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000
FXUS65 KREV 242155
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
255 PM PDT Fri Mar 24 2023

.SYNOPSIS...

A stubborn upper-level trough will continue to bring below-seasonal
average temperatures and snow showers across the region through the
weekend. Another impactful winter storm is slated for later Monday
night through Wednesday, with strong winds, heavy Sierra snowfall,
and valley rain or snow possible.

&&

.DISCUSSION...

Today through the Weekend:

* Colder Temperatures: A surge of cold air ushered in by the cold
  front this morning can surely be felt out there today. A broad
  long-wave trough centered over the Great Basin will continue to
  bring chilly conditions and chances for snow showers Saturday
  and Sunday. Temperatures will remain 15-20 degrees below normal
  for late March, with daytime highs in the low 40s for western
  Nevada and lower 30s for Sierra Nevada communities. Overnight
  lows will reflect the much colder than average temperatures,
  dropping into the low 20s across most western Nevada valleys,
  and even single digits for colder Sierra valleys. Make sure to
  stay warm!

* Chances for Snow Showers: Diurnal heating beneath transient short-
  wave troughs pivoting around the broad long-wave trough will
  provide low-mid level instability to generate hit-or-miss snow
  showers area wide each afternoon Saturday and Sunday.
  Precipitation will be light, with less than a few hundredths of an
  inch with higher elevations seeing snow accumulations of less than
  an inch.

A Small Break Monday:

* Monday will be a transition day leading to the next stronger
  storm affecting the region Monday night through Wednesday. Warm
  air advection associated with a short-wave ridge ahead of this
  winter storm will warm temperatures a little bit Monday;
  although, this will not feel like that much of a warm-up as
  daytime highs will still be around 10-15 degrees below average
  (average for this date is 61 degrees at Reno). Cloud cover and
  south-southeast winds will increase throughout the day.

Impactful Winter Storm Monday night through Wednesday:

Storm Changes:

* We have issued a Winter Storm Watch for northeast California, the
  Lake Tahoe Basin, and the Eastern Sierra Monday evening into
  Wednesday afternoon due to increasing confidence in an impactful
  winter storm affecting these areas.

* Medium-range deterministic and ensemble guidance show rapid
  surface cyclogenesis occurring a few hundred miles off the
  southern Oregon/northern California coast Monday afternoon and
  evening as two areas of low pressure merge, one moving equatorward
  from the Gulf of Alaska, and another moving east over the Eastern
  Pacific Ocean. This throws a wrench into the forecast, as this
  rapid cyclogenesis and the subsequent changing isallobaric wind
  gradient could vary the position of the surface low and,
  consequently, the trajectory of the Pacific-sourced moisture plume
  as it pushes into the Sierra Nevada. Depending on where the
  surface low makes landfall will generate a potential boom-bust
  scenario for snowfall across the region. More on this below.

Storm Details:

* Winds: Current ensemble guidance directs the surface low into
  the northern California coast, which generates meridional flow
  and southerly winds across the region. Winds will increase
  Monday night into Tuesday, with gusts up to 40 mph possible for
  the lower valleys of northeast California and far northwest
  Nevada, with 40-50 mph gusts possible across western Nevada and
  the Basin and Range, and 35-45 mph gusts for the valleys of the
  Sierra Nevada. Ridgetop winds near the Sierra Nevada crest will
  likely gust over 100 mph.

* QPF/Snowfall: The most widespread precipitation is likely within
  a 12-18 hour window Monday night into Tuesday. Forecaster
  confidence is currently low-medium regarding precipitation
  amounts at this time. A boom-bust scenario exists, depending on
  how far north or south the surface low makes landfall. The
  "bust" scenario with a 25% probability - If the low tracks more
  south compared to the current forecast, an upper-level dry air
  intrusion could push into the Sierra Nevada, which would quickly
  taper off precipitation from north to south. The "boom" scenario
  with a 20% probability - If the low tracks closer to the north-
  central Sierra Nevada, strong mid-level frontogenesis could
  generate heavy-banded snow and higher-end snow totals. Due to
  these varying scenarios, a large spread in QPF and snowfall
  amounts exists within the probabilistic guidance. We have taken
  the middle ground with the forecast. QPF projections for this
  storm along the Sierra Nevada crest are around 2.50". With this
  storm being on the colder side with snow-to-liquid ratios around
  12:1 to 15:1, this could translate into 2-3 feet of snowfall
  along the Sierra crest, with 10-20" for the Lake Tahoe Basin,
  around Mammoth Lakes, and mountainous areas of northeast
  California west of US-395. Snow totals on the valley floors of
  western Nevada could reach up to 2", with 2-6" possible for
  foothill locations and Virginia City. However, the late March
  insolation will probably limit the amount of accumulation on
  paved surfaces.

* Impacts: Heavy snowfall could exacerbate the ongoing snow load
  concerns, especially if the "boom" scenario pans out. Due to the
  higher snow-to-liquid ratios, gusty winds may also bring areas
  of blowing and drifting snow, which would further reduce
  visibility and bring significant travel difficulties across the
  Sierra Nevada. Periods of stronger winds Monday night into
  Tuesday will pose a threat to aviation interests, high-profile
  vehicles, and recreation. Use this quiet period through Monday
  morning to prepare for this winter storm.

Later Next Week:

* North-to-northwest flow aloft looks to keep temperatures well
  below average, with weak shortwave passages bringing chances for
  light snow showers. There is the potential for slight ridging
  over the Eastern Pacific near the latitude of the northern
  California coast, which would direct the storm track more into
  the Pacific Northwest, leaving us with fewer chances for heavier
  precipitation (hopefully).

-Johnston

&&

.AVIATION...

* Generally VFR conditions through Sunday outside isolated snow
  showers north of I-80 and along the Sierra each afternoon and
  evening. Brief accumulations up to 1/2 inch are possible at KTRK-
  KTVL with little or no accumulation at other terminals. Breezy
  west-northwest winds will develop each afternoon/evening across
  the ridges and over western NV, gusts generally peaking around 20-
  25 kts through this evening and again Saturday, then about 5 kts
  lighter for Sunday.

* Our next winter storm approaches Monday and moves through the
  Sierra and western NV Monday night through Wednesday. The worst
  conditions will occur late Monday night into Tuesday evening as
  the front and most intense band of wind and snow move through the
  region from north to south. Prepare for widespread turbulence/LLWS
  and heavy snow throughout the Sierra during this time frame. Snow
  levels will fall to all valley floors, so some light accumulating
  snow cannot be ruled out by late Tuesday afternoon/evening. As the
  front exits to the south, winds will lessen late Tuesday night and
  Wednesday. However, it will remain unstable with scattered snow
  showers, especially in Sierra locations.

Hohmann

&&

.AVALANCHE...

* We will see overall quieter conditions Saturday and Sunday, with a
  few brief snow showers producing minimal additional accumulations
  (up to an inch in the heavier showers).

* A Winter Storm Watch is in effect from Monday evening through
  Wednesday afternoon for the Lake Tahoe Basin, and Monday night
  through Wednesday afternoon for Mono County. This impactful storm
  looks to bring additional SWE amounts of 2-3". With this system on
  the colder side, snow-to-liquid ratios of 12:1 to 15:1 are
  possible. At this time, 2-3 feet of snow is possible along the
  Sierra Nevada crest, with 1-2 feet for areas above 8000 feet. High
  winds may also produce blowing and drifting snow.

-Johnston

&&

.REV Watches/Warnings/Advisories...
NV...Winter Storm Watch from Monday evening through Wednesday
     afternoon NVZ002.

CA...Winter Storm Watch from Monday evening through Wednesday
     afternoon CAZ071-072.

     Winter Storm Watch from late Monday night through Wednesday
     afternoon CAZ073.

&&

$$