Las Vegas Sun

March 28, 2024

Warnings flow as flood season nears

Sometimes, however, there is virtually no warning. Threatening thunderstorms rush into the valley before homeowners can whisk in lawn furniture or close their car windows.

Next week the summer thunderstorm season -- and flash flood season -- begins in the Las Vegas Valley.

Today, the Clark County cities of Las Vegas, Henderson, North Las Vegas, Boulder City and Mesquite are being presented with the National Oceanic and Atmospheric Administration National Weather Service's StormReady designation.

The cities met rigorous certification requirements established by the StormReady Advisory Board for disaster preparedness and severe weather educational activities, officials said.

But the Las Vegas Valley can never be too ready, Clark County Regional Flood Control Manager Gale Fraser said.

Since the Nevada Legislature created the flood control district in 1985, the district has spent $836 million to build flood controls such as basins and channels. There are now 59 detention basins and about 337 miles of channels and storm drains throughout the county.

"While we've made significant progress with flood control improvements, there is still a lot more to be constructed," Fraser said. "Longtime residents will notice fewer and fewer areas are flooding during major storms. But until we are finished building all that is needed to protect Southern Nevada from floodwaters, residents still need to take precautions."

Rosie Ward, a local resident since 1968, vividly recalls a July 1975 flood that stacked more than 300 vehicles like cordwood in the parking lot of Caesars Palace.

"I couldn't believe all those cars stacked on top of one another," Ward said.

Another veteran flood-watcher said summer rains couldn't come soon enough for him.

"I kind of hope it rains; it's been so damn dry," said Vern Bostick, retired from the Clark County Soil Conservation Service.

As temperatures soar above 100 degrees every day under blue, cloudless skies, devastating flash floods hardly cast a shadow in the minds of most residents and visitors.

Many forecasters are predicting that this summer's rainfall total will be less than normal. But even in times of drought, summer storms can pose flood dangers, especially to people who don't realize that the Las Vegas Valley is susceptible to flash flooding in the summer.

Because roughly 6,000 people move into the valley each month, "it's so important to continue to get the message out about flood safety," Regional Flood Control District Public Information Officer Betty Hollister said.

"While we haven't seen much rain in the past few years, that doesn't mean we won't have major storms this summer. When the next storm hits, residents need to use good judgment and not take unnecessary risks by driving through flooded areas."

Clark County weather records indicate there have been 184 floods here since 1905.

The records show that while flash flooding can occur in any month, the most intense floods occur from July through Sept. 30.

Since 1960 the area has had at least nine floods that each caused at least $1 million or more in damage. Those floods also killed nine people.

Why do such devastating floods race across the Las Vegas Valley?

During the hot summer months, moist, unstable air from the Gulf of Mexico is forced upward by hot air currents, said Timothy Sutko, senior hydrologist for the Clark County Regional Flood Control District.

The thunderstorms that occur from this air flow, called Southwest monsoons, often result in spectacular lightning displays and downpours in parts of the valley.

As intense rain falls on steep mountain slopes and hardened desert or paved urban surfaces, the rainwater runs rapidly downhill from the western edge of the valley into the lower eastern sections.

The most recent devastating flash flooding occurred on July 8, 1999, when torrential rains hit the entire Las Vegas area.

Two people died as a result of the flooding. One person drowned in the Flamingo Wash; the second death was a result of a weather-related accident.

Damages to public property alone reached an estimated $20.5 million, and the Clark County Commission declared a state of emergency on July 9, 1999.

The governor issued a declaration of emergency and requested assistance from the Federal Emergency Management Agency on July 15, and President Clinton declared the area a federal disaster area on July 19.

One of the most riveting features of that storm was the size of the area where intense rain fell, Sutko said.

Simultaneously, rain fell over the northwest, west and southwest parts of the valley, resulting in heavy flows in the Flamingo Wash, Duck Creek and the Las Vegas Wash.

Within the Las Vegas Valley, two rain gauges maintained by the flood control district recorded over 3 inches of rainfall, five others reported over 2 inches of rain and another dozen captured 1.5 inches. Most of the rain fell in less than two hours.

As floodwaters swirled across the valley, the flows united above Lake Las Vegas where an early peak flow is estimated to have reached 16,000 cubic feet per- second, a rate never recorded in the valley before or since.

Important indications of this approaching storm appeared days before the weather struck, Sutko said.

Two days before the storm, dewpoint temperatures increased rapidly, from values in the mid-30-degree range to as high as the 50s and mid 60s. The increase was due to extremely moist air moving into the area.

What was most unusual about this particular storm, Sutko said, was that the intense rains fell in late morning, without afternoon heating and the resulting lift, the more common trigger for summer thunderstorms.

The National Weather Service issued its first weather advisory at 3:45 a.m. that day, based on heavy rainfall in northern Clark County and southern Lincoln County, north of Las Vegas. The advisory included a flash flood watch for Las Vegas.

The rain began falling in the valley before 9:30 a.m., intensifying so that by 10 a.m. nearly one inch was recorded in the Lone Mountain area.

Meanwhile, an intense band of rain cells developed south of the county, moving into the valley and merging with the original storm. The larger storm rained on the valley until shortly after noon.

McCarran International Airport operated under a "weather hold," from 11 a.m. until noon, keeping 20 departing flights on the ground and diverting four flights to Los Angeles.

Five mobile homes were destroyed in the Miracle Mile Mobile Home Park along Flamingo Wash at Boulder Highway.

Officials are hoping that the work that has been done since then will mean that destruction was the last of its type. But they're watching the skies and waiting to see how the valley holds up against Mother Nature.

archive