Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 132339 AAA

Area Forecast Discussion
National Weather Service Reno NV
300 PM PST Mon Nov 13 2017


Gusty winds will impact most of the region through tonight. Rain
and high elevation snow will spread into northeast California and
the northern Sierra tonight with difficult travel conditions over
the Sierra Passes. A stronger storm is expected to impact the
region Wednesday into Thursday with heavy rain and heavy mountain
snow, as well as strong winds.



Shortwave passage across northern CA will keep breezy conditions
going through this evening, with stronger gusts most likely across
northeast CA and northwest NV. A narrow band of moisture and
forcing targeted toward the northern Sierra will also accompany
this shortwave passage, leading to a period of rain and high
elevation snow tonight mainly for the Tahoe region. The latest
guidance is projecting QPF up to 0.75 inch near the Sierra crest,
then dropping off to around 0.25 inch around KTRK/KTVL and lesser
amounts for the eastern Tahoe shores. Snow accumulations of 3-8
inches are likely above 7500-8000 feet near the crest. For the
main Sierra passes (Carson, Echo, Donner, Mt. Rose) snow
accumulations should be lighter (up to 3 inches), but even these
small amounts could create slick/slushy travel conditions late
tonight into early Tuesday. For Mono County, precip amounts will
be more limited as the best forcing and moisture stays too far

For western NV tonight, air mass does not become unstable enough and
moisture remains relatively shallow, resulting in strong shadowing
and very little precip reaching the Reno-Carson-Minden-Virginia City

For Tuesday, leftover showers near the Sierra will taper down
quickly as the shortwave departs to the northern Rockies. Winds will
also decrease in lower elevations, while at ridge level there will
not be much of a break in wind speeds, as high elevation winds
increase Tuesday night ahead of the next storm system. MJD

WEDNESDAY AND THURSDAY...A weak/moderate AR (Atmospheric River)
storm is expected to push into the region, bringing heavy rainfall
and heavy high elevation snow. Strong winds are also expected
across the region bringing travel impacts on Wednesday for high
profile vehicles, dangerous boating conditions, and aviation
impacts from low-level wind shear and turbulence.

Models have continued to trend wetter, with integrated vapor
transport now showing inland IVT to 500 kg/(ms). This will be the
most significant storm of the fall season so far, as the tropical
moisture tap will originate from an unnamed tropical disturbance
in the Eastern Pacific. The duration of the AR will be around 9-12
hours of moderate-heavy precipitation. We`ve continued to raise
QPF (and snow amounts), with our latest forecast pushing 2-4" of
precipitation in the Sierra and roughly 0.5-1.5" of rainfall along
the Sierra Front. It does look rather shadowed for western
Nevada, especially early during the event on Wednesday, then the
atmosphere becomes unstable by Wednesday evening, allowing for
more efficient spillover to occur into Western Nevada Wednesday
night. Rivers will nearly double in their current flows Wednesday-
Thursday with this AR storm. No mainstem flooding is expected at
this time. Significant rises on small creeks and streams is expected
at a minimum, but if this becomes wetter than expected, then some
minor flooding could be possible with this storm.

Snow levels still look to be fairly high, around 7000-8000 feet
Wednesday, but then drop quickly Wednesday night/Thursday morning
after the cold frontal passage. Snow levels will drop to below
pass level very early Thursday morning at the tail end of the
event, just as precipitation starts to diminish. Right now the
timing of the lower snow levels should keep the majority of the
impacts for the Sierra passes and limited snowfall for elevations
below 7000 feet. For the High Sierra however, especially above
7500 feet (above 8500 feet in Mono County), there will be
significant snowfall, with many locations seeing over 2 feet of
snow. Timing of the heaviest precipitation looks to be Wednesday
afternoon for the northern Sierra and northeast CA, then Wednesday
evening for the Tahoe Basin and overnight Wednesday night into
Thursday morning for Mono County.

Lastly, a colder secondary wave will move through Thursday night
with snow levels falling down to near valley floors and light
snow accumulations in the foothills above 5000 feet. Hoon


.LONG TERM...Friday through early next week...

The midweek storm is expected to exit western NV by the end of the
week, although some leftover rain and snow showers are possible
Friday morning, with snow levels down near 4500 feet. For the
remainder of Friday into Saturday, a flat ridge will keep dry
conditions with areas of high clouds over the region, with highs a
few degrees below average Friday then trending warmer going into the

Another Pacific storm system is then projected to reach the eastern
Sierra by the Sunday-Monday time frame. This storm currently looks
to be on the warm side with snow levels likely remaining above 8000
feet. The latest guidance is also trending toward a split trough,
but disagrees on whether the split occurs before or after this
trough moves inland. The offshore splitting scenario would keep most
precip limited to the Sierra, while the inland scenario would
potentially bring a short period of rain to lower elevations of
western NV. The longwave pattern downstream seems to be favoring the
ridge prevailing between the Rockies and the central US while a cold
trough digs over the eastern US, which would probably be sufficient
to split the incoming trough before it reaches the Sierra. However,
this is a period of below average forecast confidence due to the
range of possibilities with the track of this trough. At this time,
we will start with better precip chances near the Sierra and
northeast CA, but relatively modest rain chances across western NV
valleys. MJD



Gusty winds (25-35 kt for valleys and 70+ kt for Sierra ridges),
will keep turbulent conditions with mountain waves over the Sierra
and western NV through this evening. Some rotor activity has also
been noted around the lee side terminals (especially KRNO) with wind
direction shifting to south or southeast at times.

Precip tonight will be largely focused over the Tahoe basin, with a
4-6 hour period of steady rain expected at KTVL/KTRK with MVFR
cigs/vis prevailing. There is a low probability (less than 20%
chance) of some snow mixing with the rain at these sites but runways
will remain wet. Lighter precip is possible across northeast CA west
of KSVE and near the Sierra crest in Alpine/Mono counties, with VFR
conditions and very little or no precip expected at the other main
terminals and eastward across west central NV.

After a break Tuesday-Tuesday night other than continued gusty ridge
winds which will likely keep some turbulent conditions near and east
of the Sierra, another storm system begins to affect a larger part
of the region Wednesday through Thursday. This storm will be
stronger with more precipitation, windy conditions, and lowering
snow levels especially by Thursday. MJD


.REV Watches/Warnings/Advisories...
NV...Wind Advisory until 10 PM PST this evening NVZ005.

     Lake Wind Advisory until 10 PM PST this evening for Lake Tahoe
     in NVZ002.

     Winter Storm Watch from Wednesday afternoon through late
     Thursday night NVZ002.

     Lake Wind Advisory until 6 PM PST this evening for Pyramid Lake
     in NVZ004.

CA...Wind Advisory until 10 PM PST this evening CAZ070-071.

     Winter Storm Watch from Wednesday afternoon through late
     Thursday night CAZ071.

     Lake Wind Advisory until 10 PM PST this evening for Lake Tahoe
     in CAZ072.

     Winter Storm Watch from Wednesday afternoon through late
     Thursday night CAZ072.



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