Area Forecast Discussion
Issued by NWS Reno, NV

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000
FXUS65 KREV 222048
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
148 PM PDT Fri Mar 22 2024

.SYNOPSIS...

Gusty winds and periods of valley rain and mountain snow are expected
over the weekend. Prepare for travel impacts through the Sierra this
weekend. Below average temperatures and unsettled weather will
persist through next week.

&&

.DISCUSSION...

A compact upper cyclone and attendant troughing continues to slowly
approach the West Coast per latest moisture-channel imagery. As a
result, synoptic ascent and mid-level height falls are overspreading
portions of northern California and the Pacific Northwest states.
The overlap of strong ascent with a rich moisture axis has fostered
a band of light to moderate precipitation draped from SW Oregon into
far NW California. The downstream evolution of this band is the key
feature to keep an eye on as it will provide much of the Sierra
snowfall this evening and overnight (more on this later).

Prior to the arrival of rain and snow, winds will increase across
all elevations in response to strengthening 700 mb flow and better
boundary-layer mixing in the afternoon. Ridgetop winds will increase
to 70-90 mph by sunset today while gusts across lower valleys
reach 30-40 mph during much of the afternoon. Sierra crest winds
will remain elevated overnight, but valley winds will diminish in
the evening as the boundary-layer decouples. Additional gusty
winds are expected on Saturday. Plan on some backcountry recreation
impacts, choppy waters on area lakes, and bumpy flights!

The arrival of the rain and Sierra snow will first begin across NE
California south towards the Tahoe Basin between 6-8 PM PDT
according to latest CAM guidance. Showers then move into the Sierra
south of US-50 after 9 PM PDT. Timeframe for peak snowfall rates
(2"/hr) will favor the 10 PM - 2 AM PDT period for the Sierra crest
around/north of the Tahoe Basin and 12 AM - 4 AM PDT for the high
Sierra in Alpine and Mono County. Spillover rain into western Nevada
will initially struggle until the arrival of the cold front late in
the evening. Snow levels will hover near 7000 feet much of the day
before falling to near 5500-6500 feet in concert with heaviest
precipitation rates. Thus, adjacent foothills/Virginia City may see
light snowfall while lower valleys see rain or perhaps as rain/snow
mix Saturday morning. Rain and snow will decrease in coverage and
intensity, while becoming more showery in nature, in the wake of the
cold front passage early Saturday.

The aforementioned trough will phase with the southern jet stream
branch on Saturday, keeping the core of the upper cyclone near the
Oregon coastline. A slow southeast migration of a pocket of cold air
aloft towards the region, which combined with surface heating within
a diffluent flow regime, will yield an increase in shower activity
late Saturday morning into the afternoon. The upper cyclone will
dislodge and become an open-wave feature as it digs south across the
region, providing one final burst of rain and snow to the Sierra and
western Nevada late Saturday into Sunday. A final potential impact
will be a slight chance (10-15%) of thunderstorms/pellet showers
this evening and Saturday afternoon with best chances confined to
the Sierra.

Total snowfall through Sunday along the Sierra crest will vary from
8-14" with a 10-20% chance of receiving 18+". Lower elevation Sierra
communities such as Truckee, South Lake Tahoe, and Mammoth Lakes
will see 2-6" of snowfall with a 20-40% chance of 8+" for the
western Tahoe Basin and areas west of US-395 in Mono County. Light
snowfall up to an inch will be possible (10-30%) near 5500 feet
(i.e. Virginia City). While a few snowflakes may reach valley
floors, accumulation is not expected. Total rainfall across
western Nevada will amount to a few hundredths to a couple tenths.

The synoptic pattern remains active into next week with chances (20-
40%) of light showers on Monday. Our next notable storm appears set
to arrive on Wednesday, bringing another dose of valley rain and
mountain snow showers, gusty winds, and cooler temperatures.

-Salas

&&

.AVIATION...

* A winter storm will affect northeast California, the Sierra, and
  western Nevada this afternoon through Sunday, with the bulk of
  impacts mainly through Saturday morning.

* Winds: A 700 mb jet streak entered the region earlier this
  morning. FL100 winds will continue to increase through the
  afternoon into Saturday morning, peaking around 50 kts. Low-
  level wind shear will occur at all terminals this afternoon
  through Saturday morning. Turbulence is possible above and east
  of the Sierra, too. Surface winds will be from the southwest,
  with gusts of 25-35 kts for all regional terminals.

* Precipitation/CIGs/VIS: The first wave of precipitation moves into
  the Sierra and northeast California after 00Z Saturday. Much of
  the precipitation will begin as -RASN at KTRK (0300-0600Z
  Saturday), KTVL (0200-0600Z Saturday), and KMMH (0600-0900Z
  Saturday), before changing over to snow. Peak snowfall rates of 1-
  2" per hour are expected between 0600Z-1200Z Saturday at
  KTRK/KTVL, leading to IFR/LIFR conditions. KMMH will see snow
  showers between 0600-1500Z Saturday with periods of MVFR/IFR
  conditions possible. Spillover into western Nevada will occur from
  0400-1200Z Saturday, falling mainly as rain, but a few flakes
  could fly, too. MVFR with some intermixed IFR conditions can be
  expected at western Nevada terminals during the aforementioned
  time period. On and off showers will continue into the evening
  Saturday in the Sierra, before another wave of light to moderate
  snow moves over KTRK/KTVL 1100-2100Z Sunday.

-Johnston

&&

.AVALANCHE...

NOTE: The forecast remains on track with no major changes...

For the storm this evening through Saturday AM...

* Liquid totals (SWE): Generally from 0.9-1.4" for the Sierra crest
  west of Tahoe southward to Alpine County, and 0.6-1.1" for Mono
  County.

* Peak Snowfall Rates: Up to 2"/hour for a 3-6 hour period within
  the 10 PM tonight - 4 AM Sat time frame.

* Snow-Liquid Ratios: Starting wetter at 8-10:1, then trending
  somewhat drier at 10-13:1 toward end of event.

* Peak Ridge Level Wind Gusts: 80-90 mph.

-MJD/Salas

&&

.REV Watches/Warnings/Advisories...
NV...Winter Weather Advisory until 11 AM PDT Saturday NVZ002.

     Lake Wind Advisory until 11 PM PDT this evening NVZ004.

CA...Winter Weather Advisory until 11 AM PDT Saturday CAZ071-072.

     Winter Weather Advisory from 5 PM this afternoon to 11 AM PDT
     Saturday CAZ073.

&&

$$


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