2020-Aug-16
August 16 Water Levels Report
So far this month, the Great Lakes Basin as a whole has accumulated 114% of its historical average rainfall.
Water levels continue to be well above average and near or above record high levels. From a month ago the water level on Lake Superior is up 3 inches, Lakes Michigan-Huron is unchanged, and St. Clair, Erie & Ontario are all down 4 inches. Lakes Superior, St. Clair, Ontario, & Erie are lower by 1, 1, 2 & 19 inches, respectively, and Lakes Michigan-Huron is 4 inches higher than it was at this time last year. Lakes Superior, Michigan-Huron, St Clair, Erie & Ontario are 11, 34, 31, 27 & 7 inches, respectively, above their long term August average. Lakes Michigan-Huron is 2 inches higher than it’s previous record high for August. All the other lakes are at or below their August record high.
In a month’s time, the level of Lake Superior is expected to be unchanged, and Lakes Michigan-Huron, St Clair, Erie & Ontario are expected to be down between 1 and 6 inches. Outflows from Lake Superior into the St. Mary’s River and Lake Michigan-Huron’s outflow into the St. Clair River are predicted to be above average for this month. Lake St. Clair’s outflow through the Detroit River and Lake Erie’s outflow through the Niagara River are also forecasted to be above average in this month. In addition, Lake Ontario’s outflow through the St. Lawrence River is projected to be above average for this month.
High water levels and potentially record high water levels are expected to persist for at least the next six months, so flood prone areas are expected to remain vulnerable.
With regard to the forecast graph below, and the more recently updated first graph in this report, the USACE is predicting that the most likely outcome is that levels will not go up any further this year, remain much the same as they are now (about 3-4 inches higher than last year) through August, and then start to decline in September.
Please note that the purple and blue lines, and dotted lines, in the USACE forecast graph show what happened with water level changes from month to month in each of the years 1986-87, 1977-78, 1930-31 and 1976-77 – they do not represent actual water levels in those years.