Monsoon season raises flash-flood concerns in Las Vegas Valley

Southern Nevada’s 2018 monsoon season may to be wetter than normal, prompting warnings for residents to be ready for potentially deadly flash flooding.

A new long-term forecast this week said there is up to a 40 percent chance that the seasonal rain and thunderstorms in the Southwest will be heavier than normal this year

The Southwest monsoon season typically runs from early July to mid-September, but it varies depending on weather conditions.

Southern Nevada might see some moisture as soon as the Fourth of July, said National Weather Service meteorologist John Adair, who works in the weather service’s Las Vegas office.

“We’re seeing the possibility of moisture starting to approach northwest Arizona, Southern Nevada as we get into Tuesday, Wednesday next week, which is about normal for Southern Nevada,” he said.

Other than the chance that rainfall could be above average, it is too early to say much more about the upcoming monsoon season, Adair said.

The thunderstorms are not expected to do much to alleviate the extreme drought conditions gripping a large swath of the Southwest, he said. Southern Nevada is experiencing a moderate drought.

Winter storms tend to bring more widespread precipitation that do more to ease droughts, he said.

“In the monsoon season we get thunderstorms that kind of pop around,” Adair said. “It can help a little bit, especially if we get lots of thunderstorm days, but we really rely on the fall, winter, early spring precipitation.”

But summer thunderstorms, which can be intense in localized areas, frequently trigger flash flood warnings, which are issued when the life-threatening torrents are imminent or already happening, Adair said.

“People just need to be aware of their surroundings” and seek higher ground when flash floods are possible, he said.

The Clark County Regional Flood Control District is in the middle of a project to install drainage tunnels in the northwest valley that should help.

The addition to the flood control network, which will cost more than $20 million, is expected to be completed by December. It is one of 19 flood district projects under construction, about to start construction or out for bidding, totaling nearly $115 million. The district is made up of representatives from the county and each incorporated city in the county.

Authorities warned at a news conference Wednesday that residents should avoid the developed flood channels when thunderstorms appear.

The flood tunnels are particularly dangerous for Las Vegas’ homeless, who often camp in the washes.

Keeping an eye on weather forecasts also is advisable, as Adair said thunderstorms can usually be predicted one to three days in advance.

“As far as pinpointing when thunderstorms develop, that’s a day-by-day process as the moisture increases over Southern Nevada,” he said. “Most of the time we just kind of look to see how much moisture is available.”

Contact Katelyn Newberg at knewberg@reviewjournal.com or 702-383-0240. Follow @k_newberg on Twitter. Review-Journal staff writer Blake Apgar contributed to this report.

A previous version of this article incorrectly stated that the Southwest was forecast to receive 33 percent to 40 percent more rain than average.