FXUS65 KVEF 172055
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
155 PM PDT Wed Jul 17 2024

.SYNOPSIS...High pressure to the east will move overhead by the
weekend resulting in excessively hot temperatures and increasing
Heat Risk. Isolated to scattered thunderstorm activity will remain
possible each day with the best storm coverage expected across
northwest Arizona. A deeper push of moisture into the area next
week could bring higher storm chances while well above normal
temperatures could extend excessively hot conditions through the
middle of the week.

&&

.DISCUSSION...Thursday and Friday.

No changes were made to the Excessive Heat Watch in place for
Friday and the weekend.

Monsoon moisture increases on Thursday becoming more widespread
with precipitable water values between 130% and 180% of normal for
this time of year. Much of the region is forecast to be weakly
unstable due both to the increasing daytime temperatures and to
the moisture increase. Higher instability is forecast over the
central and southern portions of Mohave County, the Colorado River
Valley, and the far southern portions of San Bernardino County
where the HREF gives a increasing probability of CAPE exceeding
500 j/kg in the afternoon. The WPC day 2 outlook for excessive
rainfall captures much of Mohave County with the exception of the
southwest portion of the county. These areas will have the
highest potential for localized flash flooding on Thursday.

Moisture becomes trapped under high pressure that is forecast to
move over the area on Friday. Isolated to scattered thunderstorms
are forecast to continue across portions of Lincoln, Clark,
Mohave, and eastern San Bernardino counties where conditions are
forecast to be more unstable. Thunderstorm development in our
western areas will need to rely on daytime heating and topographic
lift in absence of any other lifting mechanism. Our western
valley locations are likely to have little to no convection Friday
with storms tied to the higher terrain.

Otherwise, expect generally light winds with afternoon breezes
both days and temperatures around 5 degrees above normal. An
Excessive Heat Watch goes into effect on Friday across our
southern/southeastern areas where we could see localized major
Heat Risk.

Saturday and Sunday...

The Excessive Heat Watch expands to include much of the area over
the weekend. High pressure settles over the area resulting in
more widespread major to extreme Heat Risk this weekend. High
temperatures are forecast to be around 2-3 degrees warmer while
overnight lows will be warmer overall, providing less overnight
relief from the heat.

The high will trap moisture beneath it leading to a chance of
thunderstorms each day. Warmer temperatures aloft that are
associated with high pressure will initially cap convection until
daytime heating and topographic lift work to allow storms to
develop over the mountains. Eventually, storms will roll off the
higher terrain into the valleys. Better chances for storms will
continue over our central and eastern areas while limited
convection is forecast in our western areas where more stable
conditions are expected.

Monday through Wednesday...

Temperatures are forecast to remain hot with areas of major to
extreme Heat Risk continuing. It's likely that heat products will
be needed for this period how that will look is the question.
Ensemble systems are forecasting an increase in moisture and
thunderstorm coverage early in the week which could help mitigate
the impacts from Heat Risk. In general, areas south of the I-15
drop back into the widespread moderate Heat Risk category Monday
through Wednesday with major Heat Risk more localized. Major to
extreme Heat Risk continues for areas north of the I-15 including
the Las Vegas Valley. More detailed information regarding heat
risk for the upcoming week will provided in the days ahead.

Regarding monsoon activity, low grade recycling of thunderstorms
is expected with daily storm activity forecast to be fairly
widespread.

&&

.AVIATION...For Harry Reid...Winds will be a headache this evening.
There are three possibilities: easterly outflow winds from
thunderstorms in Arizona, strong south to southwest outflow winds
from thunderstorms in extreme southern Nevada, and light easterly
winds shifting to light southerly with no outflow influence. There
is also a very low (10%) chance of these outflow winds kicking off
thunderstorm development near the terminal this evening. Thursday is
likely to be similar, with thunderstorms over the mountains in the
approach corridors and a low (20%) chance of a thunderstorm at the
terminal.

For the rest of southern Nevada, northwest Arizona and southeast
California...Expect a slight uptick in thunderstorm coverage this
afternoon versus yesterday, with the highest chances (40-50%) in
Mohave County. Storms here are likely to produce outflow winds
moving west, possibly into San Bernardino and Clark counties.
Thunderstorm chances will increase and expand across much of the
Mojave Desert and southern Great Basin Thursday, with the main
concerns again being erratic, gusty winds as well as low ceilings
and terrain obscuration.

&&

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

&&

$$

DISCUSSION...Salmen
AVIATION...Morgan

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