Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 211216
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
416 AM PST Sat Jan 21 2017

.SYNOPSIS...

A relative lull in snow amounts for the Sierra and a break for most
of western Nevada expected today. A very strong winter storm will
impact the region tonight 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.

&&

.SHORT TERM...

MAIN WEATHER CONCERNS TONIGHT INTO MONDAY MORNING:

*A relative lull today with light to moderate Sierra snow showers
 continuing.

*Powerful Winter Storm to impact the Sierra beginning tonight into
Sunday with multiple feet of snow and periods of blizzard conditions.

*This Winter Storm will provide widespread heavy snowfall totals
which haven`t been seen for several years for western Nevada valleys.

*Below are some of the concerns, impacts, and preparation measures
you can take for the Sun-Mon storm.

______________________________________________________________
 WHAT CAN YOU DO:
* For communities in the higher terrain: Tahoe Basin, Mono County
  (looking at you Mammoth), 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.

______________________________________________________________

Today (The relative lull in the weather):

Continuous light to moderate snowfall will persist through the day
today across the Sierra with only very light spillover showers
expected across western Nevada. Slow and hazardous travel in the
Sierra, chain controls, and period of road closures have been
occurring over in the last 24 hours but if you need to travel this
is the relative lull in the weather before conditions really take a
turn for the worse ahead of a strong winter storm that will impact
the region tonight. After midnight, conditions may make travel
impossible. Across western Nevada, little additional snowfall is
expected and travel problems should remain with the current snow
and ice on the ground.


Tonight into Monday Morning (Strong Winter Storm): The heavy
snowfall with this storm will come through the area in two waves.

The First Wave: (Approx midnight Sunday to early Sunday afternoon):
This first push is associated with warm air advection and wind
forcing that will produce copious spillover all the way into SW
Idaho and far western Utah. As the main push of moisture comes
through the Sierra it will easily push across the Sierra with little
impediment providing a similar start time for snowfall in western
Nevada as compared to the Sierra.

Do feel nearly all models are shadowing far too much in the valleys
in terms of QPF amounts and as a result have boosted snowfall
amounts through Carson Range foothill areas, and roughly the Hwy 395
corridor through the North Valleys, Reno, and extending south
through the Carson Valley. Higher snowfall amounts are expected
roughly from Washoe Valley through Carson Valley as wind orientation
and distance from the terrain will favor even better spillover. See
the Winter Storm Warning for details on snow amounts.

Farther east towards the western Nevada Basin and Range
accumulating snowfall is likely and have upgraded the Winter
Storm Watch to a Winter Storm Warning for areas such as Pershing,
Churchill, and Mineral Counties. It is likely that the snow levels
will rise a bit during the afternoon Sunday so some valleys below
4,000 feet could see rain begin to mix in with snow by late
morning and then turn back to snow late Sunday afternoon and early
evening.

The Second Wave: (Late Sunday afternoon into Monday morning): This
portion of the storm will be post-frontal meaning a colder air mass
and higher ratio snows can be expected. This too will provide good
spillover for western Nevada but will be more wind and instability
driven versus warm air advection driven. Although strong and gusty
winds are expected Sunday morning, the main window for blowing snow
issues may be toward Sunday late afternoon and evening as snow
becomes lighter/fluffier and blows around easier, even with the wind
lightening through the evening.  Snow will start to diminish by
early Monday morning and really taper off by early afternoon across
the Tahoe Basin and western Nevada with areas in Mono County hanging
on until early afternoon.

Overall, conditions will really go downhill tonight and Sunday so
its best to avoid any travel if possible in the Sierra and across
far western Nevada. Seeing the potential for widespread snow like
this in western Nevada has not occurred for several years. As a bit
of climatology, the chance of seeing snow amounts >10" at the Reno
airport when it does snow are generally less than 1% for any given
winter, but this storm has a good mix of cold air and moisture to
provide it. Some analogs can be made to the copious snow producer in
January of 2005 which produced 1-2` of snow in the valleys but that
storm had some differences and perhaps an even better setup for
spillover and cold air. Overall it will be an interesting storm to
see unfold. Fuentes

.LONG TERM...Tuesday through Saturday...

With broad cyclonic flow and a cold air mass aloft over the region
on Tuesday, light isolated snow showers may continue, but any
additional accumulation will be minimal. By Tuesday night into
Wednesday, the system exits the region with dry conditions likely
the remainder of the week. With light winds and plenty of cold air
trapped in valleys, inversions are expected to develop from midweek
onward. Freezing fog and stratus are definite possibilities in
valley locations, but we will need to see how the snow event Sunday
into Monday plays out first to determine the extent.

The one caveat to the dry forecast is a weak wave dropping down the
California coast the end of the week. The wave doesn`t have much
moisture associated with it, but with plenty low level moisture in
place from the snow, it could result in snow flurries. Ridge builds
into the west for the weekend with a 1044 mb surface high building
across the Great Basin, resulting in easterly flow and strengthening
the inversions. Expect poor mixing and particulate build-up in the
lower valleys with possible reductions to air quality.

The good news for those trying to dig out of the incredible amount
of snow that had fallen this month is that the long range forecast
keeps the area dry through the first week of February. -Dawn

&&

.AVIATION...

Snow showers continue in the Sierra with several inches of
additional accumulation likely for Sierra terminals. Western Nevada
remains largely shadowed today, though a few stray showers may pass
through the area. Main concerns today will be periods of IFR
conditions in the Sierra in addition to widespread mountain
obscuration throughout the Sierra and western Nevada.

Main event is the Saturday Night into Monday when a significant
winter storm moves into the Sierra. Very heavy snow is expected with
15 to 30 inches of accumulation for Sierra terminals and widespread
LIFR/IFR conditions. Across western Nevada, periods heavy snow
should move into the region by early Sunday morning and persist into
Sunday Night or early Monday morning. 8 to 12 inches of accumulation
is possible for KRNO with 12 to 16 inches for KCXP.

With a strong jet directly over the region, turbulence is likely.
With winds ramping up aloft and not fully mixing down to lower
valleys, LLWS is expected Saturday night into Sunday across all
areas. -Dawn

&&


.REV Watches/Warnings/Advisories...
NV...Winter Storm Warning from midnight tonight to 4 AM PST Monday
     NVZ005.

     Winter Storm Warning until 4 AM PST Monday NVZ002.

     Winter Storm Warning from 4 AM Sunday to 4 AM PST Monday
     NVZ001-004.

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

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

     Winter Storm Warning from midnight tonight to 4 AM PST Monday
     CAZ070.

     Winter Storm Warning until 4 AM PST Monday CAZ073.

     Winter Storm Warning until 4 AM PST Monday CAZ072.

&&

$$

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


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