If you have never been on the shoreline of a Great Lake when the lake-effect-snow-making machine cranks up, then you have missed an exciting weather experience. Most people don’t like snow, especially when it is coming down in a white-out event. However, the experience can be intense, as long as you don’t have to drive. (Note: See more information about lake-effect snow below.)
Lake-effect snow has certainly hit the Grand Marais area this past few weeks. Pictured below are some shots I took on January 26th during a snow-shoe from the Sable Visitor’s Center, along Sable Falls (Second) Creek, to the Lake Superior shoreline and back. In the summer, you can complete this 2.8 mile round-trip hike in an hour or so. In the deep snow, it took me almost 3 hours! It was grueling and more of a work out than I bargained for, but it was worth it!
The first picture is of Sable Falls Creek, about half-way between the visitor’s center and the falls. In some places, the river’s current creates enough friction to prevent freezing, while in other places the river completely freezes over. Note “Casper” hanging on the branch in the lower right hand corner of the first picture. In places where the river is frozen over, beautiful ice swirls can form from the influences of the river’s current.
Compare the picture of Sable Falls below, with the one included in the fall. What a difference! The heavy snows and cold temperatures definitely created this natural ice sculpture!
Because I have been busy, I have not had time to get down to the beach since before the lake-effect snows began. I wasn’t sure what to expect, especially since people were finding agates only a few weeks ago. No longer. Not only does the snow pile up on the beach, but the snow that falls into the lake sometimes forms slush, which is piled up into icebergs by the waves. This picture was taken right at the mouth of Sable Falls Creek, looking west toward the Log Slide. You can see the first row of icebergs that have formed just off-shore. Some of them are already almost 20 feet tall. This could be a great year for big picturesque icebergs! That is good news for all you rockhounds. Once they form, icebergs can break off with a stiff south wind, get blown to distant beaches, gouge up rocks as they are shoved to shore, break off again with another change in wind direction, and end up deposited on our beach in the spring to melt with their new load of rocks.
Lake-effect snow occurs when you have a cold air mass that blows over a large body of water with a significantly warmer temperature. A convection occurs wherein the warmer air with its moisture rises. As it rises, the water vapor condenses to form clouds. As the clouds reach the colder landmass downwind, the moisture is squeezed back out of the clouds in the form of snow.
Lake-effect snow squalls occur during late fall and early winter when cold arctic air blows over long expanses of warmer lake water. The areas that receive lake-effect snow are called snow belts. Although this weather phenomenon occur at several places in the world, it is best known on the southern and eastern shores of the Great Lakes.
There are several characteristics that impact lake-effect snow:
- Temperature Difference: To produce lake-effect precipitation, the temperature of the air mass must be significantly colder than the temperature of the water. The greater the difference, the more the instability and the higher the potential for developing snow. Usually the temperature difference must be at least 30 degrees to create lake-effect precipitation.
- Fetch: The fetch is the distance across the lake that the air mass moves. The greater the distance, the more chance there is for heat energy and moisture to transfer from water to air, thus, increasing the amount of precipitation that can be produced. Usually the fetch must be at least 60 miles to produce lake-effect precipitation.
- Wind Shear: Wind shear refers to variation of wind speed or direction. When there is a weak directional shear (less than 30 degree change of direction), well organized bands of clouds form resulting in greater amounts of lake enhanced precipitation. If the directional shear is between 30 and 60 degrees, weak lake-effect bands are possible. If the directional shear is greater than 60 degrees, nothing more than flurries is usually produced.
- Wind Speed: The higher the wind speed, the farther inland will be the potential for lake-effect snow.
- Topography: The speed of wind offshore can be nearly double the wind speed observed onshore. This is caused by the differences in friction between land and water. When wind is blowing over water, there is less friction compared to when wind blows over land. Thus, the more complex the topography is onshore, the more friction there is, and the more the wind is slowed down which can increase the amount of lake-effect precipitation. Also, the higher the elevation on shore, the more the moisture is squeezed out of the lake-effect clouds.
- Ice Cover: As the lake gradually freezes over, the potential for lake-effect snow is lessoned. This occurs because the liquid surface of the lake shrinks reducing the potential for transferring heat and moisture to form lake-effect clouds. Also, as the lake temperature drops, the temperature difference between the lake and the air mass decreases, thus, reducing the instability and limiting the energy that can “fuel” the lake-effect machine.
The amount of lake-effect snow produced depends upon all of the factors listed above. If the conditions are right, up to 10 inches of snow have been known to fall per hour. This month in Grand Marais, we have received almost three feet of lake-effect snow. One of the record lake-effect snow events ever recorded occurred in Buffalo, NY between December 24th and 28th, 2001 during which 82.3 inches of snow fell!
The impact of the lake-effect machine can especially be seen in the Lake Superior region. Snowbelt areas in the Keeweenaw and near Grand Marais average over 250 inches of total snowfall each year. Duluth, MN, which is not impacted by lake-effect due to its proximity on the western shore (protected from the predominant northwest winds), averages only around 77 inches per year. Also, in any single storm, Grand Marais can receive a dozen or more inches of snow, while Seney, located 25 miles to the south, receives none.