The Great Lakes create unique weather patterns. One of those weather patterns is lake effect snow. Lake effect snowstorms occur in only three places in the world: the Great Lakes, the east shore of Hudson Bay and along the west coasts of the Japanese islands of Honshu and Hokkaido. While people in the snow belt regions have learned to adapt, living near the lakes and experiencing lake effect snow still affects the economy and culture in significant ways. For example, winter sports like skiing and snowmobiling are major industries in some snow areas. This lesson explores how the Great Lakes influence lake effect snow, other factors that contribute to it and ways of reading weather conditions to forecast lake effect storms.
- National Science Education Standards – 5th-8th grade
- Michigan Grade Level Content Expectations – 5th-7th grade
- MS-ESS2-5 Earth Systems: Collect data to provide evidence for how the motions and complex interactions of air masses results in changes in weather conditions.
For alignment, see: NGSS Summary
- Describe the factors that create lake effect snow.
- Describe how differences in lake and air temperature relate to lake effect snow.
- Describe weather conditions associated with the movement of frontal boundaries across the Great Lakes region.
- Describe how hills and highlands help form clouds and precipitation.
- Describe how cities and industrial areas are related to lake effect snow.
Causes of Lake Effect Snowstorms
Weather is caused by large temperature differences between the land and water. (Learn more about the Great Lakes as a heat sink and heat source in the Keeping it Temperate lesson)
During the unstable season on the Great Lakes, the temperatures can change quickly over the land. Here is an overview of how that can happen:
- Mid-August to March: The average temperature of the land is colder than the average temperature of water.
- Mid-November to mid-January: This time of year sees the largest temperature differences between land and water.
- Those temperature differences may average:
- Northern lakes: 30 degrees Fahrenheit (F) (-1 degrees Celsius).
- Southern lakes: More than 15 degrees F (-9 degrees C).
Arctic air, brought down across the lakes by northerly winds can drive temperature differences as wide as 50 degrees F (10 degrees C) in the north and 40 degrees F (4 degrees C) in the south. These temperature differences between the land and water are the source of what we call weather. Arctic air, necessary for lake effect snow, usually comes after a deep low-pressure center has passed through or near the Great Lakes region. As the low pressure center moves through, it opens the way for cold air to rush southward. Cold air usually moves through in the form of a high-pressure area behind a cold front. Snowfall regularly occurs in conjunction with a rising barometer.
Steps to Lake Effect Snow
- Cold air streams across the warm lakes. Air warms and becomes more humid.
- As the air warms, it becomes less dense and rises.
- As air rises, it cools.
- Cooler, moist air may form clouds and cause precipitation.
- After the air has moved some distance over the lake, convection and turbulent exchange have transported the moisture aloft to form clouds. Snow may fall.
- Once over land, moisture in the air condenses into snow. Snow created in this way is called lake effect snow.
- As the warmed air reaches the shoreline, additional lifting may occur as the air begins to “pile up.” Air moves more slowly over land than over water, due to increased friction.
- Hills and high lands on down-wind lake shores force air upward. Air cools further, encouraging cloud formation and greater snowfall.
As the cold air streams across the warm lakes, it is warmed and becomes more humid. As the air warms, it becomes less dense and tends to rise cooling (as it rises). Whenever moist air rises, as previously noted, clouds may form and precipitation may result. Fog results from the intense evaporation or transfer of moisture from the warm water to much colder air when the cold air initially makes contact with warm water. After the air passes from some distance over the lake, convection and turbulent exchange have transported the acquired moisture aloft to form clouds and snowfall may occur.
Large urban areas along the shores of the Great Lakes may, at times, play a role in creating or intensifying downwind, lake effect snowstorms through the additional heat and ice-forming particles they supply.
- Cities: Even small cities are warmer than their surrounding areas. Air is warmed as it passes over urban areas. This warmth may add to the heat acquired from the lakes and may occasionally provide a stimulus for development of lake effect snowstorms.
- Industries: Industries like steel mills emit particles that act as ice-forming nuclei (a particle which acts as the nucleus for the formation of an ice crystal) into the atmosphere. These may encourage snowstorms. The southern Great Lakes region is one of the world’s leading centers for manufacturing iron and steel.
- Automobile exhaust: Lead from automobile exhaust combines with the natural iodine in the air to form lead-iodine compounds. These may also make it possible for ice crystals to grow.
Clues for Predicting Lake Effect Snowstorms
The following are necessary conditions for lake effect snowstorms. Each of the below must be present for a storm to occur:
- Large temperature difference between the lake and air. The greater the difference, the larger the potential for lake effect.
- High pressure cell (rising barometer) following a low pressure cell (falling barometer). This situation provides favorable conditions for lifting the warm, moisture-filled air up for cooling and ice crystal formation.
In addition with one of the following:
- A long ‘fetch’. Fetch is the distance the wind travels over the open water surface. The longer the fetch, the greater the amount of heat and moisture, which may be acquired from the lake. This results in a greater potential for lake effect snow. For example:
- A northwest wind travels almost 130 miles (210 km) across Lake Superior, 150 miles (242 km) across Lake Huron, but only about 30 miles (48 km) across Lake Erie.
- A west-southwest wind travels 30 miles (48 km) across Lake Michigan, 60 miles (97 km) across Lake Huron and nearly 130 miles (210 km) across Lake Erie.
- Or a fetch passing over large industrial areas may also influence lake effect snowstorms. The air receives additional heat and ice-forming nuclei from the particulate matter in smoke and exhaust.
Climate Change in the Great Lakes
The amount of lake effect snow has increased in recent years, likely due to warmer water temperatures and less ice. Increases in temperature may cause areas downwind of the Great Lakes to experience increased lake effect snow, but only if temperatures on land are cold enough to allow snow (rather than rain).
For more information on climate change and lake effect, see: Climate Change Leading to More Snow?
- Examining the Lake Effect
Summary: Students examine lake effect snow in the Great Lakes region, including how to forecast lake effect snow, where it might occur, and what effects it may have on the people of an area.
Time: 50-minute class period
Standards and Assessment
Great Lakes Climate and Water Movement. Earth Systems – Education Activities for Great Lakes Schools (ES-EAGLS). 1996. Series EP-085. Ohio Sea Grant. Ohio State University, Columbus, OH 43212. 33-45. Authors: Fortner, RW, Miller, H, Sheaffer, AL.
Greatest of the Great Lakes (GOGL): A Medley of Model Lessons. 2007. COSEE Great Lakes, Illinois-Indiana Sea Grant, University of Illinois, Champaign, IL 61820 Authors: Goettel, R, Hallesy, T, Murphy, J, White, S, Fortner, R, Stewart, S, Munson, B, Domske, H, Lubner, J, Danielski, A.
Weather and Climate of the Great Lakes Region. 1979. University of Notre Dame Press, Notre Dame, IN. pp. 145-153. Author: Eichenlaub, VL