Persistent afternoon thunderstorms have battered northern Vermont’s farms, washed out roads, and brought Lake Champlain to record levels over the last few weeks. The high waters of Lake Champlain, unprecedented at this time of year, can be linked to climate change, scientists say.
“With the data and with the research, you can say that this weather pattern we have right now is definitely the fingerprint of climate change,” said Roger Hill, a consulting meteorologist who does weather forecasts for utilities in the state as well as several radio stations.
The weather pattern Hill is talking about is a mass of moist, tropical air from the Gulf of Mexico that has been forced up into the Northeast by a high pressure zone over the western United States, another high pressure zone over the Atlantic, and a low pressure trough over the central United States. The Bermuda High, the zone over the Atlantic, blocks weather patterns from moving east, away from Vermont.
“That trough that’s off to the west over the U.S. is what’s unusual—to lock in and stay there for such a long period of time,” said Hill. Typically, the jet stream moves in short waves, perhaps the size of Montana and Wyoming, across the United States, and it does so relatively quickly. “But what’s happening is the big, long meandering jet stream that snakes way down into the Gulf of Mexico from Canada, it picks up that tropical moisture and displaces it way north. That’s what’s making the weather crazy. And it’s stuck, it can’t get anywhere.”
On July 4, the water level in Lake Champlain exceeded the all-time record for that day, topping out more than three feet above average at 99.38 feet, as recorded at the King Street dock in Burlington. Since then, the water rose to a record 99.64 feet on July 8 before declining slightly—but still breaking records—at 99.59 feet on July 10. The National Weather Service has been keeping records there since 1908.
Conor LaHiff is a meteorologist at Burlington’s National Weather Service office. He agreed that this weather pattern is unusual. “The amount of time it’s spent over us is abnormal. We’ve been in this airmass for two weeks at this point.”
The last time the lake flooded was in the spring of 2011. The Lake reached its highest recorded level at 103 feet and caused widespread damage in Quebec and in communities along the lake in New York State and Vermont. Estimated road damage in Vermont alone was $6 million.
“Typically during the spring months — anywhere from the mid part of March to mid-June—Lake Champlain is at its highest and that’s due to snowmelt and spring showers,” said LaHiff. Then the lake level falls throughout the summer. “The difference this year is that we’ve had record levels of rainfall across the state and parts of New York for both May and June, which have kept that water level abnormally high.”
Vermont has had more than 11 inches of rain above average for May and June. The two months are the wettest consecutive 30-day periods on record for Vermont.
“If you go back 30 or 40 years, we had weather patterns where, typically, our fronts would pass us every five days or so and there would be a strong flow from west to east,” said Alan Betts, an independent climate researcher based out of Pittsford who is a consultant for NASA and the National Oceanic and Atmospheric Administration. “But if you look at the last few years, there’s been a pattern where the amplitude of the jet stream has got stronger and the jet stream has been moving more slowly from west to east. That has changed how long periods of no rain or periods of rain remain over us.”
LaHiff said July 13 was the start of a drier period as the Bermuda High breaks down and the low-pressure trough moves into our region. He said we could still see some rain, but the humidity will drop.
“The way to think about jet streams and frontal systems and storms is that broadly speaking the tropics are warm and the Arctic is cold,” said Betts. “These global weather patterns are transporting heat and they’re transporting water from the tropics further north, trying to keep the earth in some sort of energy balance—and they do. But as the Arctic is melting and getting warmer, that gradient of temperature between the tropics and the Arctic is getting less. It appears that the northern hemisphere climate patterns, patterns of the jet stream, are changing as well, and that’s affecting how our climate is changing.”
A 2012 Rutgers University study led by Dr. Jennifer Francis found that the jet stream, a current of high-altitude air that curves across the northern hemisphere, is becoming unstable, curvier, and slower. The result is an increase in extreme weather events that stay in place longer, such as persistent storms that cause flooding, or long-lasting drought. Francis found connections between anomalies in the jet stream and a number of extreme weather events throughout the world.
“It’s why we’ve had 500-year floods in Europe. It’s why Calgary had the biggest floods in the history of Canada,” said Hill. “It’s happening all over the world and it’s all related to these weather patterns that are meandering.”
LaHiff is not so certain, though he agrees the Rutgers study is convincing. “It’s not a definitive answer as to why some of this stuff is happening,” he said, “but it certainly does make sense.”