File:Spring Thaw across the Great Lakes (MODIS).jpg

English: The spring thaw was sweeping across the Great Lakes of the United States and Canada in mid-April 2023. The Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Terra satellite acquired a true-color image of the seasonal shift on April 13.

A distinct snowline stretches across the image, marking the boundary between warmer air and ground temperatures and the remaining wintery chill. Snow has vanished from most of the ground south of the Canada-United States border, except for the northern portion of Minnesota, Wisconsin, and the Upper Peninsula of Michigan, all south of Lake Superior. No ice remains on any of the Great Lakes—not particularly surprising since ice was scarce all winter. According to the U.S. National Ice Center, the Great Lakes experienced maximum ice coverage for the 2022-2023 ice season on February 4. At that time, the coverage was estimated to be approximately 23. 35%, which is significantly lower than the average maximum of 53% and occurred approximately one month earlier than normal.

Lake Erie stands out among the five Great Lakes, wearing a bright wash of milky blues and greens. The colorful swirls may originate from several sources, such as sediment carried into the lake from rivers and streams. Strong spring winds sometimes churn the water strongly enough to pull sand and silt from the bottom of shallow Lake Erie, where it then floats in suspension. The chalky color may even be due to a whiting event, which is triggered when changes in water chemistry allow the naturally-occurring calcium carbonate normally dissolved in the lake water to precipitate (change into solid form) and become visible. Finally, the greenish tones are suggested of microscopic algae (phytoplankton) blooms, which frequently occur in the lake, but normally emerge as water warms in the summer.