Moisture-laden air spreading across the Southwest in recent days has brought much-needed rain to drought-ridden areas, while also unleashing thunderstorms, dust storms, strong winds and flooding. This seasonal weather pattern, known as the monsoon, has led to some spectacular — albeit disruptive and even dangerous — weather.
In the Nevada desert, winds toppled tents and briefly shut down the entry gates to the Burning Man festival this weekend. In Phoenix on Monday, a wall of dust moved through the city and grounded flights at the airport. By Wednesday, waterfalls at Yosemite National Park that are typically dry at this time of year had started flowing.
The monsoon affects the West every summer, though its duration and strength vary annually. It occurs when the prevailing winds shift from the west to the south, transporting moisture into the Southwest from the Sierra Madre ranges in Mexico, the Gulf of Mexico and the Pacific Ocean.
Its effects are usually strongest in Arizona and New Mexico, where heavy thunderstorms can bring cooler weather on hot days, but the moisture can spread across the region, as far north as Colorado and Northern California.
The onset of the monsoon varies every year, but it generally begins affect the Southwest in July and runs into September. This season it came late — “about as late as it can get,” said Mike Kaplan, professor emeritus at the Desert Research Institute in Reno, Nev.
The delay meant that Arizona and New Mexico had been unusually dry so far this year. The Dragon Bravo fire exploded in Grand Canyon National Park in July, in part, because the landscape was more parched and vegetation more flammable from a lack of monsoon rains.
“As some of my friends in the business say, it was a non-soon,” Mr. Kaplan said.
But starting last weekend, the weather pattern changed, and moisture streamed into the Southwest. Storms pounded mountains and valleys across the region. Rain has fallen over the area affected by the Dragon Bravo fire and across the Southwest.
“Pretty much everywhere from Arizona and Mexico to Idaho and Wyoming, and not including the California Coast, has seen some rain,” said Frank Pereira, a meteorologist with the Weather Prediction Center.
Some of the most intense storm activity has been in Arizona, where on Monday afternoon, a dust storm formed in the southern part of the state as winds surged down from thunderstorms. The ominous cloud of dust kicked up by the winds traveled along Interstate 10 to Phoenix, engulfing the city and briefly grounding flights at Phoenix Sky Harbor International Airport.
“In the seven years that I’ve been here, it was the biggest that I’ve seen,” said Sean Benedict, a meteorologist with the Weather Service in Tempe. “It was very large in terms of height and how far it stretched.” He said forecasters estimated the dust cloud was 6,000 to 8,000 feet tall, or about as tall as five Empire State Buildings.
Dramatic scenes have unfolded in Nevada in the Black Rock Desert, where the Burning Man festival is taking place. Wind gusts reached 45 miles per hour on Saturday, whipping up a dust storm and leaving four people with minor injuries, organizers said.
The storms can bring rain or dust, both hazardous conditions in the remote desert. On Tuesday, the Pershing County Sheriff’s Office said, a man who was not identified was airlifted out of the festival for medical attention after he reportedly suffered an electrical shock when he stepped into a puddle of water. His condition on Wednesday was unknown.
Light rainfall has also wetted the ground in recent days, leaving the Playa, the lake bed where the festival takes place, sticky. There was a chance for storms in the region again Wednesday.
In California, thunderstorms brought rain to Yosemite National Park that recharged the famed Yosemite Falls, which usually goes dry in late August.
“It was basically dry, maybe the tiniest of trickles, and these big rains brought it back to life,” said Cory Goehring, a senior naturalist with the Yosemite Conservancy.
Other waterfalls appeared. Alex Breitler, a hiker, said he was in Tuolumne Meadows in the park on Saturday afternoon when waterfalls flowed down the sides of Lembert Dome during a torrential downpour. Mr. Breitler had planned to climb the granite monolith but scrapped those plans because of the stormy weather.
“The waterfalls were gone in five to 10 minutes, but it was really a pretty spectacular sight,” he said.
To the south in Palm Springs, Calif., wind gusts reached 54 miles per hour and the temperature plummeted from 102 degrees to 71 degrees in an hour on Monday afternoon, as thunderstorms released record-breaking rainfall that inundated city streets with nuisance flooding. A total of 0.44 of an inch was recorded at Palm Springs International Airport, surpassing the previous same-day record of 0.26 of an inch, said Sam Zuber, a meteorologist with the Weather Service.
The chance for isolated storms across the Southwest was expected to taper off by Thursday and Friday.
Mr. Pereira said Labor Day weekend was expected to be “mostly dry” west of the Rocky Mountains.
Amy Graff is a Times reporter covering weather, wildfires and earthquakes.
The post Southwest Monsoon Finally Arrives, With a Chaotic Mix of Dust and Rain appeared first on New York Times.
