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Clouds That Spell Severe Weather on the Horizon

March 4, 2020
By Anesa McGregor , Emmetsburg News

With warmer weather in our future, I thought it would be a good idea to look at some signs bad weather is approaching.

As any trained storm spotter can tell you, when severe weather threatens, look to the sky. Clouds are often the first sign that skies are turning unfriendly. Look for the following types of clouds during unsettled weather; recognizing them and the severe weather they're associated with could give you a head start to find shelter to protect yourself.

Cumulonimbus clouds are thunderstorm clouds. They develop when heat and moisture move upward into the atmosphere. The convective air currents that create these clouds are so powerful, their air rises tens of thousands of feet, condensing rapidly. The result is a cloud tower with bulging upper portions.

If you see a cumulonimbus, you can be sure there is a nearby threat of severe weather, including hail, burst of rainfall, and possibly even tornadoes.

Anvil clouds are not stand-alone clouds. They are a feature that forms at the top of a cumulonimbus clouds. This anvil top of a cumulonimbus cloud is actually caused by the cloud hitting the top of the stratosphere (the second layer of the atmosphere). The stratosphere acts as a "cap" to convection with the cooler temperature at the top of the layer discouraging thunderstorms. The top of a cumulonimbus cloud has nowhere to go but outward. Strong winds fan this cloud moisture out over great distances, which is why anvil clouds can extend for hundreds of miles from the parent storm cloud.

Wall clouds form under the rain-free base (bottom) of cumulonimbus clouds. It takes its name from the fact that it resembles a dark gray wall (sometimes rotating) that lowers down from the base of the parent storm cloud, usually just before a tornado is about to form. In other words, it is the cloud from which a tornado spins. Shelf clouds also form underneath thunderstorm clouds the same as wall clouds, which does not make it easy for an untrained eye to differentiate between the two. A shelf cloud is associated with thunderstorm outflow (not inflow like wall clouds) and can be found in the storm's precipitation area (not rain-free area like walls clouds).

Funnel clouds are one of the most feared and easily recognized storm clouds. Produced when a rotating column of air condenses, funnel clouds are the visible part of tornadoes that extend downward from the parent thunderstorm cloud.

But remember, not until the funnel reaches the ground or "touches down" is it called a tornado.



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