Milwaukee Journal-Sentinel:

Lake Michigan is no longer just a Great Lake; it is a great unknown.

More ominous than the all-time low the lake touched this winter is the fact that it came after languishing for 14 years below its long-term average — another record. And when it did initially drop below that long-term average, it plunged three feet between 1998 and 1999 — yet another record for water lost from one year to the next.

The lake level, of course, has been in constant flux since record-keeping began a century and a half ago. Tracking it on a graph is like looking at an EKG monitor. Little blips and dips reflect seasonal oscillations that cause the lake, in a typical year, to vary about a foot between summertime high and wintertime low.

In addition to those annual ebbs and flows are larger swings that span decades tied to long-term weather patterns, with Lake Michigan’s record high topping out more than 6 feet above the record low set this January.

Draw a red line through the middle of all those highs and lows and you get what was, up until 1999, Lake Michigan’s long-term average surface level — 579 feet above sea level.

That year the lake mysteriously took its 3-foot dive, and it has stayed down for nearly a decade and a half — and counting.