NCAR finds that Boulder’s peak wind speeds are decreasing

DECREASING WIND SPEEDS?

Scientists determine that overall wind speeds in Boulder have decreased since the 1990s

Panel A shows peak gusts from the pre-1995 anemometer and the post-1996 anemometer at NCAR. Panel B shows all reported peak gusts from anywhere in Boulder, compiled anecdotally by Catherine Smith at NOAA. Panel C is a histogram of monthly counts of all peak gusts above 70 mph shown in Panel B. PHOTO COURTESY OF RESEARCH PAPER “EARTH, WIND AND FIRE: ARE BOULDER’S EXTREME DOWNSLOPE WINDS CHANGING?”

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By Olivia Doak

odoak@prairiemountainmedia.com

On Jan. 17, 1982, a massive windstorm in Boulder produced two wind gusts that hit 137 mph and numerous wind gusts reaching 120 mph.

The Daily Camera estimated at the time that at least 40% of all buildings in Boulder were damaged, said Gerald Meehl, a senior scientist at Boulder’s National Center for Atmospheric Research. Houses were quite literally blown apart, he said, resembling hurricane or tornado damage.

“That was kind of the last severe, damaging building (wind) storm that we experienced,” Meehl said.

Meehl said it wasn’t unusual for wind gusts to hit 120 miles per hour in the 1960s, 1970s and 1980s. But now, it’s rare if a wind gust in Boulder breaks 100 miles per hour.

A 2016 Denver TV news story about all-time peak wind gusts in Colorado sparked an idea for a research project after Meehl and his team started thinking that Boulder doesn’t seem to get the same level of high-speed windstorms anymore. The resulting research article determined that wind gusts in Boulder have, in fact, become less powerful in the past 30 years.

“The good news is we don’t get those kinds of severe, damaging gusts anymore, so that’s one message,” Meehl said. “But the other message is it’s still a windy place, so 100-mile-an-hour gusts or 90-mile-an-hour gusts can still cause damage, can cause problems. It’s just not as severe as it used to be, and of course, (fires are) much more part of this than they used to be.”

The last really strong windstorm Boulder saw, he said, was in November of 1995, when peak gusts reached 124 miles per hour. There was not as much structural damage compared to the 1982 windstorm, Meehl said, likely because building codes had strengthened structures and trees had grown bigger.“Since then, we haven’t seen those kinds of windspeeds,” Meehl said.

But, Meehl said, winds in Boulder don’t need to hit record-breaking speeds to be a major problem. During the Marshall Fire, the peak gusts reached about 110 miles per hour, the first peak gust over 100 miles per hour measured at NCAR since 1995.

The NCAR team now needs to do more research to understand why peak wind gusts are less intense. The research article suggests that the diminishing wind gusts may be due to climate change. Meehl said the team will be looking at potential changes in temperature and the atmosphere.

“People say, ‘Oh, well now the winds aren’t a problem anymore because they’re getting weaker.’” Meehl said. “But that’s not the message. We still get peak gusts in the 80s, 90s and low 100s (in miles per hour).”

Winds at any speed can cause damage and spread fire, he said.

One challenge in determining whether the wind gusts themselves had actually changed was the inconsistency in where wind speed measurements were made at NCAR. The elevation and location of NCAR’s anemometers, which measure wind speed and direction, has been in two spots on the roof of NCAR’s Mesa Lab since it opened in 1967. In 1995, the anemometer was moved from a higher elevation on a mast on top of NCAR’s roof to a lower elevation farther east on the roof.

To find out how the change in instrument location impacted wind speed data, NCAR scientists collected data from both locations for three years.

The data collected from 2021 to 2023 showed that extreme gusts were 10% to 16% stronger when measured by the anemometer placed at the higher elevation location on the roof.

“Sure enough, after a few years of recording winds up there, the winds were weaker measured by the weather station anemometer that was lower down on the roof further east, as we expected,” he said. “But even if you factored in a correction for the strength of the peak gust at around 10% you still couldn’t get the strength of the gusts that we saw, like in the ’60s and ’70s that were routinely above 120 (miles per hour).”

The research team also looked at wind reports from other anemometers along the Front Range operated by the National Oceanic and Atmospheric Administration. Those measurements also showed a reduction in peak wind gusts.

Boulder has been and still is a windy place due to its location at the base of the mountains. Because the mountain range is north-south oriented, where winds come from the west, it creates a similar effect of water going over a rock in a stream. The winds gain speed as they flow down the mountains into Boulder.

And, fire is associated with strong winds. Out of 151 windstorms that damaged Boulder from the 1860s to early 1970s, Meehl said, fires were mentioned in connection with the winds in newspaper reports for 57 out of the 151 storms.

“You don’t need 120-mile-an-hour wind to drive a fire that can cause a lot of damage,” Meehl said. “Boulder is still a windy place, we still have this risk of wind-driven fires, but we probably don’t have as big of a risk for damage from the winds themselves as we used to.”