Winter Storm Warning 12, NWS Las Vegas, NV

Area Forecast Discussion
National Weather Service Las Vegas NV
152 AM PDT Mon Mar 20 2023

.SYNOPSIS...Light rain, snow showers and even a few
thunderstorms will occur across the southeastern Great Basin and
eastern Mojave Desert today. A stronger, colder system will bring
heavier precipitation, lower snow levels and gusty winds to the
region Tuesday and Wednesday. Cool and unsettled weather will
continue into next weekend.
&&

.SHORT TERM...Through Wednesday night.

Mostly cloudy skies blanketing the region this morning. Next
shortwave along the Oregon/northern CA coast producing rain/snow and
even a few thunderstorms generally along and north of Highway 50/I-
80 corridor. Trough progged to move east across northern Nevada this
afternoon. Hi-res simulations continue to support best chance for
showers will be over Lincoln County, northern Clark and northern
Mohave counties. Steepening lapse rates under cold air aloft will
support some thunderstorms. The Mojave Desert and northwest Arizona
will feel those south-southwest winds increase with gusts
approaching 40 mph.

Forecast becomes quite complex on Tuesday through Wednesday as a
much more dynamic and colder trough moves across the area. Will
probably see some snow down to 3500-4000 feet Wednesday morning but
most impactful accumulations will most likely occur above 5500 feet
so our current Winter Storm Watches will be upgraded to Winter Storm
Warnings. Heaviest snow will fall on Tuesday with additional lighter
accumulations lasting through Wednesday. Potential strong downslope
winds off the eastern edge of the San Bernardino County Mountains
and higher terrain of JTNP still looking favorable. NBM
probabilities for wind gusts >48 kts running between 60%-70% for
Twentynine Palms MCAS (KNXP). Will be issuing a High Wind Warning
for the Morongo Basin from Tuesday morning through Wednesday evening
to cover that potential. Gusty winds are forecast for the remainder
of the Mojave Desert and northwest Arizona so will blanket those
areas with a wind advisory which will running through Wednesday
morning. Finally, core of atmospheric river still slated to move
inland across southeast CA, northern Baja and into Arizona
Tuesday/Tuesday night. However, as winds aloft back ahead of
incoming trough some of that moisture gets pulled northward over
eastern San Bernardino, eastern Clark and western Arizona. QPF
forecast for southeast Mohave County continues to increase with WPC
keeping their Marginal Day 2 Excessive Rain Outlook contour across
southern Mohave County. Going to issue a Flood Watch for that area
as it won't take much rain to cause rises in rivers, washes and
other drainages due to our moist antecedent conditions.

If we can get some breaks in the clouds today, temperatures won't to
too cool for the first day Spring. Colder air with the trough on
Tuesday and Wednesday will have our highs closer to our normal lows
than normal highs. For Vegas, our normal low is 52 right now, normal
high 73.

.LONG TERM...Thursday through next Monday.

The pattern will remain rather active during the longer term period,
though significant uncertainty remains with the details.  Our wet
storm system anticipated earlier in the week will begin departing
the area Thursday with shortwave ridging building in behind it. This
should encourage drier conditions Thursday aside from some isolated
diurnal showers in the higher terrain. However, temperatures will
remain quite cool by early Spring standards.

Thereafter, a fairly large and broad, but low amplitude trough will
exist across much of the CONUS through the weekend, which degrades
forecast confidence in the details considerably as lower amplitude
patterns are typically more difficult for our extended range model
guidance to resolve. Cluster guidance offers various solutions which
mainly differ on the timing and locations of the more dominant
troughs. What we can say with confidence is that temperatures will
remain much cooler than normal with continued rounds of unsettled
weather likely to persist for the remainder of the month.
&&

.HYDROLOGY...Minor-to-moderate flooding from higher-than-normal
streamflows are forecast to continue within the Meadow Valley Wash
through the week due to recent rain, regional snowmelt, and
controlled releases from the Eagle Valley Dam in preparation for
this week's storm system. Forecast precipitation across the southern
Great Basin next week will only act to exacerbate the ongoing
flooding in Lincoln County.
&&

.AVIATION...For Harry Reid...Light and variable winds continue
through the mid-morning hours as sky conditions improve. Southwest
winds pick up in the late morning, with gusts around 25 knots
throughout the afternoon. Scattered clouds between 7-9kft, broken at
15kft. Southwest breezes weaken after sunset, but speeds remain near
10 knots. A more impressive surge of moisture arrives early Tuesday
morning, bringing low CIGs and rain. CIGs may get as low as 1-2kft
Tuesday morning, especially during precipitation. Steady, widespread
rain should keep the southwest winds in check, at 5-10 knots.

For the rest of southern Nevada, northwest Arizona and southeast
California...For the Las Vegas Valley sites, breezy southwest winds
begin in the late morning hours, continuing through the afternoon.
Gusts between 20-25 knots expected. Scattered clouds between 7-9kft,
broken at 15kft. Winds weaken around sunset, but remain from the
south-southwest. At KBIH, light north-northwest winds prevail
through the TAF period, with speeds 5-10 knots. Few clouds between 8-
10kft this afternoon, becoming widespread in the evening. At KDAG,
west winds gradually increase throughout the morning, peaking in the
afternoon around 20-25 knots. Speeds decrease after sunset to 12-18
knots. Scattered clouds between 9-12kft, with low ceilings
developing around midnight and precipitation moves in. For the
Colorado River Valley sites, light southerly breezes persist through
the TAF period with SCT-BKN clouds near 8-10kft. Precipitation and
low CIGs spread north and east to all sites by 10z-12z Tuesday.
&&

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

SHORT TERM/HYDROLOGY...Pierce
LONG TERM...Outler
AVIATION...Woods

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