Note: Lakes Michigan and Huron are treated as one unit for the variables in this section since there is no physical separation between the lake bodies and their ensemble outputs are combined.

Water levels fluctuate on an annual cycle, rising in the spring and summer due primarily to snowmelt runoff and low evaporation rates, and declining in the fall due to high evaporation rates from the temperature difference between the air (cold) and water (still warm from summer months). On average, the highest lake levels on Lake Michigan-Huron are observed between June and August.

Figure 1: Monthly average Lake Michigan-Huron water levels from 1972-2021 (blue) with record highs and lows (black).

Recent years have seen some of the most rapid fluctuations in the recorded history of Great Lakes water levels. Lake Michigan-Huron had a sharp decline in water levels beginning in 1998. Following this decline, the lakes were characterized by an approximately 17 year span of warmer temperatures, low ice coverage, increased evaporation rates, and decreased runoff. A rapid increase in Lake Michigan-Huron water levels began in 2014, a year that coincided with a cold air outbreak, low temperatures, extensive ice cover, and high precipitation rates.  These conditions continued through the end of the decade to reach new monthly record highs in 2020. Following basin-wide dry conditions in early 2021, water levels began declining on Lake Michigan-Huron, but still remained above average at the end of 2021.

Figure 3: A closer look at monthly (blue) and long term average (red) Lake Michigan-Huron water levels from 2012 to 2021, when water levels rose to above average for much of the decade, before declining again. [Click image to enlarge]

Over-lake precipitation totals are expected to increase, on average, due in part to the ability of warmer air to hold more water vapor (moisture) and, hence, increase precipitation. In the 2010s, Lake Huron experienced several years of above-average over-lake precipitation totals. This was the wettest decade on record for the Great Lakes basin, collectively.

Figure 4: Annual (blue) and long term average (red) precipitation totals over Lake Huron from 1972 to 2020.

Lake Huron summer lake surface temperatures increased by an average of 2.9°C (5.2°F) between 1968 and 2002 (Dobiesz and Lester 2009). This can be partially attributed to earlier spring ice melt which allows for longer periods of lake stratification and more exposure to solar radiation (McCormick and Fahnenstiel 1999). Publicly available lake-wide water temperature data only dates back to 1995, so Figure 5 does not capture the long-term or seasonal trends evident from more robust datasets and statistical analysis used in aforementioned studies. It does, however, capture the shift to higher surface temperatures around 1998, that occurred basin-wide.

Figure 5: Annual (blue) and long term average (red) Lake Huron surface water temperatures from 1995 through 2021.

Lake Huron had less ice cover on average during the last 20-30 years compared to earlier years, prior to the 1990s (Mason et al. 2016, Van Cleave et al. 2014). However, there remains strong year-to-year variability, meaning that years with very little ice and years with a lot of ice are still possible. In a warming world, there is less potential for large amounts of ice cover, but there are many forces at play (such as cold arctic air blasts) that can still usher in winters of extreme cold, potentially leading to unprecedented high seasonal mean ice cover (e.g., 2014).

Figure 6: Annual average (blue) and long term average (red) ice cover for Lake Huron from the 1973 ice season to the 2021 ice season. An ice season runs from November 10 the previous year to June 5th of the current year.

These webpages were developed by the GLISA team with funding from National Atmospheric and Atmospheric Administration’s (NOAA) Great Lakes Regional Collaboration Team and Cooperative Institute for Great Lakes Research (CIGLR).

More figures and analysis are available on GLISA’s Lake Huron Climatology page.