Reno Area Technical Forecast Discussion

Technical Forecast Discussion

000
FXUS65 KREV 290951
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
251 AM PDT Fri Mar 29 2024

.SYNOPSIS...

The next storm arrives today into the Sierra, western Nevada and
northeast California bringing waves of valley rain and rain/snow
mix, and mountain snow through the holiday weekend. Mild and
drier conditions along with gusty winds for the Eastern Sierra
return early next week. However, active weather returns with gusty
winds and periods of rain and snow for the second half of the
week.

&&

.DISCUSSION...

Hopefully, you got to enjoy the break we got from the appetizer
storm yesterday as active conditions return today. The main entree
arrives this weekend to the region. Currently, two upper level
lows are circling each other in the Eastern Pacific. One of them
strengthens and absorbs the other low while moving closer towards
the CA coast later today. Bands of rain and snow are expected
with this system starting over the Sierra and NE CA, before
quickly moving into western NV.

Bottom Line up Front: Expect periods of valley rain or rain/snow
mix and mountain snow through Sunday. Winter Weather Warnings for
much of the Sierra and Advisories for Reno-Carson City-Minden to
Mineral Co. and NE CA are in effect through Sunday. Main hazard
is snow with the Sierra crest near the Tahoe Basin having a 30-60%
chance of exceeding 12" through Sunday, Mono Co. 50-80%, and
Lassen/Plumas 10-30%. For Sierra communities from Mono Co. to the
Tahoe Basin and into Lassen Co., the probability of exceeding 12
inches is below 30%. For western NV Highlands and hills the
probability of exceeding 6 inches through Sunday is 20-50%, and up
to 20% for amounts greater than 12 inches. Drier and above
average temperatures, along with gusty winds in the Sierra
ridgetops are expected early next week. Active weather returns for
the second half of the week with gusty winds and periods of rain
and snow.

More details about the forecast are found below:

On Friday, periods of valley rain and mountain snow will prevail
starting late in the morning/early afternoon. Snow levels fluctuate
between 4500 to 5500 ft this morning but will slightly increase
to 5000-6000 ft by the afternoon. So, hills may see some light
snow late in the morning, but then transition to rain in the
afternoon over western NV. The Sierra will pretty much observe
rounds of snow. HREF shows multiple bands of showers passing
through Saturday morning with snowfall rates generally below 1
inch per hour in the Tahoe Basin, and 1-2 inches per hour for the
Sierra crest in Mono Co. There is a low chance for higher snow
fall rates up to 3 inches near the crest by Mono Co., especially
in the far southern areas in the evening and overnight hours.

On Saturday, as the low slowly descends along the CA coast we
will be situated close to the deformation zone, meaning that more
air ascends due to the diffluence aloft. Therefore, expect mostly
snow showers to continue areawide, with rain confined mainly to
valley floors. Snow levels on Saturday morning will be between
4000-5000 feet. Furthermore, the low appears to split again into
two upper lows resulting in a very dynamic and unstable environment.
This will result in more showery and convective cells across the
area compared to the more stratiform bands in the previous day.
Convective cells mean that we could see more bursts of rain and
snow. Latest HRRR and NAM are highlighting western NV as the area
of concern with the Sierra having breaks during the daytime hours.

By Sunday, we will be dealing with the wrap-around moisture of
this system as it slowly tracks east over the Great Basin. Therefore,
precipitation amounts will be mostly light. We need to have at
least one or two model runs of high-res data to see how Sunday
pans out. Overall, this should be the end of the event as upper
level dynamics deteriorate, and we become less unstable for the
development of more rain/snow.

Winds should not be much of a problem through the weekend. Gusty
winds are mainly expected at the Sierra crest through Sunday,
which is typical with any storm system. Breezy conditions appear
to develop in NE CA and far north Washoe Co. near the OR border
on Sunday afternoon, but will not be significantly impactful.

Early next week, we will have a well deserved break as an upper
ridge moves into the western US. Although with the exiting trough
taking a more southeasterly trajectory it will lead to east to
northeast Sierra ridge winds. These winds may bring some impacts
to aviation and backcountry recreation. At least, it doesn`t
appear to be as much of a significant wind event compared to the
last one a few weeks ago. Anyway, drier and warmer conditions are
expected with afternoon temperatures reaching above average values
between Tuesday and Wednesday across the area.

For the second half of the week, models continue to indicate the
return of unsettled weather with a another trough/closed low
descending into the PacNW and the Great Basin. So, we may see more
periods of valley rain and mountain snow. Of greater concern are
the winds associated with this system, as the latest model run
show the possibility of strong winds in the Sierra and western NV
mountain areas (30-60% Sierra crest & 10-50% W NV mountains for
winds above 60 mph).

Crespo

&&

.AVIATION...

PRECIPITATION: Multiple rounds of Sierra snow, and a mix of
rain/snow to valley areas will result in periods of MVFR/IFR
conditions in the Sierra for KTRK-KTVL-KMMH starting around 18-21Z
today that continues through Sunday afternoon before the upper
trough slowly exits east out of the region Monday. There is at
least a 15% chance for LIFR conditions in both VIS/CIG between
06-15Z Saturday for these Sierra terminals. Sierra terminals also
have a 50-60% chance for 6+” of snowfall on runway surfaces. There
is a slight chance for periods of light snow and brief periods of
IFR conditions late Saturday into early Sunday morning for
western NV terminals (KRNO/KCXP/KMEV) as well. Blended forecast
guidance, however, shows less than a 15-20% chance of any
accumulating snow at this time. Otherwise look for periods of
VFR/MVFR conditions in showers for western NV through Sunday.

WINDS: FL100 winds across the Sierra and western Nevada today will
be from the south up to 20kts before shifting more east-southeasterly
on Saturday. Surface winds will generally be from the south-
southeast 10-20kts today for most regional terminals with winds
shifting more westerly through Saturday. -Amanda

&&

.AVALANCHE...

The next storm pushes into the Sierra today and brings multiple
waves of precipitation through Sunday afternoon.

* Liquid totals (SWE): For Mono county above 7000 feet, 0.5" – 2.25"
  from Friday through Sunday afternoon. For the Tahoe Basin along
  the crest 1.5"-2.5", and around 1-1.25" in the Basin.

* Peak Snowfall Rates: For the Tahoe Basin, 1-2" per hour rates
  will be possible Friday afternoon with another round possible
  after 8pm til midnight. For Mono County, the best time frame
  for 1-3" per hour rates in the high Sierra appears to be 8pm
  until 4am on Saturday for now.

* Snow-Liquid Ratios: Drier snow ratios around 10-14:1 for much of
  the storm.

* Peak Ridge Level Wind Gusts: Winds won`t be as strong with this
  storm with peak wind gusts 40 to 50 mph possible along the Eastern
  Sierra crest.

-Amanda/Edan

&&

.REV Watches/Warnings/Advisories...
NV...Winter Weather Advisory from 11 AM Friday to 5 PM PDT Sunday
     Nvz001-003.

 Winter Storm Warning from 11 AM Friday to 5 PM PDT Sunday Nvz001.

CA...Winter Weather Advisory from 11 AM Friday to 5 PM PDT Sunday
     Caz071.

     Winter Storm Warning from 11 AM Friday to 5 PM PDT Sunday
     Caz071-073.

&&

$$

NWS REV Office Area Forecast Discussion