625 
FXUS65 KREV 061057
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
257 AM PST Mon Dec 6 2021

.SYNOPSIS...

A fast moving weather system will bring light rain and high
elevation snow later today through tonight. A more potent storm 
will bring an increased chance for snow Wednesday night into 
Thursday, possibly down to lower elevations, with sharply colder 
conditions continuing into next weekend. Next week could be quite  
active with potentially significant winter weather conditions.

&&

.SHORT TERM...through Wednesday...

We can say with certainty that the upcoming week won't be a repeat
of last week's stagnant inversion conditions--now is the time to 
get back into a winter mindset. The persistent high pressure 
ridge has been shoved aside and the first (and weakest) of several
weather systems will make rapid advance into the eastern
Sierra/western NV later today through tonight. Highlights and 
changes are noted here:

* First Precip This Afternoon-Evening: Confidence is higher for a
  swath of light precip (up to 0.10") reaching the Tahoe area and
  possibly far western NV by late afternoon, spreading across
  parts of west central NV this evening. Some of the higher 
  resolution scenarios trended farther north, and we can't rule 
  out a touch of measurable rainfall as far north as Portola-Reno-
  Fallon around the PM commute. 

* More Precip Later Tonight: A second swath of rain and higher
  elevation snow is most likely from US-50 southward. Liquid
  amounts appear to range from 0.05"-0.15", with a few sites
  mainly near the Sierra possibly receiving around 0.25". The
  northern edge of this precip band is again in question, with a
  few scenarios again showing rain reaching into the Portola-
  Reno-Fallon vicinity but most keeping it farther south. 
 
* Snow Levels on the Higher Side: Overall snow levels this
  afternoon look to start out near or above 8000 feet (although
  wet bulb effects may allow for a brief rain-snow mix down to
  near 7000 feet at onset). The snow levels will ease downward
  overnight but largely remain above Lake Tahoe level, with only
  about 20-25% probability of a light dusting at the KTVL/KTRK
  elevations. 
  
* Sierra Snowfall Tonight: For the Tahoe area above 7000-7500
  feet, we're expecting up to 2". For Alpine-Mono counties, a
  little more snowfall is anticipated, generally in the 1-4" range
  above 7500-8000 feet. Anyone traveling over the Sierra area  
  passes and US-395 through Mono county could see minor snow or 
  slush accumulations overnight into Tuesday morning.

For Tuesday-Wednesday, leftover showers for Mineral-Mono counties
end early Tuesday, then we'll have a break until the next system 
arrives late Wednesday into Thursday. Winds will shift to light 
east Tuesday, then start to increase from the southwest Wednesday 
afternoon. These will be the final two days with relatively mild 
conditions (highs mainly upper 40s-mid 50s) before we shift to a 
notably colder regime for a while. MJD

.LONG TERM...Wednesday Night and Beyond...

From Wednesday night into Thursday, there is increasing potential  
for accumulating snowfall and travel impacts across western Nevada 
and the Sierra. A strong cold front associated with an "inside 
slider" trough is poised to quickly sweep across there region on 
Thursday which will allow for snowfall down to all valley floors.

The timing and strength uncertainty remains high, but this is par 
for the course when it comes to slider systems. Nonetheless, some 
aspects including potential impacts are becoming better focused:

* Timing issues remain, but currently the cold front and main
  snowfall band are targeting the Thursday morning time frame. In
  addition, snow showers look to continue behind the front 
  through the afternoon commute. Thursday night could also support
  the development of lake effect snow bands which could lead to 
  localized heavier accumulations southward of larger area lakes. 

* While sliders aren't typically prolific snow producers (unless
  they stall), they do produce widespread impactful snowfall due
  to lower snow levels allowing for a few inches of snow across
  most elevations. Early probabilities of seeing at least 1" inch
  in lower valleys along US-395/I-580 communities is nearly 70%,
  and about a 40% for 2" which is certainly enough to result in
  travel impacts and slowdowns. Sierra communities have a 40%
  chance for 6". These probabilities do not include any additional
  snow from any potential lake effect snow bands. Timing and
  accumulations will become better refined in the 24-48 hour time
  frame ahead of the event.

* It will be much colder behind the front. Temperatures will
  plummet 15-20 degrees, with Friday and Saturday looking quite
  cold, especially in areas that receive snowfall. High
  temperatures Friday in western NV and Sierra valleys look to be
  in the 30s. Frigid temperatures are possible Friday night into
  Saturday morning, with teens and single digits for western NV 
  valleys, and single digits to sub-zero temperatures in the 
  Sierra. 

Below average temperatures are expected to continue through the 
coming weekend with another storm possible early next week. This 
system looks to develop just offshore of the west coast which may 
allow it to tap into deeper subtropical moisture but may have a 
less favorable southerly trajectory. Nonetheless, this has 
potential to be a wetter storm but is still quite a ways off to 
speculate too much on expected precipitation amounts. Fuentes

&&

.AVIATION...

VFR conditions at all terminals through early afternoon, then 
increasing chances for lower CIGS/VIS with mountain obscurations
at the main Sierra and western NV terminals later this afternoon 
through tonight. Most likely precip type will be -RA, although 
there could be a bit of -SN mixing in at times for the Sierra 
terminals, especially at KMMH.

Wind-wise this afternoon and tonight, surface gusts should remain
generally less than 20 kts; however, gusts could reach 55 kts 
over Sierra ridges which could yield some mountain wave turbulence  
or minor shear effects. 

We'll see a break in the weather for Tuesday-Wednesday, then 
probability is high for more impactful conditions with periods of 
IFR/LIFR and snow accumulations, even down to the lower elevation
terminals, Wednesday night into Thursday. MJD

&&

.REV Watches/Warnings/Advisories...
NV...None.
CA...None.

&&

$$

For more information from the National Weather Service visit...
http://weather.gov/reno