Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 172322

Area Forecast Discussion
National Weather Service Reno NV
322 PM PST Wed Jan 17 2018


A strong winter storm will impact the Sierra and western Nevada
Thursday and Friday. Strong winds will develop Thursday with a
period of heavy snowfall in the mountains late Thursday afternoon
through early Friday morning. There is even potential for snow down
to all valley floors by Friday morning. Periods of blowing snow
along with poor visibility will create hazardous driving conditions,
especially in the Sierra late Thursday through Friday. A weaker
system is expected early next week.



Winter Storm Watches and High Wind Watches have been upgraded to
Warnings for the Sierra and Sierra Front. Additionally, an
Avalanche Watch has been issued for the back-country areas in the
greater Lake Tahoe area. Models remain relatively consistent with
previous runs. There were a couple of minor changes involving
slightly increasing precipitation while increasing snow levels.
However, these changes largely negated one another in terms of
snow accumulation for the Sierra and western Nevada.

Main concerns continue to be:

* Strong gusty winds for Thursday. Forecaster confidence continues
  to be high since high wind signatures remain in place. Winds
  will gust around 60 mph for many locations along the Sierra
  Front. Wind prone locations may gust above 75 mph. Gusts around
  45 mph will be possible for some Sierra locations as well, but
  will be ahead of the main precipitation period. Once
  precipitation starts in the Sierra, winds will begin to decrease
  for the higher elevations. Travel will be difficult with these

* Heavy mountain snow with potential for white-out conditions. No
  large shifts were made to the forecast. Periods of heavy snow
  are still expected Thursday evening and overnight into Friday
  morning. Coupled with winds, expect periods of white-out
  conditions. Travel in the Sierra should be avoided Thursday
  night if possible.

* Western Nevada snow. Low confidence, but potential for high
  impact. Current estimates for snow accumulation around the Reno
  and Carson metros are still less than 1 inch. However, this is
  forecast to fall during the morning commute for Friday morning.
  Past experience suggests that travel delays are possible on area
  roadways, especially with lower amounts expected. Plan for extra
  time for your morning commute.

Further details below:

Models are coming in a little warmer and slower with the initial
wave of moisture. Snow levels were marginally increased by a
couple hundred feet or so to account for these changes.
Additionally, QPF was increased along the crest while lowered in
the Basin and Range; the Sierra Front was not changed by much. In
terms of overall change, these nudges accounted for only a half-
inch decrease in snow accumulations in the Sierra.

QPF and snowfall for western Nevada continues to be elusive. The
current forecast has less than 1 inch of snow based on around a
tenth of an inch in QPF mainly falling along the cold front. One
issue with this forecast is that it is possible that we get closer
to 0.2 inches along the front depending on how vigorous the
frontogenesis is; models handle this type of spill over fairly
poorly. Consequently, there is about a 40% chance in a little more
snow along the front. Still, these totals are fairly small, but
will likely be impactful due to the timing around the Friday
morning commute. Stay tuned on this one.

As for winds, model downslope signatures remain present, but
there has been a slight decrease in 700mb wind speeds in the GFS.
NAM remains robust with 700mb speeds, therefore, will remain
consistent with previous message. Wind speeds remain 55-65 mph at
the 700mb level with ample implications that downsloping will
occur. Bottom line: strong gusty winds will occur along the
Sierra ahead of precipitation and the Sierra Front ahead of the
cold front. Winds will also be gusty for southern Lyon, around
Pyramid Lake, and around Gerlach including the Black Rock Desert.
While the watch was cancelled for southern Lyon County, continue
to expect gusty winds for the Smith and Mason Valleys around 45
mph. Blowing dust will likely occur in the Basin and Range as well
with these winds. Boyd

.LONG TERM...Sunday through Wednesday...

The next low pressure system moves into the Pacific Northwest and
into Northern CA/NV on Sunday. The overall trend for this system has
been weaker as the moisture field has been splitting with a bulk of
the moisture staying northward. Moisture does make it through into
the Sierra and western Nevada but the expected amounts have
decreased. Nonetheless, still can see a few inches of snowfall
across the Sierra mainly through Monday morning. Anyone with travel
plans Sunday night into Monday morning should be prepared for winter
driving conditions in the Sierra. A slick commute is also still
possible for western Nevada valleys from a mix of rain and snow.

Another low pressure storm system looks to pass through the Sierra
and western Nevada midweek, but still a little early to discuss
details. Overall, it looks to a progressive system which provides
precipitation across the area through Thursday afternoon. Global
models still vary widely on the expected moisture content on this
system, but for now continue to monitor the forecast if you have
outdoor or travel plans during the middle of next week. Fuentes



A Winter Storm will impact the Sierra and western Nevada terminals
on Thursday. Impacts include: strong and gusty winds, turbulence and
wind shear, accumulating snowfall for Sierra terminals.

*WIND: Winds increase first across the Sierra ridgetops this evening
with areas of moderate turbulence developing. Wind gusts will
strengthen to near 100 kts with moderate to severe mountain wave
turbulence expected through the Sierra by Thursday morning.

Terminals should begin to see strong winds develop after 18-20z with
gusts at area terminals reaching 35-50 kts. Low-level wind shear,
moderate to severe mountain wave turbulence and rotors downwind of
the Sierra are possible. Winds will begin to decrease behind the
cold frontal passage sometime Thursday evening after 06z.

*RAIN & SNOW:  Snow begins at KTRK and KTVL after 00z Thursday
afternoon (06z KMMH) with periods of moderate to heavy snow possible
in the 03-15z window (09-18Z KMMH). Gusty winds and high
ratio(dry/light)snowfall may produce periods of zero visibility
(white out conditions) in blowing snow. Accumulations of 4-6 inches
are possible for KTRK/TVL, 2-4 inches at KMMH through Friday

KRNO and KCXP will see light rainfall by Thursday evening with a
change over to snow expected behind the front around 10-12z. A light
snowfall accumulation of 0.5-1.0" is possible Friday morning. Fuentes


.REV Watches/Warnings/Advisories...
NV...Lake Wind Advisory from 10 PM this evening to 4 PM PST
     Thursday for Lake Tahoe in NVZ002.

     Winter Storm Warning from 4 PM Thursday to 4 PM PST Friday

     High Wind Warning from 10 AM to 10 PM PST Thursday NVZ003.

     Lake Wind Advisory from 4 AM to 7 PM PST Thursday for Pyramid
     Lake in NVZ004.

CA...Winter Weather Advisory from noon Thursday to 10 AM PST Friday

     High Wind Warning from 4 PM Thursday to 4 AM PST Friday CAZ073.

 Lake Wind Advisory from 10 PM this evening to 4 PM PST Thursday
 for Lake Tahoe in CAZ072.

     Winter Storm Warning from 4 PM Thursday to 4 PM PST Friday



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