Severe Thunderstorm Warning 19, NWS Las Vegas, NV

Area Forecast Discussion
National Weather Service Las Vegas NV
1242 PM PDT Fri Aug 2 2024

.SYNOPSIS...Scattered showers and storms today as a monsoonal system
moves through the area. Convective activity becomes more isolated
this weekend and into next week as high pressure builds in.
Temperatures rise to dangerous levels by Sunday and continue through
at least Tuesday as Major to Extreme HeatRisk return to the Mojave
Desert.

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.SHORT TERM...Today and Saturday.

A ragged band of light rain persists from Death Valley and the
southern Owens Valley to west-central Mohave County as the invert
trough lifts north. Abundant mid-level and high clouds ahead of the
trough axis is slowing diurnal heating across our northern areas,
which will delay convective initiation in these locations until the
late afternoon. Farther south, convection is expected to be more
isolated and primarily concentrated in two area. These areas are
western San Bernardino County (from Twentynine Palms up towards
Ridgecrest) and eastern Mohave County (especially the AZ Strip).
Latest satellite imagery already shows agitate cumulus in these
locations, suggesting that the atmosphere has already begun to
destabilize. The deeper convection that develops today will pose the
typical monsoon hazards (localized flash flooding, gusty outflow
winds, and lightning). Here in the Vegas area, clouds are still
holding firm with the aforementioned band of showers to our south
and high cirrus from the trough's forcing. This has kept our
temperatures in check (only up to 100 degrees as of noon) and
hindered our chances of deep convection today. It is worth noting
that our current temperature is a bit warmer than what most CAMs
expected at this time, so we may destabilize slightly more than
modeled. However, updrafts will also be fighting larger-scale
subsidence behind the trough axis. As such, rain chances in the
valley remain low (10-15%), with better odds on the Spring Mountains
(20-40%). If the valley sees any precipitation, it'll most likely
come between 1-3 PM from the shower activity to our south.

Tomorrow, guidance is in good agreement that moisture will decrease
across the area. With no trough to aid in storm development,
convection will largely be confined to eastern Mohave County, with
low chances (~20%) existing on the Sierra and Spring Mountains. The
limited convection and clouds cover tomorrow will also allow
temperatures to warm 3-5 degrees more than today, with the warming
trend continuing into next week.

.LONG TERM...Sunday through Thursday.

The Four Corners 500mb high begins to build westward on Sunday,
becoming positioned over our CWA by mid-week. Combined with
decreased convective activity, this causes our temperatures to climb
5-10 degrees above normal across the area. While moisture is
expected to decrease from Friday/Saturday values, PWATs remain
around 1" here in Vegas through at least Tuesday. This moisture will
keep lows well above normal, limiting overnight heat relief and
producing Major to Extreme HeatRisk over much of the Mojave Desert.
Thus, an Excessive Heat Watch has been issued for Sunday through
Tuesday for most of Clark, Mohave, and San Bernardino Counties, as
well as Death Valley and southern Nye County. The decreased but
still slightly above climatological moisture will allow PoPs to
linger in parts of the area. Best chances for shower/storm activity
are in central and eastern Mohave County, where the NBM paints 25-
50% PoPs each afternoon. Farther west, PoPs of 10-20% are generally
confined to the Spring Mountains and Mojave Preserve.

For Wednesday and beyond, the temperature forecast becomes more
uncertain as some guidance suggests moisture will begin to increase
with the arrival of another inverted trough while other guidance
shows a more persistent ridge and PWAT values. The former scenario
would yield cooler temps and high rain chances, while the latter
would likely yield a continuation of excessive heat.

&&

.AVIATION...For Harry Reid...Easterly winds of less than 10kts will
continue into the early afternoon before gradually transitioning to
the southeast by mid-afternoon and eventually to southwest-to-west
this evening.  While VCSH has been removed from the latest TAFs, an
isolated shower or thunderstorm can not be completely ruled out
between 20Z and 00Z.  If any were to occur, they would likely remain
over or near the higher terrain surrounding the valley. Winds
overnight will remain less than 8kts.  Mid- and high-level clouds
will continue to move across the area through tonight, although
bases are expected to remain 10kft AGL or higher.

For the rest of southern Nevada, northwest Arizona and southeast
California...Areas of showers and embedded thunderstorms will
continue to move northwest across eastern California and southern
Nevada this afternoon.  A few thunderstorms can also be expected in
areas that have seen clearing today, including near KDAG and areas
well north and east of the Vegas Valley.  The main concerns from any
storms are gusty and erratic winds and locally heavy rainfall,
resulting in reduced visibility.  Away from shower and thunderstorm
activity, winds are expected to remain 10kts or less through
tonight.  Mid- and high-level clouds will continue to move across
the area through tonight, although bases are expected to remain
10kft AGL or higher and will not cause significant disruptions.

&&

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

&&

DISCUSSION...Woods
AVIATION...Planz

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