Winter Storm Warning 6, NWS Reno, NV

Area Forecast Discussion
National Weather Service Reno NV
238 AM PST Mon Dec 26 2022

.SYNOPSIS...

Dry and mild conditions will prevail for one more day with
considerable high clouds. Very strong winds and heavy rain are
expected in the Sierra tonight and Tuesday. Rain will transition
to snow in the Sierra Tuesday afternoon as snow levels drop to
foothill elevations Tuesday night. Additional storms will keep the
chance of rain and mountain snow going with additional impacts
possible through New Years Day.

&&

.SHORT TERM (Through Wednesday)...

Storm Highlights:

* A strong atmospheric river storm is poised to impact the Sierra
  and western Nevada late Monday into early Wednesday morning with
  widespread impacts including: strong and potentially damaging
  winds, heavy rain, and Sierra snow.

* The peak of the wind impacts are expected Monday night into
  Tuesday morning ahead of the precipitation. High Wind Warnings are
  in effect for much of the Sierra, NE California, and W.Nevada.

* The first phase of the storm will have high snow levels with
  about a 12 hour period of moderate-heavy rain in the Sierra
  before snow levels drop to Sierra pass levels Tuesday afternoon.

* Impacts from snow across the Sierra are expected from early
  Tuesday evening into Wednesday morning with heavy/wet Sierra
  cement type snowfall. Winter Storm Watches have been upgraded to
  Warnings across the Sierra and Advisories for NE California.

* For western Nevada, this will largely be a rain and wind event
  with a few inches of snow accumulation possible for foothill areas
  by Wed AM. While some minor urban and poor drainage area flooding
  is likely during periods of high rainfall rates, mainstream river
  flooding is not anticipated but rises are expected.

Storm Details:

* STRONG AND DAMAGING WINDS: High Wind Warnings are currently in
  effect from Monday evening into Tuesday across NE California,
  the eastern Sierra, and portions of western Nevada due the
  potential for high winds ahead of the incoming precipitation.
  Widespread wind gusts in the 50-60 mph range are expected. Wind
  prone locations including foothill areas and along Highway 395
  are looking at about a 70% probability of exceeding 60 mph gusts
  and a 30% chance of exceeding 80 mph. Winds of this magnitude
  can be damaging, so be sure to make preparations ahead of time
  and secure any loose outdoor items or bring them indoors. Expect
  impacts to travel, aviation, as well as downed fences and trees.

* PRECIPITATION (WARM PHASE through Tuesday Afternoon): Being a
  moisture laden atmospheric river storm, snow levels will quickly
  jump from 7500' to near 9000-10000' with the arrival of the main
  moisture surge Tuesday morning. Moderate to heavy rain will be
  widespread across the Sierra with spillover rain pushing into
  western Nevada valleys. Rain amounts during this timeframe will
  generally range from 1.5-2.5 inches across the eastern Sierra.
  Western Nevada spillover rain of 0.50-1.0" is possible with less
  than a quarter of inch expected east of US-95A across the Basin
  and Range. Sierra elevations above 8500' could see 5-10" of
  heavy/wet Sierra cement which could impact higher passes such as
  Mt Rose Summit (SR-431) and Carson Pass (SR-88).

* PRECIPITATION (COLD PHASE Tuesday afternoon into Wednesday): A
  cold front will move through the region and lower snow levels to
  near Sierra pass levels (7000-7500') by early Tuesday afternoon
  and near lake level by early Tuesday evening before dipping to
  around 5000' early Wednesday morning. This will be the period
  where most widespread travel impacts are expected due to
  moderate to heavy snow. Elevations above 7000 feet could see
  12-18" of heavy/wet Sierra cement and up to 2 feet mainly above
  8000', particularly along the Sierra crest. While western Nevada
  valleys will see mainly rain, a rain/snow mix will be possible
  on the valley floor Wednesday morning with foothills potentially
  receiving a slushy few inches of snow.

Fuentes

.LONG TERM (Wednesday Night through New Years Day and Beyond)...

The active pattern is going to continue through New Years Day and
beyond as a moist westerly flow persists across the Pacific with
no blocking pattern to keep shortwaves from reaching the Sierra
and western NV through the first week of January. Latest guidance
indicates these storms will be fairly mild with fluctuating snow
levels, but nothing too extremely high as the main belt of
westerlies will be centered far enough south to allow for our area
to be on the "cooler" side of the jet. This should help mitigate
hydrologic issues while bringing beneficial improvements to higher
elevation snowpack.

Back to this final week... we will have a relative break in the
coverage and intensity of rain/snow Wednesday night into Thursday
morning (including the Wednesday evening/Thursday morning
commutes). The flow is still rather moist such that orographic
lift should keep snow showers going in the Sierra for some light
accumulations. Models had previously been struggling with timing
of upstream energy, but have now honed in on the next several
waves to affect our area late week into the New Years weekend.
Given the flow is fast, there will likely be some timing
adjustments to each subsequent wave. So for the latest...

The first couple of shortwaves will bring light to moderate
precipitation Thursday afternoon through Friday with the first one
late Thursday the colder of the two with snow levels near or just
above western NV valley floors. Some light snow is possible even
down to lowest elevations. Right now, much of the precipitation
will fall during the afternoon Thursday before snow levels then
rise a bit Thursday evening in the wake of the first wave. Impacts
should be confined to the Sierra and foothill locations. Another
fast moving shortwave brings another round of Sierra snow and
valley rain Friday. For both systems, another couple of feet of
snow is likely above 7000 feet with several inches down to lake
level and foothill locations. Even many lower elevations into
western NV should see more beneficial precipitation.

The third system is the most interesting of the three waves as it
digs a bit more, showing signs of splitting as it moves inland.
Latest guidance shows this system holding together long enough to
bring a rather dynamic setup in the moist deformation likely to
extend across the Sierra into western NV Friday night through
Saturday night. QPF is quite robust with WPC guidance indicating
3-4 inches along the crest from Tahoe southward with 1+ inches
along the Hwy 395 corridor between Reno and Mammoth Lakes, and
0.50+" out into the Basin and Range! While there is still some
uncertainty in how far south the third system tracks (how soon
will it split), these numbers could be a bit low based on the
latest track. Saturday could be one of those significant snow days
in the Sierra and foothills with cold rainy conditions for western
NV. Latest NBM indicates a 50% chance of 2+ inches at KMMH and 35%
chance of 1+ inches at KRNO. Given the abundant moisture
associated with this system, the snow character is likely to once
again be a heavy wet one. Stay tuned!

Hohmann

&&

.AVIATION...

...Heightened threat of damaging winds and severe turbulence
late tonight into Tuesday morning...

A strong storm will bring very strong winds tonight and Tuesday
as a 160+ upper level jet pushes into the northern Sierra and
FL100 winds increase to 70-80 kts. Widespread LLWS, rotors and
turbulence are likely tonight through Tuesday afternoon with the
main period to watch being 06Z-18Z Tuesday, along and just ahead
of the main precipitation band. This period has the highest
probability of severe turbulence, strong LLWS, and surface wind
gusts in excess of 50 kts along the eastern Sierra from KSVE-KMMH,
potentially impacting all Sierra and western NV terminals. As
rain spills over into western NV Tuesday morning, surface winds
will drop down a bit, but LLWS will continue to be close to SSW
50-55 kts at FL020 into the early afternoon. If we had to pick a
window for the most extreme wind impacts, current projections
would be as follows:

KSVE: 06-12Z

KTRK,KTVL: 07-13Z

KRNO,KCXP,KMEV: 10-17Z

KMMH: 12-18Z

A period of rain and high elevation snow will follow the strongest
winds, although it will remain quite breezy and turbulent even
into Tuesday night. Most widespread MVFR conditions and terrain
obscurement will be in the Sierra where showers are likely to
persist through much of the week as additional waves move through
the region in a moist westerly flow aloft. If there was to be a
"lull" in the storm pattern this week, latest projections now
indicate a much lighter period of precipitation from midday
Wednesday through Thursday morning.

Hohmann

&&

.REV Watches/Warnings/Advisories...
NV...High Wind Warning from 10 PM this evening to 10 PM PST Tuesday
     NVZ005.

     High Wind Warning from 10 PM this evening to 10 AM PST Tuesday
     NVZ002.

     Winter Storm Warning from 10 AM Tuesday to 10 AM PST Wednesday
     NVZ002.

     High Wind Warning from 10 PM this evening to 10 PM PST Tuesday
     NVZ001.

     High Wind Warning from 10 PM this evening to 10 PM PST Tuesday
     NVZ003.

     Wind Advisory from 10 PM this evening to 10 PM PST Tuesday
     NVZ004.

CA...High Wind Warning from 10 PM this evening to 10 PM PST Tuesday
     CAZ070.

     High Wind Warning from 10 PM this evening to 10 AM PST Tuesday
     CAZ071.

     Winter Weather Advisory from 10 AM Tuesday to 10 AM PST
     Wednesday above 5500 feet for CAZ071.

     High Wind Warning from 10 PM this evening to 10 AM PST Tuesday
     CAZ072.

     Winter Storm Warning from 10 AM Tuesday to 10 AM PST Wednesday
     CAZ072.

     High Wind Warning from 10 PM this evening to 10 AM PST Tuesday
     CAZ073.

     Winter Storm Warning from 10 AM Tuesday to 10 AM PST Wednesday
     CAZ073.

&&