173
FXUS65 KVEF 181130
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
430 AM PDT Mon Aug 18 2025

.KEY MESSAGES...

* Temperatures warm through the week starting today. Increasing
  confidence for dangerous heat Wednesday through at least Saturday
  with above normal high temperatures and minimal overnight relief
  as low temperatures remain very warm.

* Moisture increase mid week with anomalous moisture over the region
  through the weekend. Precipitation chances increases through the
  week, with the highest risk for thunderstorm impacts being over
  the terrain this the weekend.

* Very dry conditions with dry low levels could result in lightning
  strikes starting wildfires.

&&

.DISCUSSION...Through Sunday.

A warming trend is expected starting today as high pressure builds
over the Four Corners region. Above normal temperatures return
Tuesday and will continue to climb to 5-7 degrees above normal
Thursday and Friday. While high temperatures will not be the most
extreme we have seen this summer, overnight temperatures will play a
role in the heat impacts as moisture could keep lows very warm. NBM
shows a 30% chance that Las Vegas, NV will not fall below 90F
Thursday night through Saturday night. Given the duration of the
heat, the above normal daytime temperatures, and the minimal
overnight relief- this yields widespread Major HeatRisk with even
some pockets in the Extreme category. Increasing moisture does
introduce some uncertainty in the temperature forecast, however NBm
shows minimal spread in high temperatures. Given all this- there is
enough confidence at this time to issue a Heat Watch for much of the
region for Wednesday through Saturday. While temperatures will begin
to cool Saturday, lows in the morning will still be warm and Heat
Risk still shows some pockets of Major Heat Risk. Can adjust timing
and areas as needed when/if the Watch is converted to a
Warning/Advisory if the temperature forecast changes.

As the area of high pressure sets up over the Four Corners, the flow
will turn south to southeast which will advect moisture into the
region. Moisture increases will start Tuesday and continue through
much of the week, however showers and thunderstorms may struggle at
first as upper level height rises could create a mid-level
subsidence inversion (which is noted on GFS forecast soundings).
This inversion slowly erodes each day starting Thursday with
precipitation chances spreading eastward as subsidence aloft wanes.
Synoptic forcing will be lacking, so daily changes in the patterns
and mesoscale features could drive convection (outside of terrain
driven development). The highest and most widespread precipitation
chances are this weekend as 150%-175% of normal PWATs set up over
the region. The finer convective details remain to be seen at this
range, all the typical monsoon hazards (flash flooding, strong
outflow winds, frequent lightning) could be in play.

Wildfires will also be a concern with convection, especially earlier
in the period. It has been a very dry summer, and brush and trees
are extremely dry. Any thunderstorm could ignite a fire via a
lightning strike outside the main rain shaft. At this time, it looks
like storms will start off as a mix of wet and dry, transitioning to
more wet fairly quickly, so the coverage of dry lightning will
likely be too low to justify Red Flag Warnings. That said, new fire
ignitions will be a concern until there has been wetting rain.

&&

.AVIATION...For Harry Reid...For the 12Z Forecast Package...Mainly
diurnal winds are expected through Tuesday morning, with light
southwesterly winds this morning gradually veering to the east,
and then to the south this afternoon. Speeds are expected to
remain 10KT or less, before winds become light after sunset. VFR
conditions prevail with an uptick in mid-level clouds around
12-15kft this evening onward. Temperatures will exceed 100F
between 21Z-03Z, topping out around 103F.


For the rest of southern Nevada, northwest Arizona and southeast
California...For the 12Z Forecast Package...Winds will follow
typical diurnal patterns across the region through the forecast
period. Speeds will be around 10KT or less, with a few exceptions.
Across the western Mojave Desert, gusty west-southwest winds will
develop by early evening, and in the Owens Valley, gusty up-
valley winds are expected this afternoon, with gusts to 25-30KT
thereafter through mid to late evening. Any gusts elsewhere will
be intermittent at best during peak heating, generally around
15-18KT at most. VFR conditions will prevail areawide, with
increasing mid-level clouds across southern Nevada and
northwestern Arizona this evening.

&&

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

&&

$$

DISCUSSION...Nickerson
AVIATION...Phillipson

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