From dry to deluge, how heavy snow, rain flooded Yellowstone

RED LODGE, Montana (AP) — Just three months in the past, the Yellowstone area like many of the West was dragging by way of an prolonged drought with little snow within the mountains and wildfire scars in Red Lodge from a yr in the past when the realm was hit by 105-degree Fahrenheit (40.5 Celsius) warmth and hearth.

Rivers and creeks this week raged with water a lot increased and sooner than even the uncommon benchmark 500 yr flood. Weather-whiplashed residents and authorities officers raced to avoid wasting properties, roads and companies.

Mostly pure fleeting forces with some connections to long-term local weather change mixed to set off the swap from drought to deluge, scientists mentioned.

It was a textbook case of “weather weirding,” mentioned Red Lodge resident and National Snow and Ice Data Center deputy lead scientist Twila Moon. Her cropped hair was up in a sweat band and he or she was lined head to toe in mud from serving to residents filter out flooded areas.

Patrick Sipp, co-owner of Flying Pig Adventures, pets his dog, Bonnie, as employees Jackson Muller, right, and Christie Davis sit in a raft while Yellowstone National Park is closed due to historic flooding in Gardiner, Mont., Wednesday, June 15, 2022. “We’re definitely a resilient company, we’ve got a very tough crew,” Sipp said. “But it’s devastating. You just hate seeing stuff like that in the community. We’re just hoping that we can get back out there relatively soon.” (AP Photo/David Goldman) MTDG102 MTDG102

But these had been circumstances distinctive to the northern inside West, scientists say. Most of the West doesn’t have a lot snow and can maintain scuffling with drought.

In the Yellowstone space, after a winter with mild snow, it lastly collected a few months in the past, moist and chilly, doubtless due to the pure climate occasion La Nina, constructing the snowpack within the mountains to above regular ranges. Snow fell so laborious on Memorial Day weekend individuals needed to abandon tenting gear and get out of the park whereas they might, mentioned Tom Osborne, a hydrologist who has spent a long time within the space.

Things seemed good. The drought wasn’t fairly busted — in truth Thursday’s nationwide drought monitor nonetheless places 84% of Montana below unusually dry or full-fledged drought circumstances — but it surely was higher. Then got here an excessive amount of of a moist factor. Heavy rains poured in due to a water-laden environment turbocharged by hotter than regular Pacific water. And when it poured, it melted. The equal of 9 inches (23 centimeters) of rain flowed down Montana mountain slopes in some locations. Half or extra was from the melting snow, scientists mentioned.

All the rivers and streams reacted the identical: “They shot up to levels far beyond anything ever recorded,” Osborne mentioned. “Hydrologists know that there’s nothing that causes higher magnitude flooding in the West more so than a rain-on-snow event.”

One gage on the Stillwater River close to Absarokee, the place Osborne lives, usually flows at 7,000 cubic toes (200 cubic meters) per second throughout a reasonable flood and races at 12,400 cubic toes (350 cubic meters) per second in a 100-year flood, he mentioned. A once-in-500-year flood would imply water raging at 14,400 cubic toes (410 cubic meters) per second. Preliminary numbers present that on Monday, it crested at 23,700 cubic toes (670 cubic meters) per second, the equal of stacking three reasonable floods on prime of one another, in line with Osborne.

La Nina circumstances happen when elements of the equatorial Pacific ocean cool, altering international climate patterns. While La Nina can dry out the U.S. Southwest, it will possibly enhance snow and rain in different extra northwesterly elements of the nation and should have helped pack extra snow in Yellowstone’s mountain peaks, in line with Upmanu Lall, the director of the Columbia Water Center at Columbia University.

And whereas Oregon, Washington, Idaho and Montana had greater snowpacks from a chilly, moist spring, areas south of that had been extraordinarily dry with anemic to lacking late spring snows, mentioned UCLA local weather scientist and western climate professional Daniel Swain.

Then an “atmospheric river” — lengthy flowing areas within the sky that transfer giant quantities of water — entered the realm and dumped rain on the snow at a time when the climate was heat. That rain got here in from over the northern Pacific the place the water and air was unusually heat and hotter air holds extra rain attributable to primary physics, mentioned Swain. That’s a small local weather change connection, he mentioned.

Over the long-term, local weather change is lowering snowpack within the West, in line with Guillaume Mauger, a analysis scientist on the University of Washington Climate Impacts Group.

“With climate change, we expect less snow and we expect the melt season to be shorter,” mentioned Mauger.

But the spring didn’t observe that long-term sample.

“What is extraordinary is the combination of that high snowpack that got built up in April, May, together with this rainfall event and the warmer conditions,” Lall mentioned. “That’s where the flooding is coming from.”

Lall mentioned an atmospheric river that introduced in moisture from the Pacific “is a little bit harder” to hyperlink to local weather change.

La Nina could have performed a task in a number of methods. While there have been La Ninas like this one all through the previous “we’ve never seen in human history persistent La Nina events with global temperatures this warm before. That is a unique combination,” Swain mentioned. “We already know that La Nina increases the risk of floods in some places. It increases the amount of active weather in some places. And then you have warmer oceans and a warmer atmosphere that can supercharge those.”

“So you really can’t just say it’s one thing or the other,” Swain mentioned. “It really is both. It’s the natural and the unnatural together.”

A yr in the past, Montana local weather scientists created the Greater Yellowstone Climate Assessment and it warned of rain-and-snow occasions like this, mentioned report co-lead creator Cathy Whitlock, an Earth sciences professor at Montana State University.

But the true life flooding catastrophe was far worse, she mentioned.

“Who could predict houses going into the rivers and bridges being destroyed,” Whitlock mentioned. “It’s so much worse than you imagine. And it’s partly because the infrastructure is not set up for extreme climate events.”


Borenstein reported from Kensington, Maryland; Phillis from St. Louis.


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