Yellowstone floods reveal flaws in predictions as climate warms | Montana News

By MATTHEW BROWN and AMY BETH HANSON, Associated Press

BILLINGS, Mont. (AP) – The weather forecast for the Yellowstone National Park area on the morning of June 12 looked quite moderate: Warmer temperatures and rain showers would accelerate mountain snowmelt and could produce “minor flooding.” A National Weather Service bulletin recommended moving livestock from the lowlands. areas, but made no mention of danger to people.

As night fell, after several inches of rain fell on a thick layer of spring snow, there was record flooding.

Torrents of water poured down from the mountains. Swollen rivers carrying boulders and trees ripped through towns in Montana over the next few days. The floods washed away homes, wiped out bridges and forced the evacuation of more than 10,000 tourists, park employees and residents near the park.

As a clean-up that is expected to last months continues, climate experts and meteorologists say the gap between the destruction and what was expected underscores a troublesome aspect of climate change: the models used to predict the impacts of storms do not always follow rainstorms, hurricanes, heat waves and other events.

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“These rivers had never reached these levels. We were literally flying blind not even knowing what the impacts would be,” said Arin Peters, senior hydrologist at the National Weather Service.

The hydrological models used to predict floods are based on long-term historical records. But they don’t reflect the climate changes that have emerged over the past decade, said meteorologist and Weather Underground founder Jeff Masters.

“These models are going to be inadequate to deal with a new climate,” Masters said.

Another extreme weather event where models failed was Hurricane Ida, which hit Louisiana last summer and then stalled over the East Coast – inundating parts of Pennsylvania, New Jersey and New York with unprecedented rainfall that caused massive flooding.

The weather service had warned of a ‘serious situation’ that could turn ‘catastrophic’, but forecasts of 3 to 6 inches (8 to 15 centimeters) of rain for New York, New Jersey and Pennsylvania were well below of the 9 to 10 inches (23 to 25 centimeters) that fell.

The killer June 2021 heat wave that scorched the Pacific Northwest offered another example. Warmer weather was expected, but not temperatures of up to 116 degrees (47 degrees Celsius) that toppled previous records and killed an estimated 600 or more people in Oregon, Washington and western Canada.

Yellowstone’s surprise floods prompted an overnight scramble to shut down washed-out roads and bridges, as well as rushed evacuations that missed some people. No one died, somewhat miraculously, as more than 400 homes were damaged or destroyed.

As rainfall-caused landslides began to occur in Yellowstone, park rangers closed a busy road between the town of Gardiner and park headquarters in Mammoth Hot Springs, Wyoming. It was then taken to many places.

The rain and snowmelt were “too too fast and you’re just trying to stay out of the way,” said Tim Townsend, Yellowstone’s deputy chief ranger.

If the road hadn’t been closed, “we probably would have had some fatalities, no doubt,” said park superintendent Cam Sholly.

“The road looks great and then it’s like an 80-foot drop straight into the river,” Sholly said. “No way if someone was driving in the rain at night they would have seen this and could have stopped.”

Rock Creek, which runs through the town of Red Lodge and is normally calm and at times ankle-deep, has turned into a raging river. When the weather service issued a flood warning for the creek, water had already surged over its banks and started to tear down bridges.

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

Red Lodge resident Pam Smith was alerted to the flooding by something banging in her basement before dawn. It was his clothes dryer, floating in the water pouring through the windows.

In a scramble to save memories, Smith slipped on the wet kitchen floor and fell, breaking a bone in her arm. She remembers holding back tears as she walked through floodwaters with her partner and 15-year-old granddaughter to reach their van and get to safety.

“I went blank,” Smith said. “I was angry and I was like, ‘Why didn’t anyone tell us? Why wasn’t there a knock on the door? Why didn’t the police come and- Did she say there was a flood, you need to get out?

Local officials say sheriff’s deputies and others knocked on doors at Red Lodge and a second community that was flooded. But they acknowledged that not everyone had been reached as many rivers and streams overflowed, inundating areas never before known to flood.

While no weather event can be conclusively linked to climate change, scientists said Yellowstone’s flooding was consistent with changes already documented around the park as temperatures warm.

These changes include less snowfall in mid-winter and more precipitation in spring, setting the stage for flash floods when rains fall on snow, said Cathy Whitlock, a climatologist at the State University of Montana.

Warming trends mean spring flooding will increase in frequency – even though the region is suffering from a long-term drought that keeps much of the rest of the year dry, she said.

Masters and other experts noted that computer modeling of storms has become more sophisticated and is generally more accurate than ever. But extreme weather events, by their nature, are difficult to predict, and since such events occur more frequently, forecasters will be much more likely to be wrong.

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

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

This has wide-ranging implications for local authorities and emergency managers who rely on weather reports to guide their disaster response approaches. If they are not warned, they cannot act.

But the National Weather Service is also working to avoid undue alarms and maintain public confidence. So if the service’s models show only low disaster risk, that information is likely left out of the forecast.

Weather service officials said the agency’s actions with the Yellowstone flooding will be analyzed to determine if any changes are needed. They said early warnings that river levels were rising helped officials prepare and prevent loss of life, even if their advisories did not predict the severity.

Computer forecast models are regularly updated to account for new weather patterns due to climate change, Peters said. Even with these refinements, events like the Yellowstone flood are still considered unlikely and often won’t factor into predictions based on what the models say is most likely to happen.

“It’s really hard to balance that feeling you have that it could get really bad, but the likelihood of it getting really bad is so low,” Peters said. He added that the dramatic shift from drought to flood was difficult to reconcile, even for meteorologists, and called it a “weather whiplash”.

To better communicate the potential for severe weather, some experts say the weather service needs to modify its forecasts to inform the public of dangerous low-probability events. This could be accomplished through more detailed daily forecasts or some sort of color-coded system for alerts.

“We’ve been slow to provide this information,” said Gary Lackmann, an atmospheric scientist at North Carolina State University. “You put it on people’s radars and they might think about it and it might save lives.”

Hanson reported from Helena, Montana.

Follow Matthew Brown: @MatthewBrownAP

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