742
FXUS65 KVEF 200527
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
1027 PM PDT Tue Aug 19 2025

.KEY MESSAGES...

* A stretch of very hot conditions is expected beginning tomorrow
  and lasting into the upcoming weekend. Heat-related warnings
  and advisories are in place.

* A return of Monsoonal moisture will result in an increase in
  chances for showers and thunderstorms, especially over the
  higher terrain. These will bring the potential for
  strong/potentially damaging winds and heavy rains/flash
  flooding.

&&

.DISCUSSION...

Short and medium range ensemble guidance is in very good
agreement regarding a powerful Four Corners ridge of high
pressure. This feature will intensify mid to late week. Given our
abnormally dry conditions for mid-August, the subsidence
associated with this feature will result in very hot conditions
across much of the Desert Southwest. As such, Extreme Heat
Warnings and Heat Advisories remain in effect beginning tomorrow
and lasting into the weekend. With moisture set to return over the
weekend, it would make sense that temperatures may cool slightly
owing to increased cloud cover. However, as we are initially on
the gradient of moisture return, it may take a day or two to see
a response in temperatures. The increase in moisture will also
bring about muggier than usual conditions, which will make
temperatures feel hotter, and limit the potential for overnight
cooling. This will promote a prolonged risk of heat exposure,
especially for those who are sensitive to heat and/or do not have
adequate access to cooling.

The positioning of the aforementioned upper ridge will usher in a
period of optimal south/southeast mid and upper level flow. This
will finally allow meaningful moisture to return to the Desert
Southwest late this week into the weekend, with perhaps the
highest and most widespread chances for Monsoon thunderstorms we
have seen in well over a month. Given the presence of upper
ridging and large scale subsidence, conventional wisdom would
favor the mountains and nearby higher terrain for greater coverage
of showers and thunderstorms. That being said, ensemble guidance
is quite bullish,even in the lower elevations, with precipitation.
It is apparent that the ensembles may not be handling the rapid
influx of moisture all that well. While thunderstorm outflow
interactions can and do promote showers/storms in the lower
elevations, coverage is generally more isolated in nature. Without
much in the way of upper level forcing, it remains to be seen
just how widespread our afternoon showers and storms are, but it
will certainly be more active than it has in the last several
weeks. With PWAT values some 150-200% of normal, and modest
instability, the potential for locally heavy rains and flash
flooding will also exist. Initial storms late this week may also
pose a greater risk of damaging downburst winds given the extreme
heat and dry/deeply mixed environment. Stay tuned and prepare for
a return to our regularly scheduled Monsoon.

&&

.AVIATION...For Harry Reid...For the 06Z Forecast Package...Quiet
weather is expected overnight with the typical southwesterly winds.
Light winds early Wednesday morning should become easterly late in
the morning, remaining less than 10 knots outside of any sporadic
gusts as temperatures heat up. Winds should go back around to
southwesterly around sunset. High clouds will be increasing, but no
clouds expected at or below 10K feet. Temperature rising above 100F
around 19Z, peaking around 108F, then falling below 100F around 04Z.

For the rest of southern Nevada, northwest Arizona and southeast
California...For the 06Z Forecast Package...Generally quiet weather
is expected through Wednesday evening, with wind gusts of 20 knots
or less following typical day/night directional patterns. High
clouds will increase from south to north, but no clouds expected at
or below 12K feet MSL.
&&

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

&&

$$

DISCUSSION...Austin
AVIATION...Morgan

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