Excessive Heat in California, August 20 to 23, 2025

Area Forecast Discussion
National Weather Service Las Vegas NV
448 AM PDT Wed Aug 20 2025

.KEY MESSAGES...

* Extreme Heat Warnings and Heat Advisories will go into effect
  this morning, continuing through Saturday as hotter than normal
  temperatures stick around through the end of the week.

* Monsoonal moisture will return to the Southwestern US, bringing
  increased chances for afternoon showers and thunderstorms as we
  head into the weekend. Lightning, strong outflow winds, and
  heavy rain capable of resulting flash flooding will be potential
  hazards with these storms.

&&

.DISCUSSION...through next Wednesday.

Temperatures will continue to heat up through the end of the work
week as we find ourselves under a ridge of high pressure centered
over the Four Corners region. As we continue to heat up, we will see
high temperatures top out around 4 to 8 degrees above normal by the
end of the week. In addition to afternoon temperatures being hotter
than normal, there will be little relief in the form of overnight
low temperatures as those will be around 5 to 12 degrees above
normal later this week. These warmer than normal overnight
temperatures combined with hotter than normal afternoon high
temperatures will quickly drive HeatRisk up across southern Nevada,
northwestern Arizona, and southeastern California. Furthermore, with
the ridge centered over the Four Corners, we will see monsoonal
moisture increase across the region. This will make things feel
muggier than normal, especially given how dry this summer has been.

Speaking of the return of monsoonal moisture, we will begin to see
chances for showers and thunderstorms creep into the eastern portions
of our forecast area on Thursday afternoon. Chances for afternoon
convection will become more widespread on Friday and Saturday with
precipitation chances hanging around into next week. Strong outflow
winds, localized heavy rain capable of resulting in flash flooding,
and lightning will be threats with any storms that develop during
the second half of the week. The monsoonal moisture will stick
around into next week, recirculating beneath the ridge. Despite the
presence of anomalous moisture, confidence in anything beyond
shallow terrain based convection is low due to the subsidence
beneath the ridge. However, mesoscale phenomena such as an MCV or
sufficiently strong outflow winds could help with additional
convective development.

&&

.AVIATION...For Harry Reid...For the 12Z Forecast Package...Winds
will generally follow diurnal patterns, similar to previous days.
Variable winds this morning will veer and settle out of the east
and southeast this afternoon, before shifting to the southwest
this evening. Sustained speeds are expected to remain 10KT or
less, with minimal chances for higher gusts. VFR conditions
prevail through the forecast period, with increasing mid-level and
high clouds, especially this evening onward. Temperatures today
will exceed 100F between 18Z-05Z, with a high of 108F around 00Z.

For the rest of southern Nevada, northwest Arizona and southeast
California...For the 12Z Forecast Package...Winds across the
region will generally follow diurnal patterns, with speeds
remaining around 10KT or less through the forecast period.
Exceptions are across the Owens Valley, where gusty up-valley
winds to 20-25KT are expected to develop this afternoon, and
across the western Mojave, where a period of elevated and
intermittently gusty westerly winds is expected this evening into
tonight. Otherwise, VFR conditions prevail with increasing mid and
high clouds through tonight.

&&

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

&&

DISCUSSION...Stessman
AVIATION...Phillipson

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