Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 131035

Area Forecast Discussion
National Weather Service Reno NV
335 AM PDT Tue Mar 13 2018


A series of winter storms will produce unsettled conditions through
the upcoming week. The first storm will bring gusty winds, rain
and snow this afternoon into Wednesday. A colder storm is
becoming more likely from Thursday into Saturday, producing
additional periods of heavy snow in the Sierra with some snow
accumulation also possible for lower elevations.



Bottom line up front...Significant weather will hamper area travel
from today into the weekend, especially in and around the Sierra.
A strong storm is moving into the region today and will impact
the region through the remainder of the week into the weekend.

Changes primarily concerned increasing precipitation chances
east of the Sierra while raising precipitation totals. The largest
increases in precipitation where more directed into the Basin and
Range where instability is projected to rapidly increase this
afternoon resulting in swaths of moderate showers embedded in
areas of light rain.

Snow levels...starting rather high due to strong southerly flow
ahead of the initial cold front. Cold air aloft moves in this
afternoon resulting in snow levels falling to Sierra Valley
surfaces by early evening. Snow levels continue to fall overnight
tonight towards western Nevada valley floors by mid-morning. The
cold-core of the low settles over the Sierra and western Nevada by

Precipitation...After rain for much of the morning, snow begins
to accumulate in the higher terrain late this morning and down to
pass levels by early afternoon. Accumulations for Lake Tahoe level
will hold off largely until the late afternoon and may initially
be slow to accumulate due to preceding rain. The heaviest period
of accumulation will begin this evening into the overnight hours
resulting in slick conditions, low visibility, and general
difficult travel conditions in and around the Sierra. Totals were
increased around Lake Tahoe with 4 to 8 inches now being projected
through Wednesday afternoon. Heaviest accumulations remain west
of Highway 89, around 1 foot, and above 7000ft to the Sierra
crest, up to 2 feet.

Snow accumulations for western Nevada should hold off until
Wednesday morning and may impact the morning commute; this is
especially true for areas above 5000 feet along the Sierra Front
and around Virginia City. Up to couple inches are most likely
above 5000 feet, but up to 4 inches is possible. Preceding
rainfall will likely limit accumulations along valley floors, but
some slush and slick conditions cannot be ruled out. The best
advice is to expect slick roadways and plan for additional time to

Snow will continue to accumulate in the Sierra and portions of
western Nevada Wednesday night into Thursday, but rates will
taper down significantly.

Winds...A Wind Advisory has been issued for northern Washoe County
and for the Surprise Valley today. Southerly flow is likely to
channel through valleys with gusts up to 55 mph.

Thunderstorms...Instability rapidly increases this afternoon as
the cold-core approaches. Lapse rates steepen and will drive the
potential for isolated convection north of Interstate 80. Another
round of convection is possible Wednesday afternoon as the cold-
core settles over the Sierra and western Nevada. Again, "best"
instability will remain north of Interstate 80.

.LONG TERM...Thursday through Monday...

Confidence in a significant storm system continues to climb for the
Thursday night through Friday night time frame. Operational models
are in good agreement and have shifted to slightly cooler solutions.
This makes snow levels lower and creates a better chance for
accumulating snow in the valleys as well as the higher elevations.

We refined the POPs and QPF a bit for the Thursday through early
Saturday time frame. The latest model solutions support less of a
chance for significant snowfall in the mountains through most of the
day Thursday...but better chances Thursday night into late Friday
night. This includes better spill over potential into western Nevada
for late Thursday night as instability associated with the upper low
increases. This instability is evident in northeast California
earlier Thursday so slight of thunder was added there and far
northern Nevada.

The best time period for precipitation in the mountains extends from
Thursday evening into early Saturday morning while the primary time
for spill over precipitation into areas east of the Sierra looks to
be from about 3 am to around 11 am Friday. This also coincides with
snow levels at the valley floors...increasing chances for snow
accumulation. One note of caution: in mid-March we start to see some
difficulty receiving accumulating snow during the afternoon in areas
generally below 5000 feet due to warming. This will reduce the
overall amount of snow accumulation in the valleys.

The amount of snow currently forecast for eastern California and far
western Nevada...along with the increasing confidence in its
occurrence...has prompted us to issue a watch for most of northeast
California and the Sierra...and the far western part of Nevada...
from Thursday evening through Saturday morning. Any upgrades or
changes to this watch will be handled by subsequent shifts and total
accumulations will be further refined as we get closer to this event.

Models are in better agreement for Saturday as well. The low opens
to a trough and showers linger through the day. There could be
accumulations in the Sierra...but little additional accumulations in
the valleys.

Sunday looks drier...but we should still see lingering showers.
Monday is starting to look like a mainly dry day as a short wave
ridge tries to develop over the region.

Beyond the forecast period there are hints at a return to an active
pattern...but the operational models show little agreement in the
evolution of this pattern.



Precipitation is moving into the Sierra this morning primarily as
rain. Expect snow levels to fall below Sierra terminal elevations
after 20Z with heavy snow accumulations expected in and around
the Tahoe Basin. It will take longer for snow levels to fall for
western Nevada terminals...more toward Wednesday morning.
Accumulations for western Nevada are expected to be light, if any,
through Wednesday afternoon due to warm ground surfaces and
preceding rainfall.

Winds will increase today with area gusts from 30 to 40 kts.
Anticipate LLWS for area terminals today. KRNO tends to have
higher incidence of LLWS with southerly flow, and aircraft should
expect a turbulent approach or departure. Speed shear will be the
issue early this morning as winds increase aloft prior to valley
mixing. Then...gust spread will be more problematic due to
channeling effects from terrain south of the KRNO terminal.
Elsewhere, crosswinds will be more of a concern for KMMH with
stronger turbulence for Sierra terminals.

A few isolated thunderstorms will be possible today and Wednesday
mainly north of Interstate 80; primarily a concern for northerly
approaches to RNO and easterly flight paths to Elko or Salt Lake

Significant weather is expected to continue through the rest of
the week into the weekend. Heavy snow accumulations will be
possible for Sierra terminals with lighter accumulations for the
Sierra Front. Winds will also be problematic as several waves of
activity are expected. Boyd


.REV Watches/Warnings/Advisories...
NV...Winter Storm Watch from Thursday afternoon through late Friday
     night NVZ002-003.

     Wind Advisory from 10 AM this morning to 7 PM PDT this evening

     Winter Storm Warning from 1 PM this afternoon to 11 AM PDT
     Wednesday NVZ002.

     Lake Wind Advisory from noon today to 7 PM PDT this evening for
     Pyramid Lake in NVZ004.

CA...Winter Weather Advisory from 1 PM this afternoon to 11 AM PDT
     Wednesday CAZ071.

     Winter Storm Watch from Thursday afternoon through late Friday
     night CAZ071>073.

     Wind Advisory from 10 AM this morning to 7 PM PDT this evening

     Winter Weather Advisory from 1 PM this afternoon to 11 AM PDT
     Wednesday CAZ073.

     Winter Storm Warning from 1 PM this afternoon to 11 AM PDT
     Wednesday CAZ072.



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