The Great Lakes may not be known for Tornado Alley-style storms, but they still produce remarkable weather events.
Few weather events are as disruptive as the lake-effect snow bands that develop during winter.
Then in the summer months, these same lakes provide us with gentle breezes that assist in shaping our weather forecasts. As summer gives way to autumn, a different weather phenomenon begins appearing across the Great Lakes.
These narrow columns of rotating air can suddenly appear beneath ordinary-looking clouds.
Some disappear again within only a few minutes, leaving little trace that they were ever there.
Warm lake water and cooler air create the right setup
Waterspouts occur throughout the United States’ Great Lakes during the late summer months (August through September), and then again in early fall (October). They form when warm lake water is overlain by cooler air moving across the region.
National Weather Service (NWS) meteorologists use temperature differences between the cold air flowing above warmer water to predict waterspouts.
Meteorologists also evaluate moisture levels and wind speeds in the lower atmosphere.
While many people think of a waterspout as being similar to a tornado over water, meteorologists actually categorize them into two groups. Tornadic waterspouts usually start off as tornadoes associated with thunderstorms before they cross into a body of water.
Fair-weather waterspouts develop directly over bodies of open water and are generally less powerful, shorter lived, and much more numerous.
NOAA defines a waterspout as a whirling column of air and water mist.
Since fair-weather waterspouts do not normally develop into severe thunderstorms, they commonly originate from cumuliform clouds. A majority of the time, by the time a funnel cloud has developed, the waterspout will have already reached its maximum strength.
Most waterspouts are relatively short-lived
Waterspouts typically last between 2 and 20 minutes. They usually travel at speeds ranging from 10 to 15 knots over the water during their lifetime.
The National Weather Service has identified several stages in the life cycle of a waterspout.
The first stage is development, which begins as a darkened area on the water.
It often appears as a small circular patch on the surface.
As it grows larger, a spiral-shaped pattern may become visible near the center. Then, as winds strengthen within the circulation, a ring of spray begins to form.
After that, stronger winds allow the funnel cloud to extend downward and connect with the cloud base above.
This is usually when the spray vortex reaches its greatest height, often rising hundreds of feet above the water and leaving behind a noticeable wake of turbulent waves.
In the final stage, the funnel cloud weakens, breaks apart, and eventually dissipates.
While most waterspouts do not grow large enough to cause significant damage, NOAA says the tornadic variety can be extremely dangerous. When one moves onto shore and presents enough danger to the public, the National Weather Service may issue a Tornado Warning.
Why meteorologists pay close attention to them
Forecasting a waterspout involves much more than simply tracking cool air moving over a warm lake. Meteorologists examine water temperatures, air temperatures, moisture levels, and wind conditions when assessing waterspout potential.
When waterspout conditions become favorable, the NWS may highlight the threat in marine forecasts and Hazardous Weather Outlook statements.
Once they are detected by radar or reported by observers, Special Marine Warnings may be issued for affected areas.
To avoid dangers presented by waterspouts, NOAA advises boaters to remain alert, maintain a safe distance, and not approach them even though curiosity may get the best of you.
Boaters encountering a waterspout should move away from its expected trajectory and find safe harbor if feasible.
Read the whole thing?
Get the week's signal, not the noise
Our sharpest reporting on energy, climate and nature — free, once a week.
