Heavy Snow in Nevada, March 17, 2018

Area Forecast Discussion
National Weather Service Las Vegas NV
928 AM PDT Sat Mar 17 2018

.SYNOPSIS...Upper low moving through the area will bring another
unsettled day with chances of rain and mountain snow across portions
of the southern Great Basin and Mojave Desert. Calmer and drier
conditions are expected Sunday through at least Tuesday as high
pressure builds over the area.
&&

.UPDATE...Upper low initialized near the triple point of OR/CA/NV
this morning. Jet streak along with upper level disturbances will
keep narrow lines of rain/snow showers mainly across Lincoln County
from now through 8 pm this evening. Precipitation looks light with
generally 1-3 inches of snow, locally higher amounts in the Wilson
Creek and White Rock Mountains of northeast Lincoln County. During
the overnight hours focus shift southeast primarily across eastern
Clark and all of Mohave Counties. Potent shortwave pivoting through
base of trough across southern California/Arizona will initiate
several convective lines of rain/snow showers. 12z models hitting
northern Mohave County with slightly higher precipitation amounts
during the overnight hours. Did create some new total snow grids
based on the slightly higher precipitation amounts. It did not make
much change from the previous forecast with generally 1-3 inches
populated areas along Highway 389 in far northern Mohave County.
Some of the higher plateaus/mountains may see 3-6 inches. Due to the
limited impact decided not to issue a Winter Weather Advisory.
Conditions in Mohave County should quickly improve shortly after
daybreak Sunday.
&&

.SHORT TERM...Through Sunday.

Broad upper low moving onshore just north of the CA/OR border will
continue to push inland today and help bring unsettled weather into
Sunday. We will see a couple of vort lobes rotating around the low
affect our area today which will help enhance some of the shower
activity today. Showers should be generally isolated over much of
the area with more scattered showers developing across Lincoln and
northern Mohave Counties. An isolated thunderstorm or two can't be
ruled out over those areas along with some small hail due to the
increased instability as the vort max pushes through this afternoon.
Models are indicating more widespread precipitation developing this
evening over northern Mohave County in an area of upper difluence.
Snow levels are forecast to be around 4500 feet and could possibly
lower to around 4000 feet in heavier precipitation. Places like
Colorado City and Pipe Spring National Monument could see a couple
of inches of snow, but at this time any winter weather advisories
are not expected. Precipitation will gradually shift east overnight
with some residual showers Sunday morning. By Sunday afternoon much
of the area is expected to be dry.

Breezy conditions will remain over the area once again today with
most areas seeing winds 15-25 mph with gusts to around 30 mph. Winds
are not expected to reach advisory levels anywhere today. Northwest
flow will develop over the area Sunday with winds mainly 10-20 mph.

Temperatures are expected to remain about 10 degrees below normal
today and Sunday.

.LONG TERM...Sunday night through next Saturday.

Active weather pattern will continue through the long term, though
details related to precipitation timing remain unclear.  Starting
Sunday night, our region will be in between weather systems with a
shortwave ridge building in aloft.  This weak ridge will linger into
Tuesday before the flow turns more southwesterly in advance of an
approaching trough midweek. Despite the ridging, periods of mid and
high cloud cover are likely for the early part of the week thanks to
an active Pacific flow aimed at the West Coast and the low amplitude
nature of this ridge.

Bigger changes will begin to move in as early as Tuesday evening
with increasing precipitation chances spreading into the Sierra.
Origins of the moisture source for this midweek storm system are in
the tropical Pacific, so this storm will be quite warm, limiting
snow accumulations to the highest elevations above 7-8k feet.  Model
agreement remains unclear with the timing of the best precipitation
chances, with the GFS about 12 hours faster than the ECMWF. But
general consensus is for precipitation chances to increase Wednesday
for areas north and west of I-15, and  then spread to the entire
region Wednesday night into Thursday before shifting east Thursday
night.  With these trends in mind, boosted PoPs slightly for the
above mentioned time periods, but further tweaks and enhancements
can be expected as model agreement improves over the coming days.
Improving conditions are expected Friday as the weather system
departs to our east.
&&

.AVIATION...For McCarran...Gusty south to southwest winds are
expected again today with gusts ranging 20-25 KTS. A slight chance
of showers will be possible this afternoon along with a slight
chance of thunderstorms mainly east and north of Las Vegas.

For the rest of southern Nevada, northwest Arizona and southeast
California...Gusty south to southwest winds will be seen again today
with most areas seeing wind gusts 20-25 kts. Areas generally south
of I-15 could see occasional gusts to around 30 kts this afternoon.
Isolated to scattered showers are expected mainly this afternoon
with more widespread showers developing this evening over northern
Mohave County. Thunderstorms will be possible this afternoon and
evening across mainly Lincoln and northern Mohave Counties.
&&

.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures.
&&

UPDATE...Pierce

SHORT TERM/AVIATION...Gorelow
LONG TERM.............Outler

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