Winter Storm and Heavy Snow in Nevada, December 12 to 15, 2021

Area Forecast Discussion
National Weather Service Reno NV
323 AM PST Sun Dec 12 2021

.SYNOPSIS...

A major winter storm with periods of strong winds, significant
snow in the Sierra, and a mix of rain and snow for western Nevada
remains on track for today through Tuesday. Lengthy travel delays
in the Sierra are nearly certain with full closures also possible.
Another colder winter storm is expected Wednesday into Thursday
with more travel impacts expected.

&&

.SHORT TERM...through Tuesday Night...

The snow has already begun for northeast CA and along the Sierra
crest, and we're still a while before the peak snow intensity
arrives. Travel delays are definite, with outright closures at
times probable for the Sierra when the snowfall intensity ramps
up this evening to a consistent 1-2"/hour rate, and then could
reach or exceed 3"/hour for a few hours Monday late afternoon-
evening. Any non-emergency travel is not recommended in the Sierra
through at least Tuesday. Check in with our partners at NDOT,
CalTrans, CHP, and NHP for road conditions information.

While some light rain and snow (higher foothills) showers will
reach into eastern Lassen County and far western Nevada this
morning, these areas will likely be largely shadowed out until the
bulk of the precipitation spills over from early Monday morning
into Tuesday. Periods of gusty to strong winds will also accompany
this storm, with the best chance in northeast CA, northwest and
far western NV today, then shifting to areas south of US-50 for
Monday.

While the storm will begin to wind down by late Tuesday, digging
out after the storm may keep travel impacted into Wednesday,
especially with temperatures becoming quite chilly Tuesday night
from the widespread new snow cover. Then, there is another
winter storm following right on its heels Wednesday afternoon into
Thursday (see long term section for more details).

Here are the highlights:

* SNOW:

Snow totals will be measured in feet (and even yards!) in the
Sierra and could easily surpass a foot for higher elevations
(5500+ feet) in western Nevada, with several inches down to valley
floors. See our latest Winter Weather Messages for more details on
potential snow amounts.

With this amount of snow, avalanches certainly become a concern
for the mountain areas. The Sierra Avalanche Center has issued an
avalanche watch for this evening into Wednesday for backcountry
areas from Yuba Pass to Ebbetts Pass (next update by mid morning);
refer to the Eastern Sierra Avalanche Center for the latest
guidance on backcountry avalanche conditions in Mono County.

As far as snow "down here" in western NV valleys, timing
considerations for snow levels bring quite the range of
possibilities below 5000 feet, with 1 to 3" virtually certain,
and a "most likely" scenario of 3-8" late Monday evening into
Tuesday. The foothills above 5500 feet, however, are going to be
predominately snow. At least 5-10" of snowfall are expected, with
10-20" (and up to 2 feet possible) for higher locations including
Virginia City and the Virginia Highlands. Anticipate large ranges
in snow totals between elevations in the 5000-5500 feet range;
however, there is a high probability of at least 3-8" as the
changeover from soaking rain to heavy snow begins Monday evening.
A few rumbles of thunder could also occur within the most intense
snow bands from late Monday afternoon/evening for parts of
northeast CA, the Tahoe region and the far western NV cities, and
into the late night for western Mono County.

* SNOW LEVELS:

The biggest question mark with snow levels are for areas below
5500-6000 feet. Most areas above 6000 feet should stay as snow
for the entire event. While valleys could go back and forth
between rain and snow through the event, there is high confidence
in a full transition to snow with the cold front Monday evening
into Tuesday morning, and there is a hint of a slightly earlier
changeover resulting in an upward trend for snowfall in the lower
elevations. While the West Central NV Basin and Range aren't
included in any winter storm watch or warning, they are still in
line for meaningful accumulations of 1-4" late Monday night into
Tuesday, where snow levels will take somewhat longer to drop for
the Lovelock-Fallon areas and other locations below 4000 feet.
For all valley locations, prepare for periods of slower travel
with the rain Monday, and in particular both commutes on Tuesday
when snow and colder temperatures will lead to slick and icy
spots even after the main snow ends.

* LIQUID TOTALS:

The main change made was pushing liquid totals higher for the
Reno-Carson City-Minden corridor. Ensemble guidance is trending
upward and 2" total precip (rain + snow water equivalent) is
looking like a reachable target for the urban areas, with greater
amounts for western foothills. Farther east into west central NV,
totals between 0.50-1.0" are likely from this storm, with
localized higher amounts.

The colder nature of this storm means little to no chance for
river flooding and the ensemble RFC guidance reflects this.
However, urban ponding of water from poor drainage can be expected
in the lower valleys due to moderate-heavy rain Monday before the
transition to snow.

* WIND:

700-mb winds remain impressive, with 45-55 kts in forecast
simulations. This is plenty of wind energy aloft but with heavier
precipitation rates the stronger winds are more likely to be
damped out. We'll continue to watch wind prone locations along the
Sierra Front today through this evening (currently in a wind
advisory, with some strong gusts of 55-65 mph already reported
along the US-395/I-580 wind prone sites), then the wind risk
shifts south of US-50 for Monday and Monday night. The areas that
stand out currently are wind prone locations along the US-395
corridor in the Eastern Sierra and US-95 near Walker
Lake/Hawthorne before the precipitation arrives. There is an 80%
chance for seeing max wind gusts exceed 60 mph in these areas
during that time frame. For other locations, seemingly random
strong wind gusts may periodically surface if precipitation rates
slow. Sierra ridges are expected to see winds gusting over 100 mph
at times leading to near white-out conditions along with the
snow. MJD

.LONG TERM...Wednesday through the end of next week...

* Rundown: A short break will occur between winter storms late
  Tuesday night into Wednesday morning before another notable,
  although not as intense, winter storm brings more snow to the
  mountains and valleys. This brief period will be a good time to
  clear snow and gather supplies before the next storm begins
  Wednesday afternoon and evening. Now into the details.

* The details: Another period of travel impacts is expected
  Wednesday afternoon into Thursday morning for the Sierra, and
  Wednesday evening into Thursday morning for the lower valleys of
  western Nevada. Due to the cold nature of this system, an
  additional 1-2 feet of snow are possible in the Sierra, with
  several inches possible down to valley floors in western Nevada.
  There is still low-end uncertainty with how cold this system
  will be, with 20% of the ensemble clusters continuing to trend
  slightly warmer with this system as the base of the upper-level
  trough stays farther north. Even with this slight uncertainty,
  forecast confidence remains moderate in the previously stated
  scenario. Friday may be the first good travel day of the week.

* Extended forecast: Beyond next week, the synoptic pattern
  continues to look active. We should likely be above normal with
  regards to precipitation, and leaning slightly below normal
  temperature-wise.

-Johnston

&&

.AVIATION...

A major winter storm will impact the region beginning very late
tonight and lasting through Tuesday. Significant impacts to
aviation are expected. Check with your airlines for flight delays
or cancellations due to this prolonged period of hazardous
weather conditions.

Wind/LLWS Potential:

* Gusty southerly winds will increase today. The potential for
  mountain wave turbulence and LLWS increases this afternoon into
  Sunday as the storm moves into California. Surface gusts should
  remain below 40 kts for most terminals, with a 20-30% chance of
  gusts exceeding 50 kts at TRK-TVL-CXP-RNO. Southerly winds enhance
  the threat for LLWS at KRNO.

* Gusty winds with widespread turbulence and LLWS potential will
  continue into Monday with the strongest gusts likely shifting
  south and eastward to west central NV. However, any of the
  terminals could see bursts of stronger gusts of 40-50+ knots
  with the approaching cold front during the afternoon-evening.

Snow Potential:

* TRK-TVL: Snow will begin early this morning, with the heaviest
  snow forecast for Monday into Tuesday. Accumulations will likely
  exceed 2 feet, with nearly continuous IFR/LIFR conditions
  expected through Tuesday morning.

* RNO-CXP-MEV: The highest probability for continuous rain will
  begin Monday morning and continue into early Tuesday morning,
  ending as snow in all areas. Snow should begin accumulating
  Monday night at these terminals as snow levels drop to valley
  floors. Accumulations will likely exceed 2 inches, with CXP-MEV
  having an 60-75% chance of exceeding 4 inches. RNO has a 50%
  chance of exceeding 4 inches.

* MMH: Snow begins later this evening, with heavy snow and long
  duration IFR/LIFR conditions expected Monday into Tuesday.
  Accumulations will likely exceed 1 foot, with a 50% chance of
  exceeding 2 feet.

Another storm is possible midday Wednesday lasting possibly into
Thursday evening. The Sierra will likely see another round of heavy
snow and western NV may see several inches of snowfall. MJD

&&

.REV Watches/Warnings/Advisories...
NV...Lake Wind Advisory from 10 AM this morning to 5 PM PST this
     afternoon for Pyramid Lake in NVZ004.

     Winter Storm Watch from Monday evening through Tuesday evening
     NVZ001.

     Winter Storm Warning until 10 PM PST Tuesday NVZ002.

     Wind Advisory until 10 PM PST this evening NVZ003.

     Winter Storm Watch from Monday afternoon through Tuesday morning
     NVZ005.

     Winter Storm Watch from Monday evening through Tuesday afternoon
     NVZ003.

CA...Winter Storm Warning until 10 PM PST Tuesday CAZ072.

     Winter Storm Warning until 4 PM PST Tuesday CAZ071.

     Winter Storm Watch from Monday afternoon through Tuesday morning
     CAZ070.

     Winter Storm Warning from 10 PM this evening to 10 PM PST
     Tuesday CAZ073.

&&

For more information from the National Weather Service visit...
http://weather.gov/reno