Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 210418 AAA

Area Forecast Discussion...UPDATED
National Weather Service Reno NV
818 PM PST Fri Jan 20 2017


Heavy convection is starting to move up the Interstate 80 corridor
this evening from the Sac Valley and towards Blue Canyon. This
convective complex will bring a burst of moderate to heavy snow to
the Donner Pass area and into the Truckee-Tahoe areas tonight
between 9pm to midnight. Otherwise, the forecast looks pretty much
on track through Saturday and into the beginning of the big winter
storm coming up for Saturday night through Monday. Models continue
to show impressive amounts of snow for the Sierra and western NV,
so there is definitely strong forecaster confidence in the coming
storm. Please see the previous discussion below for additional
information about the weekend weather highlights and things you
can do to prepare you and your home for the upcoming storm. Hoon


.PREVIOUS DISCUSSION... /Issued 317 PM PST Fri Jan 20 2017/

A system will exit northeast California and western Nevada
tonight, bringing a lull in precipitation amounts for the Sierra
and a break for most of western Nevada. A much stronger system
will impact the region Saturday night through early Monday,
bringing heavy snow to the Sierra and western Nevada, with the
Sierra seeing areas of blizzard conditions. Dry but cold weather
is expected for the middle to end of next week.



*Lull in the weather (lighter snowfall Sierra/break for western NV)
 Saturday is your window of opportunity to make preparations for
 the next storm.

*Powerful winter storm to impact the Sierra AND western Nevada
 with widespread heavy snowfall Sunday into Monday.


For communities in the higher terrain: Tahoe Basin, Mono County,
and Virginia City. While there is potential for some unanticipated
impacts, such as deck, roof, or carport collapses, local officials
are extremely concerned about more downed trees across powerlines,
roadways, and into homes. Dig out and clear as much snow as possible
before the next storm moves into the area. Snow removal will become
extremely difficult as feet of snow piles up. Prepare for extended
periods of power outages, more downed trees, as well as being stuck
in your residence. Local authorities are recommending enough non-
perishable food for up to a week. Listen closely to local law
enforcement and fire officials for recommendations.

An elongated trough axis is moving over northeast California and
northwest Nevada, with some minor instability bringing a few snow
and sub-4500 foot rain or possibly ice pellet showers north of
I-80. In the Sierra, continued moist upslope flow is bringing snow
showers and one final widespread area of light to moderate snow
(with trough axis) near and north of I-80. With snow showers
sporadic and generally light in western NV, will likely drop the
winter weather advisory for the Reno-Carson City-Minden
area...especially as road temperatures are well above freezing
and mainly wet. However, keep in mind that there could be
localized areas of snow showers that persist into the evening and
some road temperatures above 5000-5500 feet could drop down close
to freezing after dark for some slick patches.

A lull in the stormy pattern will commence tonight and last
through much of Saturday evening before the main event begins. The
lull does not mean there won`t be continued light to occasionally
moderate snow in the Sierra with travel restrictions as moist and
slightly unstable upslope flow continues there. However, snowfall
amounts are expected to be comparably modest as forcing aloft
weakens. In western Nevada, isolated showers were left in the
forecast through Saturday evening with residual moisture and a
very weak wave moving overhead on Saturday. Little or no
additional snowfall is expected through Saturday evening.

Late Saturday night and Sunday morning, a combination of warm air
advection and a moisture tap with good moisture transport will
cause snow to break out in the Sierra and out into western Nevada.
With the strong warm advection pattern and fairly moist atmosphere
right from the start, spillover should not be much of an issue.
Sunday, a strong jet streak in excess of 150 kts will move over
the northern Sierra and western Nevada. This should bring plenty
of forcing for sustained spillover into western Nevada, especially
near and north of highway 50, with snowfall rates possibly reaching
2-4" per hour at times in the Sierra.

One area of concern for snowfall amounts in western and west-
central Nevada will be areas below 5000 feet. Some simulations,
especially the GFS, show warming in the Basin valleys near and
south of I-80 by the afternoon. The caveat for whether snow levels
rise or not might wind up being precipitation rates. With the
strong forcing and winds aloft to encourage spillover, valley areas
close to the Sierra will likely see sufficient rates to hold
precipitation as a heavy, wet snow. However, if there are precipitation
breaks farther out into the Basin (south and east of Reno), then
there could be a 6 or so hour period of mixed rain and snow or
even plain rain in the lower valleys which would reduce overall
snowfall totals. Still, any rain is likely to go back over to snow
Sunday evening as a strong cold front moves through the area so
additional snowfall amounts will be possible then in areas that
switch briefly to rain Sunday afternoon.

With the snow levels (and thus snowfall totals) still slightly
uncertain below 5000 feet, the winter storm watches were left as
is for Churchill, Pershing, Mineral, southern Lyon, and Mineral
Counties as most impacts there require snow levels below 5000
feet. For the Reno-Carson City-Minden area, even if snow levels
briefly rise above valley floors along and east of highway
395/I-580, a heavy snowfall is still likely just above valley
floors for significant impacts. Also, the lower valleys will still
see another round of moderate or even heavy snow Sunday evening
with the front. With all this in mind, the winter storm watch was
upgraded to a warning for far western NV starting late Saturday
night. -Snyder

LONG TERM...Monday through Friday...

Snow showers will diminish on Monday, through a few showers may
linger into the early part of Tuesday as moisture and low clouds
may be slow to diminish. By Wednesday, high pressure will return
to the region with light winds. However the high pressure system
will help strong valley inversions develop, which could keep
temperatures colder than normal in the valleys.

Good news for the Sierra, high pressure will return on Wednesday
with a few days of good weather in the Sierra to aid in storm
recovery. Highs should climb well into the 30s with light winds.

Across western Nevada, strength of the inversion will likely be
determined by the snowpack. With a winter storm and widespread snow
possible on the Nevada valley floors forecast for Sunday-Monday,
thinking is valley inversions will be quite strong. This would
leave afternoon highs in the low 30s, with potential for areas of
fog and a lengthy period of poor air quality for the second half
of the week. Brong


Snow will continue across the Sierra tonight with scattered snow
showers for western Nevada. Several inches of additional
accumulation are likely for KTVL and KTRK tonight. For KMMH,
winds may allow shadowing to kick in, so snow could be more

Main event is the Saturday Night into Monday when another lengthy
period of heavy snow will lead to LIFR/IFR conditions in the
Sierra. Strong winds with the jet stream will lead to periods of

Across western Nevada, periods heavy snow should move into the
region by early Sunday morning and persist into Sunday Night or
early Monday morning. More than 6 inches of snow may accumulate on
valley floors, with IFR/LIFR conditions probable. Brong


.REV Watches/Warnings/Advisories...
NV...Winter Storm Watch from late Saturday night through late Sunday
     night NVZ005.

     Winter Storm Warning until 4 AM PST Monday NVZ002.

     Winter Storm Watch from late Saturday night through late Sunday
     night NVZ001-004.

     Winter Storm Warning from midnight Saturday night to 4 AM PST
     Monday NVZ003.

CA...Winter Storm Warning until 4 AM PST Monday CAZ071.

     Winter Storm Watch from late Saturday night through late Sunday
     night CAZ070.

     Winter Storm Warning until 4 AM PST Monday CAZ073.

     Winter Storm Warning until 4 AM PST Monday CAZ072.



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