Flash Flood Warning 11, NWS Las Vegas, NV

Area Forecast Discussion
National Weather Service Las Vegas NV
1242 PM PDT Mon Jul 15 2024

.SYNOPSIS...Scattered monsoon activity today, with rain chances
largely confined to our eastern areas tomorrow through Wednesday.
Later in the week, temperatures rise and precipitation chances
expand westward as high pressure builds in from the east.

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.SHORT TERM...through Wednesday.

Shower and thunderstorm development is anticipated once again this
afternoon as monsoonal moisture lingers. Best chances (40-70%) are
along and south of I-15 where the better moisture is, but 25-40%
PoPs exist from northwestern Inyo County over to northern Lincoln
County. The I-15 corridor and points south also have the best odds
of seeing localized flash flooding, with the WPC giving this area at
least a 5% chance of excessive rainfall. Based on mean flow within
the cloud layer, most concerned with the Twentynine Palms area, the
Mojave Preserve up into the southern McCullough Range, and the
northern Hualapai Mtns up towards Hackberry and Valentine.
Yesterday, we saw rain rates of 1-3" per hour, and I wouldn't
discount the potential to see similar rates today. By 7-8PM this
evening, convective activity is expected to cease as daytime heat is
lost.

For Tuesday and Wednesday, the development of a westerly component
in the flow will shunt some of the low-level moisture off to the
east. As a result, the best rain/storm chances move into
northwestern Arizona and eastern Lincoln County. Elsewhere, PoPs
remain below 20% due to the drier air. This also allows temperatures
to climb a few degrees, placing much of the Mojave Desert in the 100-
115 range and the southern Great Basin in the 90-105 range. Despite
the slight increase in temps, HeatRisk remains in the Moderate
category.

.LONG TERM...Thursday through the weekend.

Later in the week, the Four Corners high strengths and slowly
retrogrades. SSE flow due to the anticyclonic circulation brings
moisture westward while the rising 500mb heights induce additional
warming. Because the moisture never truly leaves the region earlier
in the week, it gets trapped underneath the high. The end result is
the return of Major HeatRisk to most of our Mojave Desert valleys by
Friday and the weekend, all while PoPs gradually expand west and
increase. This creates a fair amount of uncertainty in the forecast,
particularly the temperature forecast, as any afternoon convection
or convective cloud debris will limit afternoon heating. However, if
temperatures aloft suppress, or mostly suppress, shower/storm
activity, it'll likely be hot with more humidity than usual.

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.AVIATION...For Harry Reid...Generally light winds favoring an
easterly direction this afternoon, outside of outflow from
convection, with some variability in the easterly wind direction.
Scattered storms initially developing over the higher terrain
surrounding the valley. There is a 30% to 40% chance of storms
moving off the terrain and directly impacting the field. Outside of
direct impacts from storms in the valley, outflow winds from nearby
storms could bring periods of gusty, erratic winds to the terminal
area. Storms should end by early evening with light westerly winds
expected after sunset. Isolated storms are possible again late
morning and afternoon on Tuesday, but the majority of the activity
should be confined to northwest Arizona.

For the rest of southern Nevada, northwest Arizona and southeast
California...Scattered thunderstorms will continue to develop across
much of the region this afternoon and persist through sunset before
decreasing. Storms will be capable of producing lightning, brief
periods of heavy rainfall, CIGs less than 10kft that could obscure
areas of higher terrain, and sudden gusty outflow winds.  Away from
areas of convection, south-to-west winds at 10kts to 15kts with
occasional gusts to 20kts are expected. The thunderstorm activity
should diminish after sunset, with winds falling below 10kts in most
areas overnight. Additional thunderstorms are possible on Tuesday,
but coverage is expected to be more limited, with the majority of
the activity remaining over northwest Arizona and the higher terrain
north and west of the Las Vegas Valley.

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

&&

DISCUSSION...Woods
AVIATION...Salmen

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