west winds into this evening.
Behind the front, steep seas due to a dominant northwest swell will
build to a peak on Monday. Seas will subside Tuesday into Wednesday.
Then, another round of steep heavy swell will come in late Wednesday
into Thursday, with gales likely.


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 4 AM PST Monday for ORZ029>031.
     Winter Storm Warning until 4 AM PST Monday for ORZ030.
     Winter Weather Advisory until 4 AM PST Monday above 2000 feet in
     the for ORZ023-024-026.
     Winter Storm Warning until 4 AM PST Monday above 2500 feet in
     the for ORZ025.
     Winter Storm Warning until 4 AM PST Monday for ORZ027.
     Winter Storm Warning until 4 AM PST Monday for ORZ028.
     Winter Weather Advisory until 4 AM PST Monday below 2500 feet in
     the for ORZ025.
     Winter Storm Warning until 4 AM PST Monday for ORZ029.

CA...Winter Weather Advisory until 4 AM PST Monday for CAZ081>085.
     Winter Storm Warning until 4 AM PST Monday above 2000 feet in
     the for CAZ080.

Pacific Coastal Waters...Small Craft Advisory until 4 PM PST Tuesday for
     PZZ350-356-370-376.

$$

BPN/DW/CC



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