DETROIT – Monthly mean water levels continued to set records in September with Lake Superior tying its monthly record high and Lakes St. Clair and Erie setting new record-high September levels.
On Lakes Michigan-Huron and Ontario, water levels remain well above average and near record levels.
In the fall, the lakes generally decline due to an increase in evaporation as temperatures cool off and the cold air moves over the relatively warm lake waters.
During the spring, the lakes tend to rise due to increased precipitation and increased runoff as a result of snowmelt.
We refer to the combined effect of precipitation over the lake, evaporation from the lake, and runoff to the lake as Net Basin Supply (NBS).
This edition of the Water Level Outlook incorporates the projection of water levels if the cumulative NBS over the next 12 months is a repeat of last year (high), near average, or a lower cumulative NBS scenario.