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Yellowstone floods reveal errors in forecasts as climate warms: NPR

A home sits in Rock Creek after floodwaters washed away a road and a bridge in Red Lodge, Mont., on June 15, 2022.

David Goldman / AP


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A home sits in Rock Creek after floodwaters washed away a road and a bridge in Red Lodge, Mont., on June 15, 2022.

David Goldman / AP

BILL, Mont. – The weather forecast for the Yellowstone National Park area for the morning of June 12 looks pretty good: warmer temperatures and showers will cause mountain snow to melt faster and possibly cause “minor flooding” . A National Weather Service bulletin recommended moving livestock from low-lying areas but made no mention of the danger to people.

As night fell, after several inches of rain fell on the deep spring snow and ice, there were devastating floods.

Streams of water flow from the mountains. Brimming rivers carried crumbling rocks and trees through towns in Montana over the next few days. The floods swept away homes, swept away bridges and forced the evacuation of more than 10,000 tourists, park staff and residents near the park.

Climate experts and meteorologists say the gap between devastation and what is forecast reveals a complex aspect of climate change: heat waves and other events.

Arin Peters, senior hydrologist with the National Weather Service, said: “Those rivers have never reached that level. We’re really flying in the dark without even knowing what the impact will be like. how”.

Hydrological models are used to forecast floods based on long-term, historical records. But they do not reflect changes to the climate that have emerged over the past decade, said meteorologist and Weather Underground founder Jeff Masters.

“Those models won’t be able to cope with the new climate,” Masters said.

Another extreme weather event for which short-term patterns appear was Hurricane Ida, which made landfall in Louisiana last summer and then stalled over the South China Sea – bisecting parts of Pennsylvania, New Jersey and New Jersey. York with unprecedented rainfall caused major flooding.

The weather agency has warned of a “severe situation” that could turn into a “disaster,” but forecast 3 to 6 inches (8 to 15 centimeters) of rain for New York, New Jersey and Pennsylvania lower. much more than the 9 to 10. inch (23 to 25 cm) level has decreased.

The deadly June 2021 heatwave that scorched the Pacific Northwest is another example. Forecasts for warmer weather, but not temperatures of up to 116 degrees (47 degrees Celsius) toppled previous records and killed about 600 or more people in Oregon, Washington state and western Canada.

Unexpected floods in Yellowstone prompted a nighttime scramble that closed roads and bridges being swept away by water, plus hasty evacuations left some people missing. No one was killed, somewhat miraculously, as more than 400 homes were damaged or destroyed.

A road ends as floodwaters wash away a house in Gardiner, Mont., on June 16, 2022.

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A road ends as floodwaters wash away a house in Gardiner, Mont., on June 16, 2022.

David Goldman / AP

When precipitation-induced rock slides began to occur in Yellowstone, park rangers closed a heavily used road between the town of Gardiner and park headquarters in Mammoth Hot Springs, Wyoming. After that, it was washed away in many places.

The rain and snow melt “so fast and you just have to try to stay away,” Yellowstone Deputy Sheriff Tim Townsend said.

If the road hadn’t been closed, “we’d have had deaths for sure,” without a doubt,” said Park Superintendent Cam Sholly.

“The road looked absolutely fine and then it was like an 80-foot drop into the river,” said Sholly. “It’s impossible if someone was driving in the rain at night that they could have seen that and could have stopped.”

Rock Creek, which runs through the city of Red Lodge and is normally very calm and sometimes just ankle deep, has become a raging river. When the weather agency issued a flood warning for the creek, the water overflowed its banks and began to knock down bridges.

By the time the warning was issued, “we knew it was too late,” said Scott Williams, commissioner for Carbon County, Montana, which borders Yellowstone.

Red Lodge resident Pam Smith was warned of flooding by something pounding around her basement before dawn. It was her tumble dryer, floating in the water that spilled through the window.

During a scramble for mementos, Smith slipped on the damp kitchen floor and fell, breaking a bone in his arm. She recalls crying as she and her partner and 15-year-old niece made their way through floodwaters to their pickup truck and drove to safety.

“I’m empty-handed,” Smith said. “I got angry and said, ‘Why didn’t anyone warn us? Why is there no knock on the door? Why didn’t the police come around and say there’s a flood, you need to get out? “

Local authorities said sheriff’s deputies and others knocked on doors at Red Lodge and a second community was flooded. But they concede that not everyone can reach it because countless rivers and streams have overflowed, swampy areas that have never been flooded before.

While no weather events can be conclusively linked to climate change, the scientists say the Yellowstone flooding is consistent with the changes that have been recorded around the park as temperatures increase. Warming.

Those changes include less snowfall in the middle of winter and more rainfall in spring – setting the stage for flash floods when rain falls on the snow, said climate scientist Cathy Whitlock of Montana State University. .

The warming trend means spring flooding will increase in frequency – even if the region suffers from a prolonged drought that leaves much of the rest of the year dry, she said.

Masters and other experts note that computer models of hurricanes are becoming more complex and generally more accurate than ever. However, by its very nature severe weather is difficult to predict, and since such events occur more frequently, there are more opportunities for forecasters to get it wrong.

The rate of the most extreme rainstorms has increased fivefold, Masters said. So an event with a 1% chance of happening in any given year – often referred to as a “one in 100 years” event – now has a 5% chance of happening, he said.

“We’re literally rewriting our weather history book,” said Jason Furtado, professor of meteorology at the University of Oklahoma.

That has broad implications for local governments and emergency officials, who rely on weather reports to guide their disaster response methods. If they are not warned, they cannot act.

But the National Weather Service also tries to avoid undue alarm and maintain public confidence. So if the service’s models only have a very small probability of disaster, that information is likely to be out of the forecast.

Weather service officials said the agency’s actions with the Yellowstone flooding will be analyzed to determine if changes are needed. They said early warnings that river levels were rising helped officials prepare for and prevent loss of life, even if their advisors failed to predict the severity.

Computer-based forecasting models are regularly updated to account for new meteorological trends due to climate change, Peters said. Even with those improvements, events like the Yellowstone floods are still considered low probability and therefore would not normally be included in forecasts based on what models say are more likely. out most.

“It’s really hard to balance the feeling you’ve got that this could get really bad, but the chance of it getting really bad is very small,” says Peters. He added that the dramatic change from drought to flood was difficult even for meteorologists to reconcile and called it a “weather storm”.

To better inform the possibility of severe weather, some experts say the weather agency needs to change its forecast to inform the public about low-potential hazardous events. . That could be done through more detailed daily forecasts or some kind of color coding system for the alerts.

“We were slow to provide that information,” said North Carolina State University atmospheric scientist Gary Lackmann. “You put it on people’s radar and they can think about it and it can save lives.”

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