A little monsoon moisture crept in under the big ridge aloft responsible for the ongoing heat wave, triggering a few thunderstorms over Mohave County. Isolated severe wind and flash flooding occurred.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS VEF wrote it up.
A little monsoon moisture crept in under the big ridge aloft responsible for the ongoing heat wave, triggering a few thunderstorms over Mohave County. Isolated severe wind and flash flooding occurred.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Las Vegas, NV wrote its last area forecast discussion before the first event at Aug 18, 2:00 PM MST, 4 hours earlier.
Area Forecast Discussion
National Weather Service Las Vegas NV
200 PM PDT Tue Aug 18 2020
.SYNOPSIS...Excessive heat will last through much of the week
with continued record temperatures. Isolated thunderstorms will
continue into the evening across northwest Arizona and parts of the
Mojave Desert and drift gradually westward while accompanied by
strong wind gusts. A very slight lowering of temperatures is
expected late in the weekend into early next week as high pressure
shifts slightly eastward.
&&
.DISCUSSION...tonight through Tuesday.
Tonight...Convection has started firing over the higher terrain of
the southern Great Basin and Mojave Desert. Look for storms to move
off the higher terrain and into the nearby valleys, i.e Owens Valley
and Morongo Basin/Barstow. HRRR has been consistent in showing
convection propagating west-southwest across southern Mohave County
and into the lower Colorado River late this afternoon, between 5 and
7 pm. Primary concern will be gusty winds as forecast soundings
depict Invert-V profiles with plenty of DCAPE. Localized heavy
rain/hail possible under stronger cores as well but storm motion
should inhibit the threat of flooding. HRRR, as well as other HREF
members indicate convection will dissipate by late evening. Outside
of smoke/haze from nearby fires skies will be mostly clear to partly
cloudy overnight.
Wednesday-Tuesday...The anomalously massive ridge is forecast to
slip southeast and weaken by just a tad by the weekend. Instead of
of H5 heights hovering between 597-600 dm they will dip to between
591-594 dm. Bottom line, this will keep temperatures running well
above normal going into the weekend and the start of next week. The
Las Vegas high temperature is not forecast to be below 110 degrees
until Sunday. Numerous daily record highs/high minimum temperatures
will continue to be broken/tied along with record consecutive days
of highs above a specific temperature. Will keep our heat product
going through Thursday with option to extend in the the coming
shifts.
Isolated thunderstorms remain possible for the region Wednesday and
Thursday, specifically favoring the higher terrain. As the high
slowly shifts off to our southeast models indicate drier and more
stable air wrapping into the western periphery of the high leading
to the removal of thunderstorm potential over the southern Sierra
Nevada and central Nevada Friday and Saturday. More uncertainty
creeps into the convective potential Sunday into early next week
with just how much moisture may creep into the region as Hurricane
Genevieve brushes the southern tip of the Baja Peninsula.
&&
.FIRE WEATHER...Hot temperatures with light terrain-driven winds are
expected through the week. Near daily chances for isolated
thunderstorms can be anticipated, particularly across the Mojave
Desert and Sierra regions through Thursday. Storms will be capable
of producing strong outflow winds which may aggravate ongoing fire
activity and increase the rate of spread of new fire starts.
&&
.CLIMATE...
DAILY RECORD HIGH MAXIMUM TEMPERATURES
TUE 8/18 WED 8/19 THU 8/20
Las Vegas, NV 111 (1992)* 111 (1992)* 110 (1950)*
Bishop, CA 105 (2001)* 106 (1950) 105 (2015)
Barstow, CA 111 (1992)* 111 (2018)* 109 (2018)*
Needles, CA 115 (2015)* 117 (2018)* 120 (1919)
Kingman, AZ 109 (1915)* 111 (1915) 107 (1915)*
Death Valley 125 (2001)* 124 (1992)* 126 (1931)
DAILY RECORD HIGH MINIMUM TEMPERATURES
TUE 8/18 WED 8/19 THU 8/20
Las Vegas, NV 86 (2018)* 90 (2018)* 89 (2018)*
Bishop, CA 67 (1970) 67 (1961) 65 (1997)
Barstow, CA 80 (2001)* 80 (1973)* 82 (1973)*
Needles, CA 91 (2018)* 93 (2018)* 95 (2018)
Kingman, AZ 80 (2001) 76 (1999)* 80 (2001)
Death Valley 98 (2013)* 99 (2003)* 99 (2018)*
*-Current forecast may be close to current record values.
&&
.AVIATION...For McCarran...Storms south of the valley will likely
create outflow, arriving as southerly winds across valley this this
evening. Winds will then favor typical drainage trends later tonight
with light and variable to easterly winds to start tomorrow. By
Wednesday afternoon, more storms are expected in the surrounding
mountains will be capable of producing gusty, outflow winds in the
valley, even if the storms themselves do not enter the valley.
For the rest of southern Nevada, northwest Arizona and southeast
California...Winds should remain light and follow typical diurnal
trends for the next day or two outside of any thunderstorm outflow.
The Sierra Nevada will continue to support afternoon thunderstorms
with coverage elsewhere, especially in southeast California and
northwest Arizona increasing both this evening and again Wednesday
evening. Gusty and erratic outflow winds around 40 MPH look like for
the Colorado River Valley.
&&
.SPOTTER INFORMATION STATEMENT...Strong wind gusts are likely
today from thunderstorm activity across Northwest Arizona and
along the Colorado River Valley. Spotters are encouraged to report
any significant weather, such as heavy rainfall, strong wind
impacts, or blowing dust according to standard operating
procedures.
&&
DISCUSSION...Pierce
AVIATION...Steele
For more forecast information...see us on our webpage:
https://weather.gov/lasvegas or follow us on Facebook and TwitterThe Las Vegas radar (KESX), 149 km away, was scanning. The volume nearest the first event began at 00:58 UTC.
1 flash flood, 1 thunderstorm wind. Local standard time, as filed.
Huffriter Crossing and Pump Station Road were closed due to flooding.
Thunderstorm winds blew down power lines in Oatman.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2020Every state in 2020This day in weather historyWarnings in Arizona, August 2020
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 911551, 911554.