Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 171051
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
251 AM PST Wed Jan 17 2018

.SYNOPSIS...

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.

&&

.SHORT TERM...

Mild weather today with cloudy skies and above average temperatures
ahead of the next storm. No major changes this morning as
simulations remain on track to bring a strong Pacific storm into the
Sierra and western Nevada. Strong winds, heavy mountain snows and
rain accompany the storm`s arrival on Thursday and Friday. This will
be a fairly typical January winter storm (even though we haven`t had
many) and beneficial to boost snowpack for the lower and mid
mountain elevations.

Primary Concerns:

* Strong winds Thursday (high confidence) - Increased risk of
  turbulence and wind shear for aviation. Impacts to transportation
  along wind prone highways, such as Highway 395 and Interstate 580.
  Check road restrictions before you go, as high profile vehicles
  may have to reroute. Today is the time to secure all outdoor items
  and double check fences and gates. Power outages will be possible
  for areas where wind gusts exceed 65 to 70 mph.

* Heavy Mountain Snows (high confidence) - Periods of heavy snow
  along with strong winds will produce poor visibility with
  localized whiteout conditions late Thursday into Friday. Plan on
  commute headaches due to snow and poor visibility for Thursday PM
  and Friday AM commutes.

* Snow for Western NV (low confidence) - Latest simulations show
  rain impacting the Thursday PM commute in western NV with the
  changeover to snow Friday morning before 7AM. Snow amounts are
  still uncertain but generally 1/2"-3" will be possible. Regardless
  of snow or rain amounts, plan on slick roads for both commutes.
  Studies show that more accidents occur with accumulations of 1
  inch or less than the higher snow amounts.

Those are the primary forecasting concerns for now. For more details
on each, keep reading...

Winds pick up early Thursday morning ahead of the cold front as 700
mb flow increases to 50-60 kts. Forecast soundings have been
consistent with showing a persistent stable layer just above the
ridgeline beginning early Thursday morning and persisting until late
Thursday or even early Friday morning. This stable layer will allow
stronger upper level flow of 50-60 kts to be forced down to the
valley floors as widespread wind gusts between 50 to 60 mph. Wind
prone locations can expect wind gusts up to 80 mph at times on
Thursday. This downslope signature has been fairly consistent over
the past few model forecasts so forecaster confidence is high for
high winds to materialize.

Once the strong cold front passes through the region, winds should
begin to dissipate. Model soundings and cross sections show the
atmosphere quickly destabilizing (bye bye stable layer at the
ridgeline) with cold frontal passage which will allow for spillover
to dampen the surface winds gusts along the Sierra front. Winds will
likely persist further south for Alpine and Mono counties as cold
frontal passage will not occur until later in the morning on Friday.

The biggest question will be the potential for snow in the lower
elevations of western Nevada. This will be determined by the
location of the very cold air behind the cold front as well as the
moisture associated with the storm. Simulations for now show the
potential for a quick burst of snow along the cold front between 1AM-
5AM on Friday morning for the Reno urban areas. Thankfully the cold
front will be moving through quickly so snow amounts should remain
on the low end, but it is best to assume the morning commute will be
rather slow. There is always the potential for more convective snow
bands to develop behind the front during the day on Friday, where it
will seem like the snow/low visibility "came out of nowhere". -Edan

.LONG TERM...Saturday through Tuesday...

We will see a short break in the weather Saturday and Saturday
night as weak high pressure builds over the region. By Sunday,
another push of moisture moves into the Pacific Northwest and into
Northern CA/NV. There is a decent plume of moisture out there
over the Pacific, but latest models continue trending further
north with the shortwave passage and main AR landfall. This will
result in northern CA/NV getting less precipitation than models
were suggesting just a couple days ago.

We have backed off a little on QPF/snow amounts for the
Sunday/Monday storm system, but still expect to see several
inches of snow in the Sierra and around Lake Tahoe lake level,
potentially up to a foot along the Sierra Crest from Lake Tahoe
northward to Lassen County. Snow levels could rise up to near
5500 feet by Monday morning with a mix of rain/snow accumulations
in the lower valleys of northeast CA and western NV. Anyone with
travel plans Sunday into Monday morning should be prepared for
winter driving conditions in the Sierra. Monday morning`s commute
could get slick if snow levels remain at valley floors, so we will
need to monitor this latest trend.

Another weak storm system should move into the region late Tuesday
into Wednesday, although this storm is also trending further north
into the Pacific Northwest. -Hoon

&&

.AVIATION...

A ridge of high pressure will build over northeast CA and western
NV, bringing precipitation-free conditions although plenty of mid
to high clouds could persist. Turbulence looks generally low
(near and below ridges) with modest winds over ridges and mainly
light flow near the surface. Patchy fog is expected near KTRK
through 16z this morning.

A strong cold front will move into the region Thursday into
Friday. Thursday`s winds will be quite strong, especially within
about 6 hours of FROPA, with wind gusts at area terminals 35-50
kts, causing low-level wind shear and moderate to severe mountain
wave turbulence over and downwind of the Sierra. This storm will
also bring snow or rain quickly changing to snow to the region
Thursday night into Friday, along with at least periodic MVFR/IFR
CIG/VIS to area terminals. A light accumulation (up to an inch) is
possible for western NV terminals. -Snyder/Hoon

&&

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

     High Wind Watch from Thursday afternoon through late Thursday
     night NVZ001.

     High Wind Watch from Thursday morning through Thursday evening
     NVZ003.

CA...Winter Storm Watch from Thursday afternoon through Friday
     afternoon CAZ071-072.

     High Wind Watch from Thursday afternoon through late Thursday
     night CAZ073.

&&

$$

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



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