Michiganders making their way to Lake Michigan’s shorelines this weekend might notice the water is a bit colder than usual.
A natural weather phenomenon known as an upwelling event caused colder water from deeper parts of the lake to move toward the surface, leading to a sharp drop in temperatures at beaches across parts of West Michigan.
Water temperatures along Lake Michigan's shoreline showed a dramatic contrast Thursday afternoon, with some beaches seeing temperatures in the 70s while others remained in the 40s following the upwelling event.
At South Haven Beach, water temperatures reached about 73 degrees, while other locations that were affected more by the upwelling continued to report much colder conditions, with some areas still seeing temperatures in the 40s.
Scott Thomas, a meteorologist with the National Weather Service, said the event was caused by stronger winds from the north that lasted fora period of time.
Upwelling happens when those winds interact with the lake and push surface water near the coastline farther offshore. As the warmer surface water moves away, colder water from deeper in Lake Michigan rises to replace it.
"When that happens, because of the way the wind interacts with the lake, that takes the lake water that's right along our coast offshore," Thomas said. "So cooler water from deeper in the lake then comes up to replace it."
The shift in water movement can cause temperatures to change quickly. During this week's event, some locations saw water temperatures fall into the 50s, while others experienced even colder conditions.
"In this case, we saw them get down to the mid-50s, or in the case of Ludington, even in the low 40s,"
Thomas said.
While the sudden drop in temperatures may be surprising for people spending time along the lake, Thomas said upwelling events are not unusual for Lake Michigan.
"These do happen on occasion," Thomas said. "They can happen on average a couple times a year. They're not rare, but they're not common."
The length of an upwelling event depends on how long the weather pattern that causes it remains in place.
According to Thomas, the most important factor is whether winds continue coming from the north.
"So, how long upwelling events last depends on how long those winds from the north stay in place," Thomas said.
If those winds remain steady, colder
water can continue to move upward and keep shoreline temperatures lower for a longer period of time. But when wind patterns change, conditions can begin to shift quickly.
In this case, the event was relatively short-lived because the winds changed direction.
"It ended up being a shorter duration event because we had the winds from the north going into yesterday that have switched back to southwest today," Thomas said.
The change in wind direction has already allowed water temperatures to begin recovering.
"We're starting to see water temps rewarm," Thomas said.
On Thursday morning, temperatures along the stretch of Lake Michigan monitored by the National Weather Service ranged from the mid-50s at the coldest locations, including Holland, to the low 70s at Duck Lake. Many other locations were reporting temperatures in the 60s.
Even as temperatures begin to rise again, Thomas said people should continue using caution when entering the lake, especially during periods when cold water moves toward the shoreline.
"We always advise caution when dealing with cold water, especially in the Great Lakes," Thomas said. "Cold water poses its own hazards, and it's definitely recommended that if you are going to be in the water, to use caution."
Thomas said the National Weather Service's focus during events like this is monitoring the winds and water conditions.
He added that questions about how upwelling affects coastal ecosystems, including fisheries and wildlife, are outside the agency's area of expertise.
For swimmers and beachgoers, Thomas said the main takeaway is that Lake Michigan conditions can change depending on weather patterns, and water temperatures can fluctuate significantly when winds shift.
A period of strong northerly winds can bring much colder water to shore, while a change in wind direction can allow warmer water temperatures to return.
While this week's upwelling event is already beginning to fade, it serves as a reminder that Lake Michigan is constantly changing, and that even during the warmest days of summer, the Great Lakes can still surprise those who venture into the water.
This story is brought to you as part of a partnership between WKAR and Michigan State University’s Knight Center for Environmental Journalism.