Southeasterly flow pulled monsoon moisture up into the eastern Mojave Desert, fueling scattered thunderstorms over Mohave County. Some storms produced flash flooding.
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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.
Southeasterly flow pulled monsoon moisture up into the eastern Mojave Desert, fueling scattered thunderstorms over Mohave County. Some storms produced flash flooding.
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 21, 2:25 PM MST, 3 hours 15 minutes earlier.
Area Forecast Discussion National Weather Service Las Vegas NV 225 PM PDT Tue Aug 21 2018 .SYNOPSIS...Expect decreasing winds overnight with afternoon breezes on Wednesday. Monsoon moisture will remain in place through Thursday over Mohave County where the best chance for thunderstorms will continue. Dry conditions with seasonal temperatures on Friday and over the weekend. && .NEAR TERM...through the afternoon. Visible satellite imagery shows an obvious counter clockwise spin near Nogales AZ moving north. SPC mesoanalysis shows moisture axis extending from the lower Colorado River Valley up through Mohave County where 850mb moisture transport vectors indicate the best potential for storms producing heavy rain. RAP has moderate to strong instability focused across Mohave County with the area of highest CAPE and lowest LIs lifting north through the afternoon. Otherwise, there is nothing obvious in current observational data that would indicate other areas that would be favorable for near term development. 130 pm wind gusts across the region are in the 25- 35 mph range which remains under advisory levels. Temperatures overall are running 3-6 degrees cooler than yesterday, in line with the forecast. Tonight through Friday... Once daytime heating is lost at sunset, storm development should dissolve with no other driver in place to maintain convection into the overnight hours. The moisture/instability gradient remains over essentially the same area (from the Mojave Preserve to Las Vegas to Mesquite) Wednesday and Thursday however, the region of deeper moisture and better instability is further east. Thunderstorm chances linger over primarily Mohave County Wednesday and Thursday afternoon before mainly dry conditions return for Friday. Temperatures will be near to slightly above normal through Friday. LONG TERM....Saturday through Tuesday. Little change in the long term forecast as southwest flow will bring in drier air across much of the region and keep monsoonal moisture confined to northwest AZ through the weekend. By Sunday, the medium range models bring in a trough across the NW states which will result in increased southwest winds. By Monday, models are in pretty good agreement and dig this trough further into the Great Basin region through Tuesday. This trough will likely scour out the remaining low grade moisture over northwest AZ and bring gusty to windy southwest winds across the region. As of now, these winds look to be below wind advisory criteria. Otherwise, expect mostly clear skies and near or slightly above normal temperatures through the period. && .AVIATION...For McCarran...Breezy southeast winds are expected to continue through the rest of the day, eventually subsiding overnight tonight. Peak winds gusts of 30-35 kts are possible between the 21- 04Z time frame before beginning to subside and the potential for gusts up to 25 kts may linger as late as 08Z tonight. Models continue to produce storms this afternoon but latest runs keep most activity east of the KLAS terminal. So left VCTS out of the TAF with this package as confidence is still low for terminal impacts. However, this is not to say that an isolated cell is out of the question this evening. If so, erratic outflow winds will be the main impact. For the rest of southern Nevada, northwest Arizona and southeast California...Gusty southerly winds will begin to overspread the region through the rest of the morning and into the afternoon. Strongest southwest winds are expected between 20-02Z later this afternoon and evening with gusts to 25-35 kts. Thereafter, winds should steadily decrease with gusts dropping off by 06-07Z tonight and then should return to diurnal winds by the early morning. Models develop isolated to scattered storms late this evening as far west as the I-15 corridor and best chances for VCTS should be for KEED and KIFP. && .FIRE WEATHER...Isolated to scattered thunderstorms over Mohave County Wednesday and Thursday otherwise southwest winds with gusts to around 25 mph on Wednesday. Relative humidity under 20 percent across much of the region on Wednesday except in eastern San Bernardino, southern Clark and Mohave counties. Drier conditions push into all areas expect Mohave County on Thursday. Mainly dry conditions area wide Friday and over the weekend. && .SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report any significant weather or impacts according to standard operating procedures. && SHORT TERM...Salmen AVIATION...Boucher LONG TERM...Kryston For more forecast information...see us on our webpage: http://weather.gov/lasvegas or follow us on Facebook and Twitter
The Cedar City radar (KICX), 71 km away, was scanning. The volume nearest the first event began at 00:39 UTC.
7 flash flood. Local standard time, as filed.
Rosy Canyon Road was closed from Cane Beds to the Utah state line.
All major roads in Colorado City were flooded. A nearby rain gauge measured 3.70 inches between 1130 PM on the 21st and 617 AM on the 22nd.
Huffritter Crossing was closed from Highway 93 to Back Road.
Bogie's Ranch Road was closed.
Pump Station Road was closed.
Banegas Road was closed.
Signal Road was closed from Highway 93 to Alamo Road.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2018Every state in 2018This day in weather historyWarnings in Arizona, August 2018
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: 779324, 779325, 779327, 779335, 779338, 779342, 779348.