Research from Professor Michael Mann and Ph.D. students Annabelle Horton and Mackenzie Weaver shows that as the worst of these East Coast winter storms intensify, so does their destructive potential—a facet that current coastal risk assessments often ignore.
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In February 2010, Michael Mann was scheduled to come from Penn State to deliver a guest lecture at the Department of Physics and Astronomy—invited by Mark Trodden, then chair of the department and today Dean of Penn’s School of Arts & Sciences. Instead, Mann spent his time in a hotel as a nor’easter blanketed Philadelphia in two-and-a-half feet of snow. “That was the second-highest snowfall event ever for the city,” says Mann, Presidential Distinguished Professor in the Department of Earth and Environmental Science and Vice Provost for Climate Science, Policy, and Action.
Nor’easter tracks for the period 1940–2025. Color scale represents intensities of tracks. The large dotted box corresponds to the domain where the tracking algorithm is applied (20°N to 50°N, 90°W to 40°W), while the smaller dotted box corresponds to the U.S. East Coast region (33°N to 45°N, 80°W to 70°W).
(Image: Courtesy of Michael Mann)
Though the weather prevented Mann from giving his talk 15 years ago, the experience left an indelible mark: “I vowed to eventually look into the impact that climate change might be having on these very powerful storms,” he says.
For several years now, that’s what he’s done, alongside Ph.D. students Annabelle Horton and Mackenzie Weaver, who both begin their third year at Penn this fall. In Proceedings of the National Academy of Sciences, the team has published the results of that research, finding that although the number of nor’easters has decreased since 1940, the strongest of these storms are unquestionably getting stronger, with maximum windspeeds and precipitation rates increasing.
“Standard assessments of coastal risk account for the prediction that we’re likely to see more intense hurricanes, but here along the mid-Atlantic coast, the question of whether we’ll see more intense nor’easters may be as relevant—and the answer appears to be yes,” Mann explains. “Our findings have direct implications for managing coastal hazards.”
Those vulnerabilities aren’t negligible, notes Horton, who studies the history of nor’easters in the distant past using sedimentary evidence unique to these common winter storms. Beyond the significant threat to human life from the storms, which tend to drop massive amounts of rain and snow along the Atlantic coast of the U.S., there are real dollar costs, according to Horton.
“The 1962 Ash Wednesday nor’easter accounted for more than $150 million in damages along the New Jersey coast alone,” she says. “If you look more broadly at the past 40 years of storms, nor’easters can account for $5 to $10 billion of damages along our coastal communities. It’s really important for us to study these storms to understand how they’ll change in the future.”
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