Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 132226

Area Forecast Discussion
National Weather Service Reno NV
326 PM PDT Tue Mar 13 2018


The first in a series of storms will bring gusty winds, rain and
snow through early Wednesday, with another round of light to
moderate snow in the Sierra Wednesday afternoon and evening. A
stronger and colder storm then evening into Saturday, producing
additional periods of heavy snow in the Sierra with some snow
accumulation also possible for lower elevations.



The region remains on the warm side of the storm, with
temperatures reaching 70 degrees in parts of west central NV,
Gusty winds around 40 mph have been reported in parts of western
NV, with Yerington reporting visibility between 1/4 and 1/2 mile.
A few lightning strikes have also occurred in Churchill and
Pershing counties. In the Sierra, snow levels are still near 8000
feet but this will change later today as colder air catches up
with the moisture plume. Highlights for this storm through
Wednesday night:

Snow levels...Dropping to pass levels from Tahoe northward
(7000-8000 feet) between 3 and 5 pm, then lowering further to
5500-6000 feet between 6 and 8 pm. For Mono County, snow level
drops will occur later--down to 7000-7500 feet during the
evening, then dropping to near 6000 feet after midnight. For
western NV, the most notable drop in snow levels is expected
between midnight and 4 am, down to 4500-5000 feet. Through
Wednesday, the snow levels will remain between 4500-5000 feet on
average, except near 4000 feet for northeast CA/far northwest NV.

Precipitation/Snow amounts...The heaviest period of accumulation
will begin this evening and continue through the overnight hours
resulting in slick conditions, low visibility, and general
difficult travel conditions around the Sierra. See our latest
Winter Weather Messages associated with the Warning and Advisory
headlines for projected snowfall totals through Wednesday morning.

Snow accumulations for western Nevada will be limited generally to
areas above 5000-5500 feet, with a slushy inch or two possible.
For lower valleys, snow may mix with the rain but accumulations
are not expected on roads as temperatures remain above freezing.
The best advice is to plan for additional time to travel Wednesday
morning, even in areas where wet roads are expected.

A secondary wave will move through the Sierra Wednesday afternoon
and evening, with the best snow potential leaning toward Mono
County. We extended the Winter Weather Advisory in this area
through Wednesday evening, with potential for another 2-6 inches
west of US-395 and 10" near the crest. For Tahoe, lesser
additional snow amounts are projected as the bulk of the snow is
more likely to occur during the daytime then shifting south during
the evening. Elsewhere, scattered snow showers are possible, with
only spotty light accumulations in lower elevations. The only
possible exception may be in higher elevations east of US-95 where
a more organized band of precip could set up Wednesday evening.

Thunderstorms...Isolated convection has already occurred in
Pershing and Churchill counties, with outflow gusts up to 55 mph.
Fast moving cells with a few lightning strikes remain possible in
these areas through 8 PM. Another round of convection is possible
Wednesday afternoon/early evening as the cold core of the upper
low settles over the Sierra and western Nevada, with best
instability north of Interstate 80. MJD

.LONG TERM...Thursday through Tuesday...

High confidence now in a significant storm for late Thursday through
Friday night, especially in the Sierra and NE California. The
GFS/EC/NAM are in very good agreement with the jet location and the
core of the upper low. Leaning more in the GFS/EC precip though as
the NAM shows too much shadowing for this pattern. (A similar, but
shorter, heavy snow pattern to 2004/05 which the NAM did poorly on.)
Ingredients are there for periods of heavy snow, even into Western
NV at times with exit region of jet over I-80, frontogenetical
forcing and instability.

Snow will begin in NE California and the Tahoe Basin Thursday
afternoon then spread south and east overnight. Snow will continue
in NE California through most of Friday and be heavy at times, up to
2" per hour. Amounts of 2+ feet are likely above 7000 feet in the
Tahoe Basin and 1-2 feet in Western Lassen/Eastern Plumas Counties.
With good spillover there too, 6-12" of snow along the 395 corridor
in Lassen County looks likely. Therefore, with the high confidence,
upgraded the Watch to a Winter Storm Warning for Tahoe/Lassen/Plumas.

Farther south into Mono County, the storm will take its time and
looks more like a Friday/Friday night system. The models do show
it weakening slightly as it gets there, but snow still looks good.
Amounts may not be quite as high as areas to the north, although
this could be an artifact of the models` dry bias near Mammoth
Lakes. Will leave the Watch alone here for now, but it will likely
be upgraded in the near future.

For Western Nevada, the heaviest snow is most likely along the 395
corridor. Lighter amounts are likely farther north and east. The
main issue here is the time of year, and timing of the heaviest
snow. In March, peak accumulating snow time is 03-16Z, and the
heaviest snow looks to be 10-20Z. While we see a portion of the
heaviest snow during this time, accumulations could be a bit
reduced in the valleys due to stronger insolation after 16Z. The
Watch looks good, with several inches still looking possible on
the valley floors and 12" or more possible in the foothills and
around Virginia City. For areas farther north and east,
advisories may be needed for Northern Washoe and the Highway 95
corridors Friday morning with up to 4" of snow.

The core of the upper low then moves overhead Saturday with the
threat of showers and isolated thunderstorms as the models
remain in good agreement. Then we get a bit of a break Sunday
into Monday under short wave ridging. Then another cutoff low
develops near 140W and slowly progresses inland next Tuesday into
Thursday. Another period of wet weather looks likely, but exact
timing, snow levels and amounts remain nebulous. X



Multiple impacts to aviation through Wednesday night--for the
Sierra terminals, IFR/LIFR conditions this evening thru early Wed
AM, with several inches of snow accumulation. Secondary wave could
bring more IFR conditions and a few more inches of snow Wednesday
afternoon and evening with best chances at KMMH.

For lower elevation terminals, rain will bring MVFR conditions
with brief IFR possible in heavier showers through early evening,
and again late tonight with snow possibly mixing in between

Wind gusts of 35-40 kt and locally higher gusts associated with
convective shower bands will continue into this evening, with the
stronger winds easing off after 03Z.

Isolated thunderstorms could continue through 03Z for west
central NV, and are again possible Wednesday from 21Z-03Z mainly
north of Interstate 80--unlikely to affect the main terminals
but could affect flight paths east of KRNO.

After a short break late Wednesday night and Thursday, a stronger
and colder storm will bring another round of heavy snow for the
Sierra terminals, with snow also possible at times for KRNO/KCXP
Thursday night through at least Friday. MJD


.REV Watches/Warnings/Advisories...
NV...Wind Advisory until 7 PM PDT this evening NVZ005.

     Winter Storm Watch from Thursday afternoon through late Friday
     night NVZ003.

     Winter Storm Warning until 11 AM PDT Wednesday NVZ002.

     Winter Storm Warning from 5 PM Thursday to 5 AM PDT Saturday

     Lake Wind Advisory until 7 PM PDT this evening for Pyramid Lake
     in NVZ004.

CA...Winter Weather Advisory until 11 AM PDT Wednesday CAZ071.

     Winter Storm Warning from 2 PM Thursday to 11 PM PDT Friday

     Wind Advisory until 7 PM PDT this evening CAZ070.

     Winter Weather Advisory until 1 AM PDT Thursday CAZ073.

     Winter Storm Watch from Thursday afternoon through late Friday
     night CAZ073.

     Winter Storm Warning until 11 AM PDT Wednesday CAZ072.

     Winter Storm Warning from 5 PM Thursday to 5 AM PDT Saturday



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