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Vertical Water Temperature in Southern Lake Michigan

One offshore point’s top-to-bottom temperature, nearly every month for the last 26 years

Since 1990, GLERL scientists have been keeping track of the temperature in the middle of southern Lake Michigan. They've been using a vertical chain of instruments that measure temperature from just below the surface to bottom. This is one of the longest vertical temperature records in existence anywhere in the Great Lakes.

Here we’ve plotted the entire dataset for interactive exploration. Click and drag to zoom in on the chart, and hover to see point values.

Notice that temperatures follow a seasonal pattern that repeats yearly. During the summer, water warms and ‘stratifies’, or separates into layers — warmer, lighter water on top, and colder, heavier water on the bottom. Every fall, the lake experiences a ‘turnover’ — a mixing of the layers that results in similar temperatures throughout. Water near the surface cools and becomes heavier, allowing wind to mix it downwards.

Subsurface data is collected on an hourly basis (before 1995 it was every three hours) and is shown here as monthly averages. The approximate coordinates of the sampling location are 42.68013, -87.06567. Surface data comes from NDBC buoy 45007.