It's a fine line as the summer rainy season brings relief, and flooding, to the southwestern US

It's as if the sky opened up and dropped everything it had in a matter of minutes. Giant raindrops combined with hail to transform an otherwise toasty summer day into a white wintry scene, at least for a few minutes.

Then it all turned to red mud.

That's how the monsoon rolls in the southwestern United States, with thunderstorms and rain clouds hopscotching around as they bring much-needed moisture to a region where every drop counts. It's the time of year when Arizona and New Mexico receive about half of their annual precipitation, from mid-June through September. Northern Mexico logs even more.

From church altars and farm houses to city halls, prayers, songs and even festivals are held in hopes of having a bountiful monsoon, enough to water crops and provide drinking water but not too much to turn roads into rivers and wash away homes where wildfires have reduced mountainsides to ash.

It can be a fine line.

Here are some things to know about the North American monsoon:

Seasonal shift

The recipe relies on the buildup of summer heat and shifting wind direction, which helps funnel moisture from the Pacific Ocean, the Gulf of California and sometimes the Gulf of Mexico to areas where it's typically not found.

This means more showers and thunderstorms for the arid Southwest. Lightning, dust storms and strong winds also can be part of the mix.

The monsoon has ramped up a bit early this year, said Todd Shoemake, lead meteorologist with the National Weather Service in Albuquerque, New Mexico.

“A lot of the moisture that has been in place has been very high, very abnormally high,” he said. “And so that’s led to a lot of very intense thunderstorms with very heavy rainfall.”

Monsoons in other parts of the world often mean months of never-ending rain. Not so in northern Mexico and the American Southwest, where mornings often start with blue skies. Cumulus clouds begin billowing in the afternoon and within hours they let loose.

A monsoon features “bursts” and “breaks” depending on how much moisture is circulating and which way the wind blows.

Blessing and curse

This year's monsoon stranded travelers in a remote part of central New Mexico, leaving them in a thick soup of mud with little warning as a curtain of rain and lime-sized hail was unleashed.

In Moab, Utah, about a month's worth of rain fell in just 10 minutes. Water overflowed banks, bridges and sandstone cliffs. Homes were flooded and patrons at one tavern had to evacuate.

Heavy rain washed away important arteries linking communities in the Navajo Nation and first responders in New Mexico's largest city had a crush of calls for service as Albuquerque took on nearly 1.5 inches (3.8 centimeters) of water in less than 90 minutes, making many roads impassable.

In fire-ravaged parts of New Mexico, summer rains have become another threat. A black river of ash, soil and debris rushed down Ruidoso's main street, taking vehicles with it while homes and businesses flooded. It was the same in northern New Mexico, where numerous communities have yet to recover from the burn scars of a 2022 wildfire that was the largest in the state's recorded history.

But the monsoon also can be liquid gold for farmers and city water managers who are hopeful reservoirs can at least partially be replenished and river flows boosted. They are looking for any hedge against prolonged drought in a region that has seen increasingly erratic winter snowpacks and dwindling water supplies.

Ebb and flow

The 2021 monsoon was wet and the 2022 season got an early start. Right on cue, lots of moisture came in from the south and widespread rainfall was reported around the Southwest. That year ended as another above-average season.

But the following year was a dud, with some spots seeing only minimal precipitation. Many areas were grappling with severe and even extreme drought through the summer months.

This season might be packing quite the punch so far, but Shoemake said the monsoon appears to be growing more fickle.

“It has been a very mercurial monsoon pattern over the last five years,” he said. “Ups and downs, ebbs and flows.”

Forecasters are seeing more extreme events with climate change, he said, and the indicators they use to make long-term predictions are giving mixed signals.

“They aren’t telling us the story that we used to see, you know, 10, 20, 30 years ago. So it’s becoming a little bit more difficult to assess seasonal precipitation,” Shoemake said.

Officials with the Arizona State Climate Office noted the wide swing in the amount of moisture seen by some communities during the start of the monsoon, anywhere from 200% to 800% of normal precipitation amounts.

“Not unusual for how things go for an Arizona monsoon,” the office said.

A clean slate

The North American monsoon can have considerable variability. But one thing is certain: The season evokes a special kind of anticipation among those who consider the Southwest home.

Every tease of the monsoon — the smell of rain, the darkening of the sky and the rumble of thunder in the distance — carries memories of rainy summer seasons past.

At Monument Valley on the border of Utah and Arizona, Shaye Holiday's family spends hundreds of dollars each summer fixing roads leading to their homes at the edge of the Navajo monument and within the park's picturesque valley. Their tour business also takes a hit when the road through the park is shut down due to flooding and erosion.

But for his father's orchard and his grandmother's garden, the rain is a blessing. And for him, going home during the rainy season offers a chance to recharge. He loves seeing the puddles dotting the desert landscape as he drives the route north from Kayenta, Arizona.

“It’s just been uplifting and really pleasant to be back in Monument Valley, where Mother Nature is kind of wiping the slate clean," he said. “In a way, it's very refreshing.”