RED LODGE, Montana (AP) – Just three months ago, the Yellowstone region, like much of the West, was going through a prolonged drought with little snow in the mountains and signs of forest fires at Red Lodge a year ago when the area was affected by 105 degrees Fahrenheit (40.5 degrees Celsius) heat and fire.
Rivers and streams raged this week with water much higher and faster than even the rare 500-year flood. Residents and government officials raced to save homes, roads and businesses.
Mostly natural fleeting forces with some links to long-term climate change combined to trigger the shift from land to flood, scientists said.
It was a textbook about “strange weather”, said Red Lodge resident and deputy lead scientist at the National Snow and Ice Data Center Tuila Moon. Her cut hair was covered in sweat and she was covered from head to toe in mud to help residents clear the flooded areas.
But these were unique conditions for the northern interior of the West, scientists say. Most of the West does not have much snow and will continue to struggle with the drought.
In the Yellowstone area, after a winter with light snow, it finally accumulated a few months ago, wet and cold, probably due to the natural weather event La Nina, which raised the snow cover in the mountains above normal levels. The snow fell so hard on Remembrance Day weekend, people had to abandon camping gear and get out of the park while they could, said Tom Osborne, a hydrologist who has spent decades in the area.
Things looked good. The drought was not completely overcome – in fact, national drought monitoring on Thursday still puts 84% of Montana in unusually dry or full-blown drought conditions – but it was better. Then came something too wet. Heavy rains poured in thanks to a water-laden atmosphere, turbocharged by warmer than normal Pacific water. And when it was poured out, it melted. The equivalent of nine inches (23 centimeters) of rain flows down the slopes of Montana in some places. Half or more of the snow is melting, scientists said.
All rivers and streams reacted in the same way: “They have risen to levels far beyond anything ever recorded,” Osborne said. “Hydrologists know that there is nothing to cause larger-scale floods in the West more than rain on snow.”
A sign of the Stillwater River near Absaroki, where Osborne lives, typically runs at 7,000 cubic feet (200 cubic meters) per second during a moderate flood and competes at 12,400 cubic feet (350 cubic meters) per second at 100- annual flood, he said. One flood every 500 years would mean water rushing at 14,400 cubic feet (410 cubic meters) per second. Preliminary figures show it reached 23,700 cubic feet (670 cubic meters) per second on Monday, equivalent to three moderate floods piling up on top of each other, Osborne said.
“Many of these roads have been around for decades and have not seen any flood damage like what we saw,” said Lance Vanden Bugart, a meteorologist with the National Weather Service.
The storm hit the eastern end of the Custer Galatin Mountain National Forest, pouring five inches of rain in some places.
La Nina’s conditions arise when parts of the equatorial Pacific Ocean cool as global weather patterns change. While La Nina may dry up the southwestern United States, it may increase snow and rain in other more northwestern parts of the country and may have helped build up more snow in the Yellowstone mountain peaks, according to Upmanu Lall, director of Columbia Water. Center at Columbia University.
And while Oregon, Washington, Idaho and Montana had greater snow cover than a cold, wet spring, areas south of it were extremely dry with anemic to no late spring snow, said UCLA climatologist and Western weather expert Daniel Swain.
Then an “atmospheric river” – long flowing areas in the sky that carry large amounts of water – entered the area and poured rain on the snow at a time when the weather was warm. The rain came from the North Pacific, where the water and air were unusually warm and the warmer air held back more rain due to basic physics, Swain said. That has little to do with climate change, he said.
In the long run, climate change is reducing snow cover in the West, according to Guillaume Mogher, a researcher at the University of Washington’s Climate Impact Group.
“With climate change, we expect less snow and we expect the melting season to be shorter,” Mauger said.
But spring did not follow this long-term pattern.
“What’s exceptional is the combination of this high snow cover that accumulated in April and May, along with this event with rainfall and warmer conditions,” Lal said. “That’s where the flood comes from.”
Lal said the atmospheric river, which brought moisture from the Pacific Ocean, was “a little harder” to relate to climate change.
La Nina may have played a role in several ways. Although there has been a La Nina like this in the past, “we have never seen in human history constant events in La Nina with such high global temperatures. It’s a unique combination, “Swain said. “We already know that La Nina increases the risk of flooding in some places. Increases the amount of active time in some places. And then you have warmer oceans and a warmer atmosphere that can charge them. ”
“So you really can’t just say it’s one thing or another,” Swain said. “It simply came to our notice then. That’s the natural and the unnatural together. “
A year ago, Montana climate scientists created the Yellowstone Climate Assessment and it warned of rain and snow like this, said co-author Katie Whitlock, a professor of earth sciences at Montana State University.
But the real flood disaster was much worse, she said.
“Who could have predicted that the houses entering the rivers and the bridges would be destroyed,” Whitlock said. “It’s much worse than you think. And this is partly because the infrastructure is not designed for extreme weather events.
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Borenstein reports from Kensington, Maryland; Phyllis of St. Louis.
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