Winter Storm Watch 3, NWS Las Vegas, NV

Area Forecast Discussion
National Weather Service Las Vegas NV
759 PM PST Mon Nov 13 2017

.SYNOPSIS...Periods of high clouds can be expected the next couple
days, along with near normal temperatures. On Wednesday and
Thursday, a weather system will bring rain and mountain snow to the
Owens Valley and Sierra Slopes. Elsewhere, dry conditions but
increased breezes and cloud cover are likely. Things dry out over
the weekend but an additional weather system may move into the
region by early next week.

&&

.UPDATE...Stream of high level tied to the tropics which
overspread the region Sunday looks to continue for the next several
days. RH progs and time height for Las Vegas indicate RH values
between 60-100 pct between H5-H3 through Wednesday morning. Updated
sky grids to increase coverage of clouds a bit more for Tuesday. No
other changes.
&&

.PREV DISCUSSION...145 PM PST Mon Nov 13 2017
.SHORT TERM...Through Tuesday night.

Much like yesterday, widespread cirrus has hindered the daytime
heating cycle with temperatures struggling to rise through the
morning hours across the southern two-thirds of the forecast area.
These clouds are likely to persist through sunset, so observed highs
today may again be a bit shy of forecast.  Another day of widespread
clouds are on tap for Tuesday, so I undercut guidance slightly to
match what we've been observing the past couple of days.  Otherwise,
aside from somewhat gloomy skies, fair weather is expected with
light winds.

LONG TERM...Wednesday through Sunday.

Still on track for a decent precipitation event across the Sierra
Wednesday evening into Thursday. This will be the result of a
Pacific trough pushing through the PacNW and Great Basin, dragging a
decaying frontal band and associated precipitation shield southward.
Most of the heaviest precipitation will be intercepted by the Sierra
crest, but some spillover is still likely into the Owens Valley,
especially Thursday morning.  In the higher terrain of the Sierra,
particularly above 8,000 feet, several inches of snow accumulation
are likely, with amounts over a foot possible above 10,000 feet.

In addition to the precipitation, downslope winds are possible in
the Owens Valley Wednesday before precipitation materializes over
the Crest. Strong gusts to 60 mph are possible in localized spots,
mainly west of US-395.  Cross sections from the Owens Valley do
suggest a decent downslope event is possible, and I considered
issuing a high wind watch, but will let the midnight shift give it
another look before pulling the trigger.

Outside of the Sierra and Owens Valley, relatively minimal impacts
are expected by this midweek storm aside from breezy conditions and
additional cloud cover. Temperatures will cool area wide Friday into
the weekend, with the coolest night of the year so far possible
Friday night into Saturday as the post frontal airmass settles over
the region.  While significant uncertainty remains, early
indications are for another weather system to arrive early next
week, possibly bringing renewed precipitation chances to much of the
area.

&&

.AVIATION...For McCarran...Light winds under 8 kts will favor
typical diurnal trends through Tuesday. Abundant high level clouds
are expected through Tuesday with bases at or above 20 kft.

For the rest of southern Nevada, northwest Arizona and southeast
California...Winds of 10 kts or less are expected over much of the
region through Tuesday and will mainly favor typical diurnal trends.
The exception will be the Sierra and western San Bernardino County
where some stronger westerly winds are possible tonight and early
Tuesday. Abundant high level clouds can be expected through Tuesday
with bases mainly above 20 kft.

&&

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

Update...Pierce

DISCUSSION...Outler
AVIATION...Harrison

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