Las Vegas Got More Than a Third of its Annual Rainfall in Just Four Days

It’s only the first week of the month and Las Vegas has already recorded its wettest May on record after a storm system delivered rain to the city for four days straight. In the Las Vegas suburb of Henderson, a man was swept away by floodwaters on Tuesday.

The rains, considered rare for this time of year, came after a big low-pressure system dropped from the north down into the Mojave Desert, which includes southeastern California, southwestern Nevada and small portions of Arizona and Utah. The system hunkered down over the region and intermingled with moisture flowing in from the Pacific Ocean.

“It was kind of unusually placed over the Mojave Desert, and it was very slow to move out,” said Chris Outler, a meteorologist with the National Weather Service in Las Vegas. “It’s very unusual.”

May is typically the second-driest month in the Mojave, which usually gets most of its rainfall during the summer monsoons and winter months. But from Saturday through Monday it saw persistent rain, and on Tuesday thunderstorms delivered heavy downpours, strong winds and hail up to the size of quarters. On Tuesday, the Weather Service issued multiple warnings for severe thunderstorms across the eastern Mojave Desert, from east San Bernardino County in California into the Las Vegas area and all the way east into Bullhead City, Ariz.

In records dating to 1937, a Weather Service rain gauge at Harry Reid International Airport in Las Vegas recorded four days of consecutive rain, something it had never done before in May. By Tuesday, it had recorded 1.44 inches, marking the wettest May ever and beating a previous record of 0.96 inches set in 1969.

To put this in perspective, in a typical year, Las Vegas receives about 4.18 inches of rain. It received more than a third of that in just four days.

These totals may seem insignificant compared with the higher amounts of rain that have recently fallen in other parts of the country. A gauge in Kentucky picked up more than 15 inches of rain during flooding downpours in the Central United States in early April. But it’s a lot in the middle of an arid landscape at a time of year when rain is usually scarce. In a typical May, Las Vegas records 0.07 inches of rain.

Amid the downpours, water flooded streets in the Las Vegas area, and on the Strip a river flowed through the parking garage at the Linq hotel and casino. The garage often floods as part of a natural drainage system that controls water flow around the Strip.

In Henderson on Tuesday, a man was swept away by water pouring into a wash, an area that water flows into during heavy rains.

Lindsay Vukanovich, a spokeswoman for the Henderson Police Department, said firefighters and police officers arrived at the scene a little after 2 p.m. A firefighter briefly saw the man before “he was quickly immersed back underwater.”

As of Wednesday morning, the man had not been found, Ms. Vukanovich said. She also said the police department had not been able to identify him.

It is not possible to draw a connection between a particular rain event and climate change in real time. But a large body of research indicates that climate change is resulting in more extreme weather events. Nevada is the driest state in the nation and marked by episodes of long dry periods and periodic, often intense storms. Scientists say climate change is intensifying these conditions.

Just across the Nevada border in Mohave County, Ariz., thunderstorms generating strong winds kicked up a dust storm, known as a haboob, the Weather Service reported.

“There’s a big dry lake bed over there and when thunderstorms pass through, they can pick up dust,” said Mr. Outler, the meteorologist.

The storm was pushing out of the region on Wednesday, with just a few lingering showers expected in Mojave County, Ariz.

Dry weather and warmer weather is forecast in coming days with highs in the 90s over the weekend.

“No more rain in Las Vegas today,” Mr. Outler said.