Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 191819

Area Forecast Discussion
National Weather Service Reno NV
1019 AM PST Thu Jan 19 2017

Snow showers continue in the Sierra with the next system arriving
late tonight and continuing into Saturday with the biggest storm
arriving Saturday night into Sunday. Overall, the same ideas
apply, but to simplify messaging and to really convey the
potential impact of this latest series of storms we have made some
changes this morning. Tahoe/Mono upgraded to warnings effective
immediately and continuing through Monday morning as snow showers
will continue to be locally heavy. The Lassen warning will run
12Z Fri through 12Z Mon. Left the advisories for Western NV as is,
but added a Winter Storm Watch for the Sierra Front Sunday and
Sunday night.

The bottom line is this, several feet of snow are likely in the
Eastern Sierra through the weekend with 2 feet or more possible
for the foothills of western NV. With snow removal becoming an
issue, and the heavy snowfall expected, major travel disruptions
are likely. In fact, if you live in the Tahoe Basin, Mono County
or even Virginia City, be prepared to be snow bound for at least a
couple days in the worst case scenario. More details on the storm
this afternoon. Wallmann



Snow showers will diminish this morning with a brief lull in the
weather until the next storm arrives early Friday morning.
Significant winter weather driving slow downs will continue in  the
Sierra with possible slow downs across western Nevada valleys  by
the Friday morning commute. A more potent winter storm is  expected
for Sunday and Monday. Much drier weather is possible by  the middle
of next week.


.PREVIOUS DISCUSSION... /Issued 335 AM PST Thu Jan 19 2017/


The first in a series of winter weather systems continues to push
across the Sierra with a few spillover rain and snow showers making
their way across the Hwy 395 corridor from the North Valleys into
the Carson Valley. Little to no accumulations expected on valley
floors but locations roughly above 5,000` may see a dusting to
upwards of an inch this morning. Chain restrictions remain in place
for much of the Sierra and area roadcams show snow covered roads
through the Tahoe Basin and Mono County. Based on the latest radar
trends and hi-res short term model simulations, will keep the
Winter Weather Advisory running through 10am this morning across
the Tahoe Basin and Mono County.

Snow will thin out and become more light and showery by late morning
and early afternoon. The bottom line is that winter driving
conditions will be nearly continuous in the Sierra into early next
week with lighter periods such as this afternoon and evening,
followed by heavier episodes on Friday and Sunday. Those that
must travel through the Sierra should closely follow the forecast
as travel maybe significantly impacted by early Friday
morning/afternoon with an increasing potential for a strong and
significant winter storm Sunday in the Sierra which may also
result in significant western Nevada snowfall accumulations as
well. For more details on this system is the Long Term forecast
section below.

After our brief lull this afternoon and evening, the next winter
system will begin to impact the Sierra and western Nevada early
Friday morning into Saturday morning. Winter Weather Advisories have
been posted for this next system during this period across the
Sierra and also for western Nevada where spillover and low snow
levels should allow for snow accumulation on valleys floors.

Snow levels early Friday morning look to start generally around
4,000` and raise about near 4,500` during the afternoon Friday which
may mix some rain into the lower valley elevations. Snow totals
from Friday morning through Saturday morning in the Sierra look
to be in the 12-18" above 7,000` (Tahoe & Mono) with closer to
6-12" for lake level. This storm will have a better shot at
producing snow on western Nevada valley floors than our current
system, with valleys having a chance at seeing 1-3" of snow with
foothill areas seeing 2-5". Timing for western Nevada snowfall
looks to be right around the early Friday morning commute so
significant traffic slow downs will be possible, so give yourself
extra time to reach your destination. Fuentes

LONG TERM...Saturday through Wednesday...

Primary changes to the extended forecast this cycle were to increase
pops Sunday and Monday and increase QPF Sunday and Sunday evening.

Model simulations are still on track with a dynamic cold system
pushing into the region late Saturday night and persisting over the
area through early Monday. Ahead of this system some lingering snow
showers will continue in the Sierra through Saturday. Gusty winds
are likely ahead of the system Saturday afternoon and evening for
much of the area with the strongest winds in the Sierra and just
east of the Sierra into the valleys of northeast California and
western Nevada.

The system for Sunday comes with a very strong jet aloft...150+ kt.
Early on this system will tap a fairly deep moisture plume in the
eastern Pacific. The tapping of this moisture plume in the model
simulations has resulted in increased QPF for the past few model
runs. This is true today as well...and we may need to increase the
QPF even more with time. The good news from a flooding perspective
is that snow levels should be low enough with this system that only
the very lowest valley floors in Pershing and Churchill counties see
any rain or rain/snow mix. The moisture push comes in two distinct
segments. The first is during the day Sunday when mainly the Sierra
and northeast California see the brunt of the precipitation. Then
another burst develops Sunday evening associated with a secondary
vorticity lobe and surface cold front. This is likely to put
significant snow accumulation in the western Nevada and northeast
California valleys. It is highly likely that if the models continue
this trend we will see in excess of 6 inches of snow on the valley
floors west of Highway 95 through Monday morning to go along with up
to 3 feet in the higher elevations of the Sierra and near 2 feet
around Lake Tahoe and near Mammoth Lakes. This would require Winter
Storm Warnings. With the current advisories in place for earlier
systems...we will hold off on these to avoid confusion.

Snow showers linger into Monday afternoon and even into early
Tuesday morning. Then a ridge begins to build over the region. With
snow cover for much of the area that will mean valley inversions
with well below temperatures and poor air quality into the middle
part of next week at least. High temperatures were lowered from
Sunday through Tuesday to reflect the presence of snow and the cold
air trapped in the valleys. 20


Snow showers with MVFR/IFR cigs/vsbys will continue in the Sierra
today while areas to the north and east receive a brief break later
this afternoon. Winds should not be overly strong at the surface
today...gusts 25-30 kts...but will remain quite strong over the turbulence is likely.

The next system is slated to move into the area later tonight and
affect a large area Friday into Friday night. Additional snow
accumulations of 6-10 inches are possible at KTRK/KTVL with up to 5
inches at KMMH. KRNO/KCXP could see up to 3 inches by early
Saturday morning. MVFR/IFR conditions develop for much of the area
late tonight with the lowest cigs/vsbys in the Sierra.

Another break occurs east of the Sierra Saturday...but then a
third...much stronger...system drives into northern California and
western Nevada late Saturday night into Sunday. This storm should
spread accumulating snow throughout the entire region with 4-8
inches in the lower valleys before the snow ends late Monday. Gusty
winds could also precede this storm Saturday afternoon and evening
with turbulence aloft and low level wind shear near the terminals. 20


.REV Watches/Warnings/Advisories...
NV...Winter Weather Advisory from 4 AM to 10 PM PST Friday NVZ005.

     Winter Weather Advisory until 10 AM PST Saturday NVZ002.

     Winter Storm Watch from Saturday evening through late Sunday
     night NVZ002.

     Winter Weather Advisory from 4 AM to 10 PM PST Friday NVZ003.

     Winter Storm Watch from Saturday evening through late Sunday
     night NVZ003.

CA...Winter Weather Advisory from 4 AM Friday to 4 AM PST Saturday

     Winter Storm Watch from Saturday evening through late Sunday
     night CAZ071.

     Winter Weather Advisory from 4 AM to 10 PM PST Friday CAZ070.

     Winter Weather Advisory until 10 AM PST Saturday CAZ073.

     Winter Storm Watch from Saturday evening through late Sunday
     night CAZ073.

     Winter Weather Advisory until 10 AM PST Saturday CAZ072.

     Winter Storm Watch from Saturday evening through late Sunday
     night CAZ072.



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