Heavy Snow in Nevada, January 4 to 5, 2023

Area Forecast Discussion
National Weather Service Reno NV
500 AM PST Wed Jan 4 2023

.UPDATE...

Quick update this morning to issue a Lake Wind Advisory for
Pyramid Lake this afternoon through Thursday morning.

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.PREVIOUS DISCUSSION... /issued 224 AM PST Wed Jan 4 2023/

SYNOPSIS...

Our active weather pattern continues to keep storms lined up for
the upcoming week, so remain prepared for winter driving
conditions. A period of accumulating snow moves through this
morning, then after a short break later today, another round of
rain and snow returns late tonight and Thursday. Additional potent
storms are expected this weekend and early next week.

DISCUSSION...

Here comes the next storm, which will feature a few phases as it
makes its way across the region today through Thursday:

* MORNING SNOW: This morning will quickly transition from dry to
  snow as a wave of moisture ahead of the next storm advances
  rapidly from the southwest. Warm advection processes and broad
  upper divergence will efficiently spread a band of snow across
  the Sierra and western NV from around daybreak through midday.
  High resolution models are about 2 hours earlier with the onset
  of snow (by 5 or 6 AM) than the standard resolution guidance,
  which would have a greater impact on the AM commute across the
  urban areas. All advisories and warnings look on track with the
  projected snow amounts, although we could start to accumulate
  snow an hour or two earlier if faster timing of the high-
  resolution guidance verifies.

* WARM SECTOR WITH WINDS THIS AFTERNOON-EVENING: After this
  morning's snow area exits to the north, southeast to south winds
  will increase and push snow levels much higher this afternoon
  and evening to near 7500 feet in the Sierra and 6000-7000 feet
  for much of western NV/northeast CA. Also during this time,
  precipitation will become much more spotty, with isolated
  showers mainly near the Sierra crest and well north of I-80.
  Wind gusts will increase to 30-40 mph in most lower elevations
  by late afternoon and continue through tonight, although some
  high resolution guidance indicates that enhanced gusts of 50-65
  mph could push through Mineral/southern Lyon counties this
  evening through early Thursday morning and affect the wind-prone
  US-95 corridor, so we will add a Wind Advisory for this area.
  Sierra ridge gusts are expected to peak in the 100-120 mph
  range.

* COLD FRONT WITH PRECIP LATE TONIGHT-THURSDAY AM: Precip becomes
  more organized and heavier along the Sierra by late evening
  through Thursday morning, when the bulk of the heavy snow
  accumulations are likely to occur. Meanwhile, shadowing keeps
  precip rather sparse for most lower elevations except from
  around 4-10 AM with the cold front passage. With the main upper
  low remaining well offshore, the air mass behind this front
  won't be cold enough to push snow levels all the way back down
  to the lower valleys. Away from the Sierra, most of the precip
  looks to be as rain, with maybe an inch or two of snow above
  5000-5500 feet, and brief rain-snow mix possible below 5000 feet
  right along the front.

From Thursday afternoon-evening, a trailing shortwave keeps bands
of snow showers going for the Sierra with several more inches of
snowfall for the Tahoe basin southward to western Mineral county,
and up to 1 foot near the crest, with lighter rain and snow
showers occasionally pushing into lower elevations. By the time
snow levels finally drop below 5000 feet late Thursday night in
western NV, the precip event will essentially be done.

For Friday, a short break in the storm action looks more likely.
While we can't rule out a weak shortwave bringing isolated
showers to the Sierra or northeast CA, impactful amounts of snow
or rain aren't expected, so this may be the best day to travel
over the Sierra before the next storm comes in over the weekend.

This Saturday-Sunday storm is looking to be a medium-intensity
system with about a 6-12 hour period of heavier snow for the
Sierra and a shorter round of snow down to most valleys most
likely from Saturday night into Sunday morning. Early snowfall
projections indicate about 6-12" for eastern CA west of US-395
including the Tahoe basin, 1-2 feet above 7000 feet near the
Sierra crest, and a few inches for the main urban areas of far
western NV. However, the Pacific moisture tap may persist through
Sunday and increase the snowfall total further for parts of the
Sierra.

For next week, a more intense and moisture-rich storm is still
likely for the Monday-Tuesday time frame. There are a lot of
complexities with this system in terms of varying snow levels,
wind gust potential, and location/duration of heaviest precip. The
impacts will also cover a wide range of possibilities from major
winter travel hazards to rapid rises on rivers and creeks and
potential flooding. Our current projection of liquid precip
amounts several days in advance (subject to change) mentions 1-2"
for the main urban areas of far western NV, dropping off farther
east to about 0.25-0.50" for US-95 communities, 2-5" for
northeast CA, Tahoe basin southward to western Mono County, and
5-7" along the Sierra crest from the Sunday night through Tuesday
night time frame. Keep extra attention to our forecasts for this
time frame and it's never too early to consider alternative travel
plans to avoid the days with the most significant impacts. MJD

AVIATION...

* Pockets of FZFG and low stratus are in place early this morning
  with the most likely to impact W NV terminals, including KRNO,
  KCXP, KMEV, and KNFL. This will bring terrain obscuration to
  portions of W NV and NE CA as well as around Mono Lake.

* Snow moves into the Sierra/NE CA/W NV around daybreak today,
  courtesy of our warm front lifting through the region. There
  will be a brief break, or at least lighter showers this
  afternoon and evening before the cold front shifts through
  overnight into Thursday bringing renewed rain and snow impacts.
  W NV will see a solid break from roughly 22z-08z, with the main
  spillover period of concern from the cold front ~12z-18z.

* All terminal sites will see a mix of rain and snow with this
  event as snow levels fluctuate. Up to 2 inches of snow
  accumulation are possible for western NV terminals (west of
  US-95) this morning before mixing with or becoming rain for the
  remainder of the storm. Sierra terminals will start with snow,
  turn to rain or a rain/snow mix this afternoon, then return to
  all snow again tonight. KTRK/KTVL could see 12-18 inches of snow
  accumulation between this morning and Thursday night with 15-20
  inches at KMMH.

* Winds aloft are beginning to increase early this morning, and
  will strengthen through the day. FL100 winds will be sustained
  45-65 kts through Thursday, starting more SSE and turning toward
  the SW Thursday with the cold front. Mountain wave activity
  will be a bit more limited over the Sierra with the southerly
  flow, increasing as winds turn toward the SW. Turbulence is
  certain. Winds will not mix down to lower valleys initially as
  strong inversions are in place, leading to a wind shear layer.
  Stronger winds will begin to surface for Sierra valleys this
  morning, then into W NV valleys this afternoon. Terminal sites
  will generally see peak gusts around 30 kts, however there is a
  10% chance to exceed 40 kts. The one exception will be for KHTH
  where there is a 70% chance for gusts to reach 45+ kts.

* Flying conditions will improve on Friday, but another storm is
  quick to move in Friday night into Saturday with additional
  waves of moisture the remainder of the weekend and a stronger
  atmospheric river storm from early-mid next week.

-Dawn

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.REV Watches/Warnings/Advisories...
NV...Winter Storm Warning until 4 AM PST Friday NVZ002.

     Wind Advisory from 1 PM this afternoon to 10 AM PST Thursday
     NVZ001.

     Winter Weather Advisory until 4 PM PST this afternoon NVZ003-005.

     Lake Wind Advisory from 1 PM this afternoon to 10 AM PST
     Thursday for Pyramid Lake in NVZ004.

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

     Winter Storm Warning until 4 AM PST Friday CAZ072.

     Winter Storm Warning until 4 AM PST Friday CAZ073.

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