627
FXUS65 KREV 121123
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
323 AM PST Wed Feb 12 2025

.SYNOPSIS...

* A significant winter storm will bring periods of heavy Sierra
  snow, rain and light snow to valleys, and gusty winds tonight
  through Friday.

* There is the potential for greater snowfall on Sierra Front valley
  floors Thursday with higher snow impacts.

* Drier conditions return on Saturday with a weak storm possible
  Sunday into early next week.

&&

.DISCUSSION...

Who needs coffee to wake up in the AM when you`re met with
temperatures in the teens and single digits as you head out the
door? That`ll be the case once again this morning as cold weather
continues to be the main headline much of today before the arrival
of potent winter storm tonight (more details below). It`ll be
particularly cold near the Oregon border where temperatures struggle
to exceed the 20s. Elsewhere, expect daytime highs in the 30s and
40s.

Our much anticipated winter storm arrives tonight, yielding periods
of heavy Sierra snow, a blend of rain and snow for valleys, and
gusty winds through Friday. Snow showers begin to increase in
coverage and intensity across the Sierra after 7 PM PST with peak
snowfall rates of 2-3"/hr still favoring the mid-morning to early
afternoon hours ahead of an advancing cold front. Snow levels may
lift enough to allow periods of rain at lake level and below 7000`
in Mono County Thursday morning, but will switch back to snow in the
afternoon when the cold front passes. Latest CAMs advertise a very
brief lull in shower activity in the afternoon as we transition into
the colder side of the storm, but rain and snow quickly become
reinvigorated by the mid-afternoon/early evening as the pocket of
coldest air aloft approaches. A few flashes of lightning will also
be possible on Thursday with best chances (10-15%) in the afternoon
and evening. Snow showers linger through much Friday before tapering
off into Saturday morning. The AM forecast suite is still holding
steady on multiple feet of total snowfall along the Sierra crest,
around a foot of snow for Tahoe Basin communities (e.g., Truckee,
South Lake Tahoe) with up to 2 feet along western Tahoe shores, and
6-12" for foothill areas and Virgina City by Saturday morning.

The fly in the ointment continues to be the prospect of a snow event
for Sierra Front cities (e.g., Reno, Sparks, Carson City, Minden) as
there is still uncertainty in snow levels and spillover efficiency.
There`s high confidence that when showers begin late tonight, it
will be in the form of snow given our antecedent cold airmass. We`ll
likely see at least a couple hours of light snow early Thursday
morning, in which a quick dusting to an inch will be possible on
valley floors. Thereafter, "boom/bust" potential increases from mid-
morning onward as a couple scenarios with two very different
outcomes are plausible. The first is the "boom" scenario in which a
residual, sub/near-freezing layer allows for prolonged period of
steady, wet snow down to valley floors. Should this scenario occur,
snow totals would be much higher than anticipated and snow impacts
would be greater. The "bust" scenario could resemble two options: 1)
Sufficient mixing/warming at the surface to lift snow levels just
above valley floors and switch snow to rain and/or 2) a more
effective shadowing effect through Thursday AM that would limit
spillover into western Nevada and augment wind impacts. Either of
the two would limit snowfall and preclude greater snow impacts.

As of now, latest hi-res guidance is siding with the "bust" scenario
with light snowfall Thursday AM becoming rain by Thursday afternoon,
thus we`ll hold off on upgrading to a Winter Storm Warning for now.
However, this may change very quickly as we get updated model
guidance so make sure you keep up with the latest forecast and plan
accordingly! The storm will wind down late Friday into Saturday with
perhaps a few lingering snow showers. We`ll be mostly dry for
Saturday into early Sunday before a weak storm increases chances for
showers into early next week.

-Salas

&&

.AVIATION...

Widespread VFR conditions and light breezes will persist through
much of the day before the arrival of strong winter storm
deteriorates flight conditions late tonight through Friday.

Periods of moderate to heavy snow will reduce CIGS/VIS to IFR/LIFR
conditions late tonight through Friday with heaviest snow expected
between 12z and 00z. Snow may switch to rain Thursday morning before
changing back to snow Thursday afternoon. There is also the
potential for a very brief lull in the showers Thursday afternoon
(between 21-00z) when CIGS/VIS may improve, but a second wave of
heavier snow quickly follows in the late afternoon. Expect
significant runway accumulation through Friday at Sierra terminals.

For RNO/CXP/MEV, light snow will most likely fall early Thursday AM
and yield MVFR/IFR conditions through mid-morning before snow
switches to rain (think more MVFR and mountain obscuration
concerns). However, there is the potential that it stays snowing
through Thursday, in which a more extensive period of IFR conditions
and several inches of runway snow accumulation would be more likely.

LLWS and mountain wave turbulence is expected after midnight tonight
as FL1000 winds strengthen to 60-80 kts between the 12z-21z
timeframe.

-Salas

&&

.AVALANCHE...

Widespread wind with heavy snow impacts across all avalanche center
terrain expected tonight through Friday evening.

* SWE Totals: Still expecting between 3-5" for all avalanche centers
  in a 48 hour period.

* Snow-Liquid Ratios: Snow liquid ratios across all avalanche
  centers start near 12:1 tonight into Thursday morning. Snow ratios
  then decrease closer to 8-10:1 on Thursday afternoon, then once
  again increase to 12-14:1 by Thursday night into Friday.

* Snow levels: For the Sierra Avalanche Center, snow levels tonight
  into Thursday morning are below 5,000`. Snow levels then increase
  on Thursday afternoon to around 6,000`, then once again fall to
  around 5,000` through Friday. For the Bridgeport and Eastern
  Sierra Avalanche centers, snow levels start below 6,000`, then
  increase to around 6,500-7,000` by Thursday afternoon. Snow levels
  then fall again below 6,000` Thursday night into Friday.

* Snowfall totals: There is a likely 80+% chance for 2-4 feet of
  snowfall across all avalanche centers in a 48 hour period. Peak
  snowfall rates of 1-3"/hr are also likely for the duration of the
  event.

* There is a 10-15% chance of lightning on Thursday, favoring the
  crests for all avalanche centers.

* Ridge top gusts: Strong SW/W gusts of 70-90 mph along exposed
  Sierra ridges through Friday AM, weakening Friday afternoon.

-McKellar/Salas

&&

.REV Watches/Warnings/Advisories...
NV...Cold Weather Advisory until 8 AM PST this morning NVZ005.

     Winter Storm Warning from 10 PM this evening to 10 PM PST Friday
     NVZ002.

     Winter Storm Watch from late tonight through late Thursday night
     NVZ003.

CA...Cold Weather Advisory until 8 AM PST this morning CAZ070.

     Winter Storm Warning from 10 PM this evening to 10 PM PST Friday
     CAZ071>073.

&&

$$