Flash Flooding and Dust Storm in Arizona, July 7 to 9, 2018

Area Forecast Discussion
National Weather Service Las Vegas NV
130 PM PDT Sat Jul 7 2018

.SYNOPSIS...Hot temperatures are expected through the weekend
along with near daily chances for thunderstorm activity. The highest
chances for storms will be across the high terrain of Mohave, Clark,
and San Bernardino counties. Moisture will continue to slowly seep
north and west through next week bringing daily chances for showers
and storms.
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.SHORT TERM...Through Sunday Night.

Widespread debris clouds this morning have limited afternoon
convection across much of the region today.  The exception has been
on the edges of the cloud shield where a few storms have formed over
the Spring Mountains and far Southeastern Inyo county.  Weak shear
and limited buoyancy has kept the storms fairly weak overall, though
some heavy rain of up to a half an inch has been observed.  A few
additional storms may form later this afternoon, especially in
places which saw full sunshine today, but overall, relatively low
thunderstorm coverage is expected.

Another day of activity is expected Sunday, which could prove more
robust than today given a sunnier start to the day expected with
similar atmospheric moisture content. Early runs of the HRRRx
suggest activity first developing across Mohave county and pushing
west in the afternoon and evening, with additional storms possible
near the Colorado river and Southern Nevada.  This scenario seems
reasonable but we will continue to monitor trends.

Aside from the moisture, very hot temperatures will continue across
our western zones with temperatures above 100F on most of the valley
floors, with Death Valley rising up above 120F. Slightly cooler
conditions are expected further east thanks to increased moisture
and thunderstorm activity.

.LONG TERM...Monday through Friday.

Looking out further, there are two items of note. One is a potential
increase in moisture (potentially PW values of 1.50-2.00 inches)
from late Monday through late in the week. And two, an easterly wave
that could help to generate and organize convection in the late
Monday-Tuesday timeframe. Confidence in any details beyond Monday is
low (typical for the monsoon season). However, precipitation chances
were generally increased for all time periods due to good agreement
in sustained moderate to high-grade monsoon moisture.
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.AVIATION...For McCarran...Widespread clouds this morning has
limited thunderstorm activity this afternoon. As such, I dont expect
much thunderstorm activity in the valley, though storms may impact
regional approach corridors at times.  Light south winds of 5-10
knots are likely though late tonight, though outflow from the west
or northwest is possible later this afternoon with gusts to 20 knots
possible if it materializes.  Diurnal winds expected tomorrow with
Thunderstorms possible again during the late afternoon or evening.

For the rest of southern Nevada, northwest Arizona and southeast
California...Scattered showers and thunderstorms possible this
evening mainly across the higher terrain of Inyo county and Southern
Nevada. A few storms may also form this afternoon near KDAG and KNXP
with brief downpours and gusty winds. Generally diurnal winds are
expected through the period with additional thunderstorm activity
likely tomorrow afternoon, particularly east of a KDAG to KTPH line.

&&

.SPOTTER INFORMATION STATEMENT...Monsoon season is underway across
the region. There will be chances for thunderstorms each day
through the next week. Spotter activation may be needed at times.
Regardless of activation, spotters are encouraged to report any
significant weather or impacts according to standard operating
procedures.
&&

SHORT TERM/AVIATION...Outler
LONG TERM...Wolcott

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LAS VEGAS NV
433 PM PDT SAT JUL 7 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0319 PM     FLASH FLOOD      1 W JOSHUA TREE         34.14N 116.33W
07/07/2018                   SAN BERNARDINO     CA   LAW ENFORCEMENT

            CHP ADVISED HEAVY RAIN CAUSING FLOODING
            ACROSS HIGHWAY 62.

0240 PM     HEAVY RAIN       5 SE YERMO              34.85N 116.77W
07/07/2018  M0.38 INCH       SAN BERNARDINO     CA   TRAINED SPOTTER

            TRAINED SPOTTER REPORTED HEAVY AND MINOR
            ROADWAY FLOODING.

0233 PM     FLASH FLOOD      3 SSE YERMO             34.86N 116.80W
07/07/2018                   SAN BERNARDINO     CA   LAW ENFORCEMENT

            CHP RECEIVED A REPORT OF ROADWAY FLOODING AT
            NATIONAL TRAILS HIGHWAY AND DAGGETT AIRPORT
            RD.

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