FXUS65 KVEF 202057

Area Forecast Discussion
National Weather Service Las Vegas NV
157 PM PDT Tue Mar 20 2018

.SYNOPSIS...A Pacific storm system will bring mostly cloudy skies
through Thursday. Rain chances will begin in Inyo County this
evening, spread to areas north and west of Interstate 15 Wednesday,
and areawide Thursday. Heavy rain is most likely in Inyo County,
with the heaviest snow near and above 10,000 feet. Clouds will begin
to clear on Friday, with dry weather expected for the vast majority
of the area Saturday through Tuesday.

.SHORT TERM...through Thursday night. Almost everything still looks
on track for the upcoming storm. Still expecting the greatest
rainfall amounts over Inyo County, particularly the Sierra, Owens
Valley, and White Mountains, so hoisted a Flood Watch beginning at 2
PM tomorrow afternoon. Any snowpack below about 10,000 feet could
also add to the runoff as the warm rain washes it away. As snow
levels fall in the Sierra Thursday, the rain will change to snow,
but it is questionable how efficiently the snow will accumulate
after two to three inches of rain has fallen. Chose to err on the
side of caution and issued a Winter Weather Advisory above 7000 feet
beginning at 11 AM Thursday. Elsewhere, the main change was to slow
down the onset of precip chances even further. Models are still
persistently different with timing, and tried to move closer to a
middle ground. Still expecting the best precip chances to reach Las
Vegas on Thursday, with amounts only around a quarter of an inch. An
inch or so of rain is probable in the Spring Mountains, with snow
confined to the highest peaks. By Thursday night, the main moisture
plume will be swinging east, and precip chances and amounts will
start to decrease from west to east.

.LONG TERM...Friday through Tuesday.

Over the past 24 hours, models have trended drier and weaker with
the upcoming storm system. By Friday, much of what is left of the
moisture plume will be north and east of the area. Models still
indicate a weak shortwave will move across the area early Friday but
they differ on the strength of this feature. Since inconsistencies
exist decided to go with slight chances mainly north of Clark County
and the Mojave Preserve area, with better chances across the Arizona
Strip. By Friday afternoon/evening dry southwest flow ahead of a
broad upper low will move over the area pushing the moisture
eastward and bringing breezy to gusty southwest winds. Both the
GFS/ECMWF have some sort of shortwave energy pushing into northern
California and the Great Basin Saturday-Sunday, but the timing,
location, and intensity of this feature remains uncertain.
Generally, with limited moisture the only potential impacts looks
like increased SW winds mainly SAT. Beyond Saturday confidence is
low as models become vastly different. Temperatures will run about 4-
9 degrees below normal with mostly clear skies beginning Friday
afternoon continuing through much of the weekend and into early next

.AVIATION...For McCarran...BKN to OVC VFR clouds the rest of the
afternoon with light winds favoring the east. Winds will then veer
southwest after sunset. Wednesday morning, confidence in the
forecast decreases. Winds should continue to favor the southwest
however how strong winds will become and when they will increase is
uncertain. Confidence for breezy winds increases after 19Z as more
models highlight wind gusts out of the southwest. In addition to the
winds, watching the potential for some lower clouds around 6000ft
Wednesday afternoon. Not enough confidence to include a BKN deck at
this time, but may need to be added with later updates.

For the rest of southern Nevada, northwest Arizona and southeast
California...Light rain showers and virga over the Sierra this
afternoon will spread eastward across the Western Mojave Desert and
southern Great Basin this evening and overnight. Otherwise, BKN to
OVC skies are expected through Wednesday, with lowering CIGs
expected in any showers. Winds will be light and favor diurnal
trends for most TAF sites.

.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures. Rainfall and flooding reports are encouraged during
periods of weather later this week.


LONG TERM...Kryston

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