Flash Flooding and Damaging Wind in Nevada, August 1, 2023

Area Forecast Discussion
National Weather Service Las Vegas NV
158 PM PDT Tue Aug 1 2023

.SYNOPSIS...Scattered thunderstorms will develop and move north
this afternoon and evening, with some persisting overnight.
Thunderstorm chances will push farther northeast Wednesday, becoming
focused in northwest Arizona and south central Nevada as drier air
spreads over southeast California. This dry air will cover the
entire region by Friday, and high pressure building overhead will
bring a return to above normal temperatures.
&&

.SHORT TERM...through Thursday night. Early afternoon loops of
satellite and area radars showed a similar situation to what
unfolded yesterday, with some crucial detail changes. Similar to
yesterday, a large area of debris clouds from overnight storms was
moving through the region, with thunderstorm development occurring
in areas which had cleared and gotten sunshine. Differently, the
clouds were over the northern half of our CWA and moving north,
versus being over the western half of our CWA and moving west
yesterday afternoon. This shows how the flow pattern has changed in
the wake of the disturbance which passed by yesterday. Surface
dewpoints were in the 50s to mid 60s over most of the CWA, and
precipitable water values were still above 1.5 inches southeast of
Interstate 15, so storms were efficient rain producers and downdraft
CAPE was limited. Wednesday, as southwest flow becomes entrenched,
lower dewpoints and more stable air will spread over southeast
California, which should limit thunderstorm chances to southern
Nevada and northwest Arizona. The drying trend will continue
northeastward Thursday, wiping out essentially all remaining PoPs.
Then, the focus will return to heat as high pressure aloft noses
back in from the southeast. The greatest effects will come in and
possibly beyond the long term period.

.LONG TERM...Friday through Tuesday.
The plume of Monsoonal moisture responsible for early week showers
and storms will lift northeastward as high pressure becomes
reestablished across the southwest U.S. This results in rather high
confidence in a return to hot and dry conditions this weekend. All
of the ensembles point to this solution, with the National Blend of
Models depicting a return of highs some 5 to 10 degrees above
seasonal normals. This would mean highs of 105 to 110 in the Vegas
Valley, and naturally hotter in our more heat-prone areas such as
Death Valley and the Colorado River Basin. Otherwise, rather benign
weather conditions are on tap with virtually no chance of meaningful
precipitation.
&&

.AVIATION...For Harry Reid...Prevailing east winds of 12kts or less
are expected at the field this afternoon.  However, thunderstorm
activity in and near the Vegas Valley will greatly influence wind
directions at the field later this afternoon and evening, with
outflow winds of 20 to 30 kts from the direction of the storms
possible.  The best time for impacts will be 22Z to 02Z, with most
of the activity tapering off by 04Z.  Light winds will return during
the overnight hours, but another area of showers and thunderstorms
will be possible on Wednesday morning, generally before noon. Dry
and warmer conditions return for the end of the week.  While smoke
from the York fire in the Mojave National Preserve has diminished,
reductions in surface and slant visibility are still possible at
times through the TAF period.

For the rest of southern Nevada, northwestern Arizona, and
southeastern California...Showers and thunderstorms are possible
across the entire area again this afternoon and evening, any of
which will be capable of producing wind gusts of 20 to 30 kts from
the direction of the parent storm.  The most like time of impacts at
the Las Vegas Valley TAF sites will be between 22Z and 02Z; between
21Z and 03Z at KBIH; Between 21Z and 01Z at KDAG; and between 21Z
and 02Z at both KEED and KIFP.  Away from convective activity,
prevailing winds will be south to southwest.  The threat of
convection will gradually decrease from south to north on Wednesday,
with only the Vegas Valley sites having a significant chance.  While
smoke from the York fire in the Mojave National Preserve has
diminished, reductions in surface and slant visibility are still
possible at times through the TAF period at the Vegas Valley sites.
&&

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

SHORT TERM...Morgan
LONG TERM...Austin
AVIATION...Planz

For more forecast information...see us on our webpage:
https://weather.gov/lasvegas or follow us on Facebook and Twitter