By Peter J. Sousounis, The University of Michigan

Exactly the right ingredients

While many states across the northern tier of the US can boast large quantities of snow in the winter, the Great Lakes region is truly unique when it comes to winter weather. First, the fact that the lakes are large and close together means that arctic air is significantly warmed and moistened as it crosses over the relatively warm water in winter. The lakes are big enough so that they supply considerable moisture but small enough so that the air remains cold enough for snow. Second, the continental location means that the Great Lakes region as a whole typically wouldn't get nearly as much precipitation in winter as ones that are closer to the East and West Coasts of the US were it not for the Great Lakes. Third, the mid-latitude location of the region virtually ensures that the weather remains warm enough in all but the coldest of winters so that the lakes don't entirely freeze but also ensures that it gets cold enough for snow to fall in even the warmest of winters -- even after the air has been warmed additionally by the lakes.

 

All these factors mean that areas in the Great Lakes region can get a lot of snow when the temperature is cold enough -- even without any large-scale storms nearby. The type of snow that occurs during these cold air outbreak conditions is called lake-effect snow. This snow usually falls in narrow (10 km wide) bands. At any given time there may be one or more of these bands present. Areas on the south and east (e.g. downwind) sides of the Great Lakes are usually hit hardest. Places like Traverse City, Michigan, for example, receive nearly 100 inches of their annual snowfall total (120 inches) from lake-effect snow. While strong cold northwesterly flow usually generates the most intense lake-effect snowstorms, wind from any direction across the lakes can significantly enhance the snowfall along the downwind lakeshores. Places like Duluth, Minnesota, Green Bay, Wisconsin, and Chicago, Illinois, for example, can get significant lake-enhanced snow as low pressure systems churn their way northeastward through the lakes region and cold northeasterly winds blow across Lakes Superior and Michigan.

Winter fun
While snow can be a real headache -- especially in areas that are unprepared -- many residents take advantage of the unique weather conditions (sometimes fresh snow can fall continuously for several days at a time up to a week!). Snowmobiling, cross-country and downhill skiing, sledding, ice fishing, ice sailing, and ice-skating are popular winter pastimes in the Great Lakes region. The Upper Peninsula of Michigan, for example, is well known for some of the finest downhill skiing in the entire region. Many lakeshore communities depend on cold conditions during the winter to boost the local economy. When lake-effect snow conditions are unfavorable, these local economies are significantly affected. According to Stanley Changnon, Emeritus Chief of the Illinois State Water Survey, business at Midwestern ski resorts was  down 50% and losses were estimated at $120 million during the 1997-98 winter, when El Nino was in full swing.

A changing pattern
Recent simulations from the Canadian Model (CGCM1) and the United Kingdom Hadley Model (HadCM2) suggest that the climate in the Great Lakes region by the end of the 21^st century will be warmer and wetter -- with the CGCM1 being warmer and drier than the HadCM2 (4 vs 2°C and 25% increase vs 50% increase). While understanding the mean temperature and precipitation changes predicted by the models is important, day-to-day weather will be affected by corresponding changes to cyclone tracks, arctic outbreaks, and lake-effect snow patterns. In predicting these crucial day-to-day local aspects of the weather, even the current suite of GCMs is inadequate. However, some conclusions about the local weather patterns can be made with confidence by understanding the connection between the large scale flow patterns and local weather. In this respect, both models are more similar and suggest that by the end of next century, the typical winter may be comparable to what we experience now during a moderate-to-strong El Nino. The coldest winters may be comparable to what we experience now in a normal winter. Snowfall totals may therefore be half the current normal totals with lake effect snow being significantly reduced, especially over the southern portions of the region where average temperatures barely support snow now. Both the CGCM1 and the HadCM2 suggest a more zonal flow pattern, meaning more Pacific systems, fewer Gulf of Mexico systems, and fewer Alberta Clippers. Alberta Clippers are a primary source for reinforcing the cold air over the Great Lakes in winter. Fewer outbreaks likely means less lake-effect snow.

Impacts on recreation
Less lake-effect snow could potentially have a considerable impact on the winter recreational activities of the region -- particularly in the southern portions, where significant reductions in snowfall totals coincide with populous urban centers like Chicago, Detroit, Cleveland, and Buffalo. People in these regions currently require only short excursions to reach the snow and can therefore take advantage of it frequently during the winter.   However, if a 5 to 6 hour drive is needed to get to the snow, people may not be taking advantage of it so frequently. This inconvenience translates to fewer cold-weather recreation outings per winter, which will impact local economies as well as people's physical and mental well-being. Unfortunately, while it may become too warm for snow, it will still be too cold for people to switch to other (typically summertime) recreational activities such as camping, golfing, and bicycling. More people may find themselves stuck at home and there may be more incidences of Seasonal Affective Disorder - a SAD state of affairs indeed.

For more information, contact:
Peter Sousounis, AOSS Department, The University of Michigan; Ann Arbor, MI 48109; phone (734) 936-0488; email: sousou@umich.edu