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September 4, 2015

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As rain enters forecast, monsoon season descends on Las Vegas Valley

Image

Sam Morris

A bike rider tries to cross a flooded intersection near Sahara Avenue and Mojave Street after rainstorms hit the Las Vegas Valley on Tuesday, Sept. 11, 2012.

Rain, Flash Flooding, Rescues and Cleanup

A Knudson Middle School student hangs onto a tree after falling down and being dragged by  floodwater near Eastern and Sahara avenues, Sept. 11, 2012. Launch slideshow »

Flooding in Henderson: Aug. 22, 2012

A Henderson police officer blocks the eastbound roadway of Sunridge Heights Parkway between Seven Hills Drive and Coronado Center in Henderson Wednesday, August 22, 2012. Launch slideshow »

Flash Floods

Pedestrians wade across Craig Road near U.S. 95  after a powerful thunderstorm dumped three inches of rain in about 90 minutes in the northwest section of the city Wednesday, August 19, 2003. The torrential downpour caused flash flooding that swamped neighborhoods and trapped people in their cars. Launch slideshow »

The flash floods and heavy rains seen briefly Sunday on the east side of the Las Vegas Valley were merely a preview of what's to come.

Yes, Southern Nevada's monsoon season is imminent. With the season, heavy rainfall, thunderstorms, hail, flash floods, windstorms and more extreme weather conditions usually arrive. And with Las Vegas right in the path of a large amount of atmospheric moisture moving off the west coast of Mexico, residents throughout the valley could see monsoon conditions as soon as Wednesday, the National Weather Service says.

Southern Nevada’s monsoon season usually lasts from July to October. It is caused by tropical storms or hurricanes pushing huge amounts of moisture up through the Gulf of California. The moisture is channeled through mountain ranges into the American Southwest, where it is converted into the type of huge thunderclouds seen Sunday throughout Henderson and east Las Vegas.

A tropical storm moving Monday off the coast of Mexico could lead to monsoon conditions as early as Wednesday, said Ryan Metzger, a National Weather Service meteorologist. At such an early state, it's difficult to tell how severe the storm will be, but Metzger said this type of weather behavior was typical for early July.

One of Metzger's main concerns with monsoon-driven storms is the strong potential for flash floods. Because Las Vegas is in a valley, and with much of the ground covered by asphalt, excess water can quickly overwhelm and flood low-lying areas, Metzger said.

Flash flooding can prove deadly. At least two deaths in the 2012 monsoon season were related to drowning in flood-control channels. In August, Green Valley High School student William Mootz, 17, drowned in a flood-control channel, where floodwaters were racing at more than 5,000 cubic feet per second, after putting his foot in the water and being swept away.

Another man drowned after attempting to move a piece of equipment from a flood-control area during a monsoon rainstorm.

Both incidents are evidence to stay away from the channels during the monsoon season, Metzger said.

"When it's raining out, the flood-control channels fill very quickly and the water is moving very quickly," Metzger said. "It's definitely a place to avoid."

Driving can also be difficult during monsoon storms, he said.

"Roads have a lot of oil and rubber built up, so when the water hits, it becomes pretty slippery," he said. "It's definitely a hazard until that gets washed off."

Metzger said other concerns with monsoon season include hail, windstorms and lightning strikes. A windstorm last week in North Las Vegas destroyed around 15 trees and damaged several cars, and authorities blame the current wildfire raging through Mount Charleston on a lightning strike.

Monsoons do have a benefit — the season provides a significant portion of the region's yearly rainfall, Metzger said.

"We get a big chunk of our average rainfall during the monsoon season, which is definitely important to the climate," he said.

On average, Las Vegas receives around an inch of rain during monsoon season, but the number can easily fluctuate — in 1984, the National Weather Service recorded 4.16 inches of rain at one location over the course of the monsoon season.

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