Flash flooding always in valley’s summer forecast

Instead, Las Vegas Valley residents should be wary of the upcoming monsoon season, which starts later this month and usually brings flash flooding that can be destructive and deadly, officials said Monday at a flood season kickoff news conference.

“Flooding is an issue in the most arid part of the country,” said Las Vegas City Councilman Larry Brown, who also is chairman of the Clark County Regional Flood Control District. “Five (thousand) to 6,000 people move here each month, and they don’t know diddly about what (a) danger floods can be in the valley.”

Southern Nevada’s desert climate disguises the valley’s susceptibility to severe flash flooding in July, August and September, when the annual monsoon pushes moist air from the gulfs of Mexico and California into the valley, according to the National Weather Service.

The weather shift results in sudden thunderstorms. Although the monsoon months see less precipitation than January, February and March, storms are more intense during the monsoon.

The average monsoon season produces around one inch of rain — roughly a quarter of the annual amount — but it also has resulted in around two-thirds of the valley’s annual number of thunderstorms. And monsoon seasons have produced as much as around 4 inches of rain in the past, according to the weather service.

Rock-hard dry ground and uneven topography can turn downpours into rushing currents that move east toward Lake Mead. Even just a few inches of quick-moving water can sweep away people and cars.

“When it starts to rain, parents should know where their kids are, and keep them inside. It’s dangerous,” said U.S. Rep. Shelley Berkley, D-Nev. “Sprinkles are one thing. Flooding is another. Sprinkles can quickly turn to flooding.”

Likewise, drivers are urged to avoid driving through roads that are flooded, which could be damaged or covered with debris concealed by rising waters, according to the flood control district.

“If it is raining, try to restrict your driving. Don’t get on the roads,” Berkley said. “They’re going to be treacherous, no matter what.

“We don’t want to get you in a position where you cling to a tree and hope the helicopter squad will rescue you in time,” she said.

Las Vegas police conduct around 200 helicopter rescues each flood season, said Officer Jim Roberts with the department’s search and rescue team.

“Without a doubt, floodwater rescue operations are the most dangerous thing we do,” Roberts said.

As part of Monday’s media event, police did a rescue demonstration, plucking a volunteer from the roof of a truck “stranded” amid a bone-dry flood channel.

This year’s monsoon forecast is somewhat hazy. In the Southwest as a whole, modeling doesn’t indicate whether rainfall be greater or less in volume, according to the National Weather Service. But less rain is expected in Northern Nevada, something that may carry over to Southern Nevada.

“We’ve certainly been trending below-normal for the past several months. There’s a good chance that will end up continuing as well,” said Stan Czyzyk, a science operations officer with the weather service’s Las Vegas office. “Overall, it’s trending slightly below normal for precipitation.”

The wettest monsoon season on record, as measured by monitors at McCarran International Airport, was in 1984 when 3.94 inches of rain fell.

But in recent years there have been incidents of flooding that have had devastating consequences. In 2003, an afternoon deluge resulted in 60 rescues and sent floodwaters into dozens of homes in northwest Las Vegas. Some areas reported 3 inches of rain in a 45-minute period. Four years earlier, two people died and $20 million in damage resulted from a 90-minute July downpour that also dumped 3 inches of rain on some parts of the valley.

In hopes of minimizing flooding to streets and neighborhoods, officials recently completed the Tropicana-Flamingo Wash flood control network. The $336 million system encompasses eight flood basins and 27 miles of flood channels in the southwestern valley, according to Betty Hollister, a spokeswoman with the flood control district.

That brings the valley’s flood control network up to 75 basins and 450 miles of channels built at a cost of $1.2 billion over the past 20 years. Over the next 30 years, planners expect to build another 60 basins and 400 more miles of channels, Hollister said.

More information is available by calling the flood control district at 455-3139 or online at www.regionalflood.org.