Not only did Monday's storm produce much-needed rain with the sound of thunder and scattered hail, but according to the National Weather Service, it may have produced a few waterspouts along the Central Coast.

This leads to the question: What's the difference between a tornado and a waterspout?

To start, they are both columns of rotating air. The main difference is in where they form. A tornado begins over land, while a tornadic waterspout develops over water or moves from the land to the water; however, there are other types of waterspouts.

Let's start with tornadic waterspouts, which are created from a severe thunderstorm over the water like tornadoes can form over land. This type of tornado, or waterspout, starts as a funnel cloud that rotates columns of condensed water droplets. If it wasn't for the liquid water, you wouldn't be able to see it. As soon as a waterspout hits the ground, it is classified as a tornado. Debris or dirt embedded in a funnel cloud indicates that it has already touched the ground.

So what causes a funnel cloud? We understand the necessary conditions for development, but we don't precisely know if a particular low-pressure system, front or trough will produce one.

First, you need an unstable atmosphere with warm and/or humid air at the surface and cold air aloft. From earlier columns, moist and warm air is less dense, and it naturally rises.

As the air rises into the sky, it cools to the point that water vapor condenses to form visible clouds and releases tremendous amounts of latent heat. This condition keeps the air rising inside the cloud producing updrafts that can reach over 100 mph and can trigger thunderstorms. Clouds with vertical development are cumulus and cumulonimbus. "Nimbus" denotes precipitation, such as rain, hail or snow. The top of these clouds, on rare occurrences, can burst into the stratosphere at about 33,000 feet.

These updrafts can cause wind shear, the other ingredient needed for funnel clouds. Wind shear is when the air travels in a different direction and speed at dissimilar heights. The condition can cause a cylinder of air to rotate on a horizontal plane in the atmosphere but eventually turn more vertical, allowing it to reach the ground.

Even though most tornadoes occur east of the Rocky Mountains, California is not immune from these violently rotating columns of air. There have been 465 confirmed tornadoes from 1950 through 2021 in the state. In fact, on Jan. 6, 2016, an upper-level low-pressure system produced thunderstorms throughout Central and Southern California when a weak tornado touched down north of Hollister, becoming the first confirmed tornado in the United States that year.

Most of the state's tornadoes occur south of Point Conception or in the San Joaquin and Sacramento valleys. Nearly all were rated weak on the Fujita scale. The California county with the highest number of confirmed tornadoes is Los Angeles, followed by Orange. San Bernardino is the largest county in the United States by area, followed by San Diego. As you head north along the California coast, the rate of tornado occurrences diminishes.

Another type of waterspout is called a fair weather waterspout. Fair weather waterspouts are generally not associated with thunderstorms. They begin to develop on the water's surface and move upward, unlike tornadic waterspouts that start as a funnel cloud and make their way downward to the water's surface.

According to the National Weather Service, "Fair weather waterspouts form in light wind conditions, so they normally move little. If a tornadic waterspout moves onshore, the NWS issues a tornado warning as some of them can cause significant damage and injuries to people. Typically, fair weather waterspouts dissipate rapidly when they make landfall and rarely penetrate far inland."

Fair weather waterspouts are a bit similar to dust devils.

Calm to light winds are essential ingredients in their development. As the sun rises, it begins to heat the ground, and the air immediately above it becomes warmer. As the air warms, it becomes less dense and begins to rise like a hot air balloon. When the updrafts of warmer air move toward the sky, the cooler air around them rush in to fill the void. That rush of cooler air can cause a spin and form a vortex. As the warmer air continues to rush upward, it often elongates and narrows the dust devil. That causes it to spin faster, like the increased spinning of ice skaters as they bring their arms toward their bodies. The faster-moving air in the center of the dust devil produces lower air pressure and causes even more air to be drawn in.

Dust devils most often develop when you have uneven heating of the Earth's surface, such as at the interface between pavement and dirt roads or irrigated fields and dry land. Those energetic swirls that look like small tornadoes can reach more than 3,000 feet in height, with winds of more than 60 mph, and can last an hour or more.

Typically, they are short-lived and don't extend much more than 100 feet into the air, with winds around 25 mph.

As a child, I would chase these vortexes of spinning dust with the hope of becoming airborne, like the "Wizard of Oz" scene as Dorothy's home is lifted by a tornado and transported to Munchkin Country.

John Lindsey is Pacific Gas and Electric Co.’s Diablo Canyon Power Plant marine meteorologist and a media relations representative. Email him at or follow him on Twitter @PGE_John.


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