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UWM forecasters de A question about OSHA regulations may have led to a revolution in weather forecasting. In 2016, UWM’s Innovative Weather Center, a student-staffed agency that provides custom forecasts, was soliciting the Milwaukee Brewers as a possible client. The Brewers’ stadium features a retractable roof. When it opens or closes, the team needs staff members up high to oversee the operation. But OSHA has strict guidelines about the wind conditions that workers may be exposed to. The Brewers wanted to know: Could Innovative Weather predict peak wind gusts around the ballpark? “I looked into it and learned that not only do I not know how to forecast wind gusts, but nobody knows,” said UWM atmospheric sciences professor Jonathan Kahl. “There’s no consistency in the available methods and there’s no testing of the accuracy of those methods.” Kahl is not affiliated with Innovative Weather, though he works closely with the UWM faculty members who run the organization. After the Brewers posed their question, Kahl and Austin Harris, his Master’s student at the time, set to work to find a model that could answer it. Filling in the missing data
Wind spins the city of Milwaukee wind turbine at Port of Milwaukee. Photo courtesy of the Milwaukee city government. 6 • IN FOCUS • March, 2021
Wind gusts are caused by vertical air movement when fast-moving air high in the atmosphere moves downward toward the earth, bringing its momentum with it. Because they’re over so quickly and because scientists can’t easily measure vertical wind speed, it’s hard to predict the top speed of a wind gust.
Jonathan Kahl
To do so, scientists have compiled historical and current data from weather stations around the world to build models to estimate gusts, but there’s a problem with that information. “In the standard hourly weather reports that operational forecasters use … the reported wind speed is the average wind speed during only two minutes of the hour. The wind gusts are only reported if certain criteria are met. If the wind gust is reported, it refers to wind gusts during only 10 minutes of the hour,” Kahl explained. In other words, it’s likely that scientists are missing the strongest wind gusts. So, to build his forecasting model, Harris had to gather minute-byminute historical wind speed data for Milwaukee – 60 measurements an hour; 1,440 measurements a day; 525,600 measurement per year; and over 4 million measurements for eight years’ worth of data.
