Severe Thunderstorm Warning 20, NWS Las Vegas, NV

Area Forecast Discussion
National Weather Service Las Vegas NV
158 PM PDT Mon Jul 31 2023

.SYNOPSIS...Monsoon moisture has spread into the region, which will
result in greater thunderstorm coverage over northwest Arizona,
southern Nevada, and southeast California through Tuesday.
Thunderstorm chances will spread into south central Nevada Wednesday
before moving away to the northeast Thursday and Friday. Stronger
storms will be capable of producing heavy rain with localized flash
flooding and strong winds. Drier conditions Thursday and beyond will
allow temperatures to return to near to above normal late in the
week into the weekend.
&&

.SHORT TERM...through Wednesday night. Early afternoon satellite
loop showed very impressive mesoscale convective vortex, left over
from last night's complex that went through Yuma, spinning westward
over the northern Baja just south of Campo. This feature had brought
a roughly north-south oriented band of clouds and a few
thunderstorms which has been moving west all day, and was roughly
from Barstow through the Nevada National Security Site early this
afternoon. Farther east, where skies had cleared and abundant low
level moisture was present, thunderstorms were firing over the
mountains of Mohave, Clark, and Lincoln counties. Expect storms to
increase in coverage as the afternoon goes on, and at least some
storms should persist all night in the moist and unstable
environment. Speaking of moist, surface dewpoints in the 50s and 60s
and precipitable water as high as 1.75 inches will make flash
flooding the main threat with storms. There is some clustering among
the high resolution models showing precip in the Las Vegas Valley
Tuesday morning, which could stabilize things for the afternoon, but
confidence in this exact placement and timing is low. Regardless,
areas which don't see morning precip and/or thick cloud cover during
the day will be susceptible to thunderstorm development, with heavy
rain and flash flooding the main threat again. For Wednesday, more
stable air starts to work in from the southwest, which should reduce
thunderstorm coverage over southeast California, although southern
Nevada and northwest Arizona will likely have one more active day.
The York Fire is another issue worth discussing. As of this morning,
the fire was up to 77,000 acres, and had burned across the state
line from the Mojave National Preserve into Clark County. The fire
was producing lots of smoke, which the HRRR Smoke model expects to
continue affecting Las Vegas. The increased humidity in the area
will act to slow the fire's spread, and any rain on the fire will be
helpful. On the flip side of that coin, any thunderstorm outflow
winds could push the fire erratically, and any lightning strikes
outside of rain cores could start new fires.

.LONG TERM...Thursday through the weekend.

Southwesterly flow finally begins to scour out the monsoonal
moisture on Thursday, with PoPs largely limited to northeastern
portions of the CWA. By Friday, precip chances are pretty much gone
as the upper-level high begins to expand westward. Over the weekend,
the elongated ridge becomes centered near Yuma, placing us under
light westerly flow and anomalously high 500mb heights. The end
result of this development is dry conditions and slightly above-
normal temperatures. It's probable that these warm and dry
conditions last well into August. The latest CPC 8-14 day outlook
keeps our temperatures slightly above normal and precipitation below
normal through mid-August.
&&

.AVIATION...For Harry Reid...Easterly winds early this afternoon
will turn southeast by late afternoon, with occasional gusts to 15kt
possible after 21Z.  Scattered thunderstorms are also possible in
the vicinity of the terminal from mid-afternoon through mid-evening,
any of which will be capable of generating outflow winds to 30kts
from the direction of the storms.  A lull in the storm activity is
expected overnight, but additional storms are possible by tomorrow
afternoon.   Reduced surface and slant range visibility can be
expected through the TAF period as smoke from the York Fire in the
Mojave National Preserve continues to spread across the valley.

For the rest of southern Nevada, northwestern Arizona, and
southeastern California...Scattered thunderstorms are expected
across most of the region over the next few days, any of which will
be capable of producing gusty, erratic outflow winds.  The best
chances of storms will be near the Vegas area terminals, KDAG, and
KIFP.  Storms are also possible near KEED, but chances are a bit
lower.  Away from storms, winds will generally follow typical
diurnal trends with speeds of 15kts or less. Some reduction in
surface and slant range visibility can be expected through the TAF
period across Clark, northern Mohave, and eastern San Bernardino
counties as smoke from the York Fire in the Mojave National Preserve
continues to spread across the area.
&&

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

SHORT TERM...Morgan
LONG TERM...Woods
AVIATION...Planz

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