Area Forecast Discussion
Issued by NWS Reno, NV

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307
FXUS65 KREV 171223 CCA
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
421 AM PST Tue Jan 17 2017

.SYNOPSIS...

Inversions and poor mixing will continue into this morning. A
thin layer of freezing fog is evident in the 5500-7000 foot range
and may cause slick conditions through late morning. The next
significant weather period is expected to begin late Wednesday.
There is potential for mountain snow and valley rain as another
storm system moves into the region Wednesday night into Thursday.
More storms are possible Friday into the weekend with snow at all
elevations.

&&

.SHORT TERM...

Short range models continue to show a weaker, split-wave,
atmospheric river-type system approaching the Sierra Wednesday
through Thursday. While the intensity of the wave is not as strong
as it was presented 3 days ago or nearly as intense as more recent
precipitation events, there will still be some decent Sierra snow
that will cause travel impacts. As such, Winter Weather Advisories
have been issued from the Oregon border through Mono County.

Today will be the most pleasant day over the next several with
generally benign weather conditions. A thin stratus deck has
reformed in the 5500-7000 ft MSL range along the Sierra Front.
This will cause light ice depositions on surfaces present at these
elevations; roadways could be slick over Mount Rose Highway,
Highway 50 towards Spooner Summit, and around Virginia City. This
stratus layer will rapidly dissipate once winds switch more
southwesterly later this morning.

The next wave will move into the region Wednesday; changes were
mostly minor. Models have sped the wave up by around 6 hrs which
is not uncommon for split-wave systems. QPF trended a little
higher for the Sierra Crest, unchanged across the Tahoe Basin, a
little lower for the Sierra Front, and higher in the Basin and
Range.

Winds begin to increase Wednesday morning especially in the Tahoe
Basin where relatively warmer lake temperatures will aid in
mixing. A Lake Wind Advisory has been issued with gusts generally
to 30 mph around Lake Tahoe in the morning increasing up to 45 mph
in the afternoon. These winds could cause whiteout conditions in the
Sierra. Elsewhere, low level inversions will keep winds decoupled
resulting in turbulence and low level wind shear. By the afternoon,
mixing will increase as the wave moves into the Tahoe Basin. Wind
gusts will increase up to 45 mph with 55 mph gusts possible for more
wind prone areas. Expect travel difficulties along Highway 395
especially for high profile vehicles.

Snow levels and precipitation: Beginning around 7000 feet early
Wednesday morning and rapidly dropping to 5000 feet later
Wednesday evening. QPF totals were not changed too much, but were
lowered along the Sierra Front where shadowing appears to be a
bigger factor. Expect Snow in the Sierra with a rain to rain/snow
transition for the Sierra Front. Fortunately, with shadowing more
prevalent along the Sierra Front, flooding concerns continue to
trend lower. Still, some low-lying areas may see heavy ponding
where drains are clogged with snow.

Accumulations: Expect 3 to 6 inches for Sierra Valleys including
the Tahoe Basin with 6 to 12 inches above 7000 feet. Western
Lassen/Plumas Counties could see 4 to 8 inches west of Highway 395
with up to 4 inches east of Highway 395 through the Surprise
Valley and northern Washoe County. Liquid totals for the Sierra
Front should generally be less than 0.25" with most locations only
picking up about 0.15". The Washoe Valley microclimate could see
more, but still only up to 0.25".

Conditions improve as this initial wave begins to eject Thursday.
Residual snow showers will remain in the Sierra, but there will be
a more definitive break for Western Nevada.

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

Minimal changes made early in the extended forecast as model
simulations are generally in good agreement through about Sunday
afternoon. Early Thursday evening brings a brief break between the
first and second storms...but snow showers will linger in the Sierra
through the night.

The second system remains on track and is forecast to begin
impacting the Sierra and northeast California by early Friday and
continuing through the day. Precipitation should spill into western
Nevada by late morning. Snow levels are still forecast to be near
the valley floors through the bulk of this event. There could be
some areas below 4500 feet that see periods of light rain early
Friday before changing over to or mixing with snow.

Another break develops east of the Sierra early Saturday and lasts
into early Sunday. In these break periods winds could gust a little
stronger...reaching as high as 35-40 mph in some valley locations
east of the Sierra Saturday night or early Sunday morning. Snow may
never fully end in the Sierra and western portions of Lassen and
Plumas counties...but will taper late Saturday.

The third in this series of systems starts moving into northeast
California and the Sierra by early Sunday then spreads east into
western Nevada during the day Sunday. This looks like the more
dynamic and wetter system of the two in the extended period. QPF and
pops were increased for the Sunday time period to account for this
more dynamic nature. The heaviest precipitation looks to be between
12z Sunday and 00z Monday in the current simulations. But there are
some inconsistencies in the models beyond Sunday. The GFS is much
quicker to drive this system east Sunday night into Monday while the
ECMWF holds it in place through Monday. The GEFS ensembles are
tending to favor a slower solution so we will leave the Monday
forecast basically unchanged with a mention of precipitation through
the day. 20

&&

.AVIATION...

Low clouds have moved back into much of western Nevada and the lower
valleys of eastern California this morning on light easterly flow.
Freezing fog is present in some higher valleys in the Sierra as
well. We should see MVFR to IFR conditions across a wide area south
of line from roughly Susanville to Lovelock down to just north of
Hawthorne and Bridgeport...mainly below 6000 feet. Elsewhere skies
are mainly clear.

This will change through the day as a system begins to approach from
the west with increasing high clouds. Low level winds will begin to
shift to a more southerly direction by this evening. That should
help to dissipate the low level clouds. Winds aloft begin to
increase overnight and this will result in low level wind shear for
most terminals by early Wednesday morning.

Precipitation moves into the Sierra and northeast California early
Wednesday. Gusty surface winds are likely east of the Sierra by
Wednesday afternoon...but the precipitation will hold off there
until late Wednesday night. MVFR/IFR conditions are likely in the
Sierra and northeast California by 00z Thursday and MVFR conditions
are possible east of the Sierra by 09z Thursday. 20

&&


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

     Lake Wind Advisory from 10 AM to 4 PM PST Wednesday for Lake
     Tahoe in NVZ002.

     Winter Weather Advisory from 4 PM Wednesday to 4 AM PST Thursday
     NVZ002.

CA...Winter Weather Advisory from 10 AM Wednesday to 4 AM PST
     Thursday CAZ070-071.

     Winter Weather Advisory from 7 PM Wednesday to 7 AM PST Thursday
     above 6000 feet in CAZ073.

     Lake Wind Advisory from 10 AM to 4 PM PST Wednesday for Lake
     Tahoe in CAZ072.

     Winter Weather Advisory from 4 PM Wednesday to 4 AM PST Thursday
     CAZ072.

&&

$$

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



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