Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 220454

Area Forecast Discussion
National Weather Service Reno NV
854 PM PST Tue Feb 21 2017


The low-level frontal band remains nearly stationary across the
I-80 corridor with bands of heavy precipitation continuing across
much of the Sierra, northwest Nevada, and northeast California.
Overall, precipitation is falling as snow, but a few pockets of
rain continue in valleys below 4000 feet with a mix between
4000-4500 feet. As temperatures cool into the night, expect that
roads will become icy with difficult travel conditions likely for
the Wednesday morning commute. Based on high resolution guidance
and upstream radar/satellite observations, snow will begin to
taper off overnight, with most areas clear by daybreak Wednesday.
However, another weak wave will bring a few showers during the day
Wednesday. These will be hit or miss and mainly focused north of
Highway 50 with minimal additional accumulation.

As far as the rivers, the Middle Fork of the Feather River near
Portola continues to climb and is currently between moderate and
major flood stage. The current forecast has the river just
touching major flood stage by Wednesday morning. The Pit River
near Canby is just over flood stage at this time and is beginning
to level off. Flood warnings remain in effect for both rivers and
their downstream locations. -Dawn


.PREVIOUS DISCUSSION... /Issued 324 PM PST Tue Feb 21 2017/


A powerful storm will continue to bring snow and breezy
conditions through tonight. Snow levels will drop to the valley
floors by this evening with difficult commutes likely for many
areas this evening and Wednesday morning. Lighter snow showers may
linger through Wednesday night, mainly north of I-80. Cold
conditions will continue into the weekend, when another storm
could bring widespread snow even to some valleys.

The historic winter continues with more heavy snow tonight. The
last significant wave with the trough will move through this
evening bringing heavy snow to the Sierra and also portions of
Western Nevada. Heavy convective precip bands have been forming
all day in Central CA and moving ENE in the mean flow. These have
had no problem spilling over through the 395 corridor today and it
will continue this evening. If anything, they will become more
widespread this evening before diminishing after midnight.

The strong forcing for the wave from the right entrance region of
the jet and an unstable atmosphere will be favorable heavy snow,
with snowfall rates up to 2 or even 3 inches per hour. In
addition, the area favored for the heaviest bands is along the
I-80 and Highway 50 corridors as the low level front remains
stalled there through the evening. We have increased additional
snowfall amounts for tonight and another 2 feet in the Sierra is
possible for tonight, mainly around the Tahoe Basin. Into Western
NV, up to a foot of snow is possible in any persistent heavy

After this wave moves through tonight, the main trough axis passes
through Wednesday with snow showers becoming more isolated. It
will be quite cool with brisk NW winds and temps running a good 10
to 15 degrees below average.

Northwest flow will continue on the backside Thursday into Friday
with the cold temperatures continuing. Depending on the amount of
clearing Thursday night, Friday morning could be quite cold. As
far as snow showers, they will remain isolated at best south of a
Susanville to Gerlach line. North of there it will be more
scattered with any accumulation remaining very light. Wallmann

Long Term...Saturday through next week...

Wow, this winter just won`t stop. A very dynamic weather pattern is
developing for next weekend. The phasing of two upper level low
pressure systems is forecast to draw moisture from another
atmospheric river into the west coast. I know, many of you don`t
want to hear about anymore atmospheric river storms, but here we go.

The dynamic nature of the low pressure phasing together could make
this forecast tricky for the next few days. There is currently a
wide range of possible outcomes for this system. A wave breaking
event in the central Pacific will create a cutoff low that could
make it far enough south to entrain sub-tropical moisture. The
current model simulations then bring a low pressure wave out of the
eastern Gulf of Alaska and allow these two systems to merge. This
could bring another strong winter storm into the region. However,
like I said, uncertainty will be higher than normal with this system
due to the fact that the current model forecast deals with two
separate low pressures systems (one cutoff from main flow pattern)
and atmospheric river.

It would only take a slight change in forecast track of one of these
systems for the brunt of the storm to miss the region as well.
Current simulations also show relatively cold storm, but changes in
the track and the warm moisture source this could also change. So,
the best recommendation at this time is to prepare for a significant
storm this weekend, and enjoy the quite weather if it doesn`t
materialize. -Zach


Strong bands of convective precipitation are continuing to move into
the Sierra and western Nevada today. Heavy snow will continue to
impact KTRK/KTVL/KRNO/KCXP through tonight. Snowfall rates of up to
2 inches per hour will be possible at times during the heavier bands
of snow. Sierra terminals could see significant additional
accumulations of 6-12 inches with 2-6 inches at KRNO/KCXP with
higher amounts possible on under persistent bands. KMMH could also
see a strong burst of snow, but the duration should be shorter with
less convective activity expected in Mono county.

Winds of 10-20kts occurring with heavy snow will create very low
visibility at times of less then 1/4 mile. Best estimate currently
is that conditions will begin to improve by 08-12Z. -Zach


.REV Watches/Warnings/Advisories...
NV...Winter Storm Warning until 4 AM PST Wednesday NVZ002.

     Winter Weather Advisory until 4 AM PST Wednesday NVZ003.

CA...Winter Weather Advisory until 10 AM PST Wednesday CAZ071.

     Winter Storm Warning until 4 AM PST Wednesday CAZ073.

     Winter Storm Warning until 4 AM PST Wednesday CAZ072.



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