Copyright National Geographic
Winter weather is ransacking the Chicago metro area and parts of Indiana as the region experiences one of winter’s most brutal weather phenomena: lake-effect snow. Heavy snow covered the area Sunday night into Monday morning, with more than a foot of snow recorded by mid-Monday. Lake-effect snow forms when warm, unfrozen lake water and cold air meet. Some of the lake water evaporates into the air, making it warmer and wetter. Once that air moves inland, that moisture cools and turns into snow. If the wind is blowing over large portions of one of the Great Lakes, the storm system will take in more water. The greater the temperature difference between the winds and water, the more moisture is absorbed into the atmosphere. This type of snow storm is most common in the Great Lakes region because of their large size and location near populous cities. However, National Weather Service meteorologist Zachary Yack says this weather can occasionally happen near smaller alpine lakes. Lake-effect snow also occurs in Japan as cold air moves across the Sea of Japan, says Colgate University geography professor Adam Burnett. But as the planet warms, will we continue to see major Midwestern snow storms? Here’s the science behind this phenomena and how climate change could make these storms more intense in the short term. National Geographic History Magazine The gift that brings the past to life - now with a free tote What is lake-effect snow? Moisture is the fuel that drives lake-effect snow. When cold air blows over a warm surface, that balmy temperature causes the cold air to heat up and rise. As that warm, humid air rises, it pumps clouds full of more precipitation. When those clouds blow inland, frozen lake water suspended in the atmosphere falls to the ground as heavy snow. Burnett explains that, as the seasons change, water cools down at a slower rate than air temperatures. “So you end up with a situation where the Great Lake water temperature is a lot warmer than the air that's moving over the lakes, and that's what sets up lake-effect precipitation.” (The 'least spectacular' of the Great Lakes is a devastating snow machine.) “This storm is somewhat unique because it had some moisture from the broader system of air, plus the moisture off the lakes,” Yack explains. But he says that most lake-effect cases are generated primarily off the lake moisture itself. Yack says that the cold air mass present over the Chicago area is causing an unstable layer of cold air to form over an unusually warm Lake Michigan, which had water temperatures in the upper 40s to low 50s. In October, the lake’s average surface temperature was around 4.5°F degrees higher than the 30-year average of about 57°F, according to data from the National Oceanic and Atmospheric Administration. Simultaneously, temperatures in the atmosphere are exceptionally cold. “Temperatures logged were near record for this time of year,” Yack said. “Our morning observations had a temperature of -42°F at 180,000 feet while the record for this time of year is -30 to -35°F at that altitude.” Because the storm is driven by narrow bands of wind, some people may not see snow at all while others might see intense snowfall rates of over 2 to 3 inches per hour. “It's just a very small scale feature, so depending on where the band sets up, some areas may see a lot of snow like we saw yesterday. But some areas don’t see as much because they’re too far inland or maybe the band just happens to stay away from that location,” Yak explains. Will a warmer planet make lake-effect snow storms worse? When Burnett first published a paper on the relationship between climate change and lake-effect snow in 2003, he predicted that warmer water in the Great Lakes would lead to more of these midwestern snow storms. “It looked like the snow record was pointing in that direction,” Burnett says. “But when I looked at it a little more closely, I found that reality is a little more complicated.” What’s missing? Cold air. While warmer waters are persistent, Burnett explains that we are increasingly missing the cold air that moves across that warm water and triggers the snow process. (Ocean temperature is rising. Here's why even small increases have massive effects.) “The propensity for cold air to move across the Great Lakes has become somewhat less frequent as global warming has occurred,” he says. “Now, when we get cold air across the warm lakes, we get big lake-effect snow storms. But if you don't have the cold air, you're not going to get lake-effect snow.” Despite an increase in rain in the Great Lakes region, the overall amount of snowfall is likely to decrease, according to an assessment of the impacts of climate change on the Great Lakes that was updated this year. The assessment found that warmer temperatures, reduced lake ice cover, and enhanced evaporation may lead to increased lake-effect snowfall in the short-term. Southern lake-effect zones may see lake-effect snow replaced by lake-effect rain, as winter temperatures will warm and be less suitable for snow. “The models all suggest that in the short run, maybe we'll get more lake-effect or lake snow, but eventually the air just becomes too warm and it all becomes mostly rain,” Burnett explains. While some may cheer at less snowfall, Burnett says he is concerned about what less snow means for the hydrologic conditions of the area. Typically, temperatures are cold enough to allow snow to pile up and stay throughout the winter months. During the spring, temperatures will rise and these mounds of snow will begin to melt, allowing large swaths of water to runoff into local creeks, streams, and rivers, revitalizing aquatic ecosystems and soil. Now, as winter snow diminishes, experts are concerned about the ripple effects of this precipitation cycle. “We don't have the snow collection that occurs over the winter. It snows, it melts. It snows, it melts. It snows, it melts,” Burnett says. “All of the water that comes from these little melts runs into the streams and rivers, but it's not there in the bulk of spring, which changes the soil moisture conditions and not necessarily for the better.”
