Damaging thunderstorm winds increasing in central U.S.

Destructive winds that flow out of thunderstorms in the central United States are becoming more widespread with warming temperatures, according to new research by the U.S. National Science Foundation-supported National Center for Atmospheric Research (NCAR).

The new study, published in Nature Climate Change, shows that the central U.S. experienced a fivefold increase in the geographic area affected by damaging thunderstorm straight line winds in the past 40 years. The research uses a combination of meteorological observations, very high-resolution computer modeling and analyses of fundamental physical laws to estimate the changes in the winds, which are so short-lived and localized that they often are not picked up by weather stations.

The work was funded by NSF, which is NCAR's sponsor, and by the Massachusetts Institute of Technology Climate Grand Challenge on Weather and Climate Extremes.

"Thunderstorms are causing more and more of these extreme wind events," said NCAR scientist Andreas Prein, the author of the study. "These gusts that suddenly go from no wind at all to gusts of 60 to 80 miles per hour can have very damaging impacts on buildings, power grids and even human safety."

Straight line winds are caused by powerful downdrafts that flow from the base of thunderstorms. The National Weather Service classifies such winds as damaging if they exceed 50 knots, or about 57 miles per hour. The winds likely cause about $2.5 billion in damage annually in the U.S., based on insurance industry estimates.

Scientists have long been interested in the impact of climate change on straight line winds. Until now, however, simulations of climate conditions run on computer models have been too coarse to capture such brief and small-scale events. Further clouding the picture, weather observations appear to show that there are more periods of little to no wind worldwide (a phenomenon known as global stilling), even though, paradoxically, maximum wind speeds can rise simultaneously.

To determine if damaging straight line winds are becoming more widespread, Prein turned to a high-resolution computer model simulation that NCAR scientists recently produced in collaboration with the U.S. Geological Survey. The advanced simulation, named CONUS404, simulates climate and hydrological conditions at a resolution of 4 kilometers (2.5 miles) across the continental U.S. over the past 40-plus years.

Prein focused on summertime conditions in the central U.S., a global hotspot for straight line winds. The high-resolution modeling enabled him to get a much more fine-grained picture of winds than relying on sparse atmospheric observations, and to expand his analysis from 95 weather stations to 109,387 points in the simulation. The simulation showed that the area affected by straight line winds has increased in the last 40 years by about 4.8 times.

"As these findings show, it is crucial to incorporate the increasing risk of straight line winds when planning for the impacts of climate change so we can ensure the future resiliency of infrastructure to this frequently neglected peril," Prein said.