Las Vegas floods June 2016

Intense thunderstorms pounded the Las Vegas area on Thursday with golf ball-sized hail, gusty winds, destructive lightning and sheets of rain that swamped busy intersections and left at least one person hospitalized after she was plucked from a flooded wash, authorities said.

The woman was believed to have suffered a heart attack while she and two other people were rescued from rushing water near the Hard Rock Casino Hotel east of the Las Vegas Strip, Deputy Clark County Fire Chief Jeff Buchanan said.

Firefighters reached two other people and their dogs in another wash near Boulder Highway, about 5 miles east of the Strip, and rescued another two people at another site shortly after 6 p.m., Buchanan said.

At least 21 airline flights were diverted from busy McCarran International Airport, where the National Weather Service said wind gusts were clocked at 56 mph during the height of the storm.

Several vehicles stalled with water up to their headlights in one flooded intersection in nearby Henderson.

"People don't realize just a few inches of rain can really cause some damage," said Kim Becker, a Henderson city spokeswoman.

Monsoon-style summer storms aren't unusual in the desert around Las Vegas, where one or two storms can go a long way toward filling rain gauges that average only 4.19 inches of rainfall a year.

But heavy rain can turn to torrents sluicing off sun-baked desert or pavement into miles of flood channels constructed to protect homes and businesses.

Weather service meteorologist John Adair said Henderson received up to 1 1/2 inch of rain between 2 p.m. and 3 p.m. Red Rock Canyon, about 25 miles west of the Strip, received more than 1 1/4 inches, and Adair said flooding closed the scenic 13-mile loop road through the preserve.

Adair called the 2-inch hail that fell in southwestern neighborhoods near the 215 Beltway the most unusual element of the storm. Hail the size of 25-cent pieces pelted Henderson.

Winds felled at least one tree, and Buchanan said lightning sparked a house fire that displaced two adults and their pet dogs.

NV Energy reported almost 4,700 customers without electricity shortly after the rain stopped.

Traffic officials reported more than one lane of the U.S. 95 freeway closed for a time due to flooding not far from the Galleria at Sunset mall in Henderson.

Airport spokeswoman Christine Crews said flights that were waved off were sent to airports in California and Arizona. Some McCarran departures were delayed for more than two hours, she said.

Flood channels did their job, said Erin Neff, spokeswoman for the Clark County Regional Flood Control District.

Water gushed through some 600 miles of channels, including choke points near the Linq observation wheel on the Strip. The water level topped 22 feet at one key detention basin on the way toward the Colorado River and Lake Mead by about 4 p.m.

Neff said water flows were clocked at about 30 mph. She characterized the rain in some parts of the area as "unprecedented."

There's a slight chance of thunderstorms early Friday morning and a 50 percent chance of thunderstorms during the day, with a high temperature of 100 degrees expected.

On Saturday, it's expected to be partly sunny with a 20 percent chance of thunderstorms in the afternoon and evening. High temperatures are forecast to be 94-98 on the west side of the valley and 98-102 on the east on Saturday.

The storms will be gone by Sunday. For Independence Day on Monday, forecasters expect clear skies with a high of 107.

The Associated Press contributed to this report.