Heavy Snow in Arizona, January 20 to 21, 2017

Area Forecast Discussion
National Weather Service Las Vegas NV
937 AM PST Fri Jan 20 2017

.SYNOPSIS...A potent storm system will impact the region today with
widespread rain...gusty winds...and significant mountain snow.
Locally heavy rain may cause flooding concerns across parts of
Northwest Arizona and the Colorado River Valley. Drier conditions
are expected Saturday before another powerful pacific system brings
more rain and mountain snow to the region Sunday into Monday. Dry
and cool conditions last Tuesday through the end of next week.
&&

.UPDATE...Spotter reports/Webcams verify snow falling as far
south as Independence in the Owens Valley. Tricky forecast as I
expect warmer air to invade the Owens Valley later today with snow
levels rising. However, if warm air does not arrive it could snow
much of the day...then taper off this evening.

New Products: Decided to issue a Winter Weather Advisory for the
Owens Valley due to concerns along Highway 395. In addition, issued
a Winter Weather Advisory for the mountains of Death Valley N.P and
elevations above 5000 feet in Esmeralda and Central Nye Counties.

HRRR and operational models showing heaviest band of precipitation
along with the possibility of thunderstorms moving through the
following area:

San Bernardino County, Southern Nye County/Clark County between 1
pm and 5 pm PST.
Colorado River Valley and Northeast Clark County between 3 and 7 pm
PST.
Mohave County between 4 and Midnight MST.
&&

.SHORT TERM...Today through Saturday.

Busy morning preparing for two additional storms headed for the
region through Monday. Main changes this morning:

* Added a Flood Watch for Mohave County, northeast Clark County,
  and the Colorado River Valley this afternoon through tonight due
  to the potential significant rainfall. Those areas received
  0.25-0.75 inches of rain last evening so soils are already
  saturated and additional rainfall is likely to lead to flooding
  issues.

* Added Wind Advisories for San Bernardino, Mohave, and
  southern/eastern Clark Counties for mid-day today into Saturday.
  Expect gusts of 35-45 MPH at times. This includes strong winds and
  possible significant wave activity on Lake Mead and Lake Mohave.

* Expanded the timing and area of Winter Storm Warnings and Winter
  Weather Advisories to include the Sunday-Monday storm system. At
  this time, it appears that this third system may produce to most
  significant snow totals of this series.

Outside of the above, there was just some fine-tuning of the
forecast through the short term period. A California-sized band of
precipitation is moving across the west coast at this time, with
precipitation already impacting the southern Sierra. Expect this
band to move across the region today and tonight bringing widespread
rain and mountain snow. Precipitation will taper off from west to
east tonight through Sunday. As mentioned above, this system will
also be accompanied by gusty winds in many areas along with a chance
of embedded thunderstorms (storms are currently noted on radar over
the Bay Area).

.LONG TERM...Saturday night through Thursday.

Still expecting one final storm system to move through on Sunday
into Monday, which may end up being the strongest and wettest of the
series.  Precipitation is expected to begin overspreading the region
from west to east by early Sunday morning and become heavier and
steadier through the day. Snow levels initially between 4500-5000
feet will gradually rise Sunday evening before crashing back down to
4000-4500 feet Monday morning.  With the deep moisture tap and
impressive vapor transport mentioned in the previous
discussion...there may be localized flooding issues along with
flowing washes and standing water in areas susceptible to these
issues. Rainfall totals in the deserts will average between a half
an inch and 1 inch, with locally higher amounts of 1-2 inches in
some locations.

In the higher elevations above the snow level, significant snow is
expected with snow accumulations of 1-2 feet a good bet Sunday into
Monday morning above 7,000 feet.  Strong winds may impact exposed
areas and ridgelines which will create localized blizzard conditions
as well with low visibility with blowing and drifting snow. This new
snowfall will be on top of the previous two storms which will have
already deposited a deep fresh snow pack. Snow depths in the higher
elevations will be two to four feet or more by early next week
thanks to this storm series.  In areas between 4000 and 6000
feet...a few inches will be possible, especially across northern
Lincoln county where significant totals may be observed as well.
Prepare for the likelihood of winter travel impacts to regional
highways and roadways and plan accordingly. Accumulating snow will
be possible on Interstate 15 near Mountain Pass as well early Monday
morning.

Precipitation will turn more showery Monday and begin to shift east
into Northwest Arizona. Heaviest snowfall in the Mohave county
mountains is likely Monday as colder air filters in, and snowfall
may impact parts of I-40 east of Kingman by late in the day Monday.
Cool and drier conditions will settle in Tuesday through Thursday as
a broad trough sits over the central Rockies. This will keep
temperatures below normal, but generally dry and sunny.  Gusty north
winds are likely to make another visit to the Colorado River valley
Wednesday and Thursday.

&&

.AVIATION...For McCarran...CIGs will be falling through the day with
CIGS at or below 5k expected by 18z if not sooner. Rain expected to
be on the increase, with the heaviest rain expected during the late
afternoon through evening period. CIGs during this time may fall as
low as 2k with widespread mountain obscuration also expected. Gusty
south winds likely through the day. Improving conditions expected
overnight with rain turning more showery and eventually ending by
Saturday morning.

For the rest of southern Nevada...northwest Arizona...and southeast
California...Potent storm system set to impact the region today and
tonight with widespread rain and mountain snow...mountain
obscurations...and low ceilings. Heaviest rain will move from west
to east across the Mojave Desert this afternoon and evening.
Embedded thunderstorms can be expected along with pockets of severe
turbulence. Improving conditions expected late tonight after 6z as
the front pushes east and CIGs and weather improves. Low clouds and
patchy fog will remain possible however across areas mainly north of
I-15.
&&

.SPOTTER INFORMATION STATEMENT...Significant rain and mountain snow
is possible through the weekend. Weather reports of flooding...high
winds...and accumulating snow is requested. Any additional weather
reports related to rainfall...road conditions...or low visibility is
also encouraged.
&&

Update...Pierce

Short Term...Wolcott
Long Term/Aviation....Outler

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LAS VEGAS NV
1044 AM PST FRI JAN 20 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0800 AM     HEAVY SNOW       MT. CHARLESTON          36.26N 115.64W
01/20/2017  M18.0 INCH       CLARK              NV   CO-OP OBSERVER

            MT CHARLESTON COOP MEASURED STORM TOTAL 18
            INCHES WEDNESDAY MORNING TO FRIDAY MORNING.

&&

CFS