You could say things were really spinning on the Great Lakes on Sunday when at least 40 waterspouts touched down from dark skies. The swarming spouts were so widespread that it was considered a waterspout “outbreak” by the International Center for Waterspout Research (ICWR).

At least one of the spouts on Lake Erie appeared to move ashore, which would technically classify it as a tornado. Other spouts danced ominously in front of mariners, putting on shows for onlookers.

Although it’s uncommon to see so many spouts in one day, we’re actually in peak “waterspout season” over the Great Lakes, which runs from late July through the middle of October. In fact, exactly one year ago began a five-day stretch during which a total of 84 waterspouts were recorded, at least 42 of which spun up on Aug. 5.

Even more incredibly, another 88 spouts occurred between Aug. 16 and 18, including 51 on Aug. 18 alone! That still pales in comparison with the daily record for confirmed sightings of individual waterspouts over the Great Lakes, which stands at 67. That occurred on Oct. 20, 2013.

Last year, a record 232 waterspouts occurred in a one-week period spanning the end of September and early October.

Sunday’s environment proved ideal for the development of convective showers, or downpours and thunderstorms born from local updrafts of rising air, across the Great Lakes. Those storm cells didn’t disappoint. One photographer captured the moment a waterspout along the Cleveland lakefront came onshore.

At the time, the National Weather Service’s Cleveland-based weather radar also depicted the line of convective showers from which the spout developed. A radar loop from 10:33 a.m. through 11:42 a.m. shows the line strengthening as it moved onshore in Cleveland.

How waterspouts form

The American Meteorological Society’s Glossary of Meteorology defines a waterspout as “an intense columnar vortex (usually containing a funnel cloud) that occurs over a body of water and is connected to a cumuliform cloud.”

In simpler language, that means a narrow column of spinning air over a body of water, which is connected to a puffy cloud exhibiting vertical growth. There are two main categories that waterspouts fall into.

Tornadic waterspouts are associated with rotating supercell thunderstorms. They are true tornadoes over water. They derive their rotation from spinning clouds overhead and can contain extreme or destructive winds capable of producing damage if they move ashore. They have a better chance of inland survival upon making landfall. Tornadic waterspouts are relatively uncommon on the Great Lakes.

Fair-weather waterspouts, on the other hand, don’t require severe thunderstorms to develop. They’re born when small, invisible whirls near the water’s surface become entrained in the upward motion associated with developing cumulus clouds. That stretches the column of rotation, tightening it and making it stronger.

Fair-weather waterspouts occur most frequently when a relatively deep layer of colder air overrides the warmer waters of the lakes. Instability in the lower atmosphere produces updrafts that develop as buoyant warm and moist air near the lake surface rises into the colder air. That helps cumulus clouds build higher and higher into the atmosphere.

The necessary near-surface spin is maximized along local land breezes, where air converges and forms a spattering of small eddies. Any dominant whirls can be stretched through the updrafts into the parent clouds, eventually developing into a waterspout.

Waterspouts often occur in tandem with convectively generated rain showers, and they generally have weak circulations/winds. However, the bigger ones can produce wind gusts exceeding 50 mph and have the potential to capsize small boats or damage docks if they come onshore.

Fortunately, these types of waterspouts also move relatively slowly and are most often visible from great distances over the flat expanse of the lake, so there is ample time to get out of their way. With today’s access to cellphones, it also allows for some spectacular photos and videos!

Waterspout season on the Great Lakes

Great Lakes waterspouts occur when warm waters are met by cool air aloft. Summertime water temperature on Lake Erie can occasionally warm to 80 degrees.

The first signs of autumn manifest by early August, meanwhile, when breaths of cooler air from Canada first intrude across the U.S. border and over the Great Lakes.

This combination leads to perfect waterspout-producing conditions and demarcates a waterspout “season.” It is a subset of the same lake-effect season that produces epic snowstorms in the late fall and winter on the Great Lakes.

Based on the past few days of waterspout reports, it should come as no surprise that August and September are the most common months for waterspouts.

Where else do waterspouts occur?

Fair-weather waterspouts, also sometimes referred to as “cold-air funnels,” are common in other parts of the world, at roughly the same latitude, where weather is similar.

Bodies of water such as the Mediterranean, Baltic, Adriatic and Aegean seas are breeding grounds for spouts. Researchers studying those locations note that they produce the most spouts in August and September.

With a disclaimer that nobody should venture too close to these spectacular occurrences of Mother Nature, if you live along the shores of the Great Lakes, keep the cameras handy. Stay tuned throughout the latter part of this summer and into the fall for what promises to be another one of the many “seasons” that occur on the Great Lakes.

Tom Niziol recently retired as winter weather expert at the Weather Channel after a 32-year career at the National Weather Service office in Buffalo.

Matthew Cappucci contributed to this report.