For the first time in about 25 years, the water level of the all the Great Lakes is above normal. Lakes Superior, Michigan and Huron are about 5 inches above the long term average.
This ends a 15-year period where lake levels have been below historic averages.
Lakes Huron and Michigan were at record low levels in January 2013; that is a rapid rise in water level to be above normal two years later. Such a rapid increase has not been measured since observations began in the mid-1800s.
The water levels of the Great Lakes are determined by the amount of water flowing in and out of the lakes.
Precipitation, runoff, and water from streams and groundwater supply water to the lakes, while evaporation and water flowing out of the Great Lakes system are water losses.
When the input exceeds the output, the levels rise.
The water cycle of the lakes is complex, and weather has played a role in this turnaround in lake levels.
Above-average precipitation and above average runoff in the Great Lakes watershed, particularly in the springs of 2013 and 2014, helped to restore lake levels.
The frigid winter of 2013-2014 also helped by reducing evaporation.
Ice on the lake and cold waters reduce evaporation, which also reduces snowfall in the snow-belt regions of the lakes.
Information on and forecasts of Great Lakes water levels is available from several agencies in the United States and Canada.
The forecast for the water levels is to continue to be above average, though levels could change relatively quickly.
