PENNSYLVANIA, USA — Is that a scud cloud or a funnel cloud I'm seeing? Stormtracker 16's Joe Snedeker explains the difference.
Have you ever felt chilly when coming out of the shower or bath? We all have! When water lays on your skin after a shower, it eventually evaporates into the air, thereby using the heat from your body in the process, which then results in giving you “the chills." Evaporation is a cooling process, which also explains why sweating on a warm summer day can help cool your body!
Now consider this similar situation. When raindrops fall through the lower atmosphere from a cloud in a thunderstorm or rain shower, they will often evaporate on their way down through the sky. This evaporating water uses some of the heat in the air around it, which again results in cooling or temperature drop in the air, called evaporative cooling. Evaporation is a cooling process! If some of that “chilled air” below the cloud causes water vapor in the air to condense out and form a low cloud or fog, it will appear to “hang down” from the cloud. Rain-cooled air hanging down from the cloud base will often create the same appearance as a funnel cloud or even a tornado! Visually, it may appear as a tornado, but without the fury and destructive winds involved. Remember, this hanging-down cloud feature is saturated, rain-cooled air, just like your body was cooled coming out of the shower. The name for this ragged fog or thin, harmless curtain of saturated, cloudy air that may hang down from a cloud is called scud. Yes, SCUD!
Scud can be differentiated visually from a tornado in many ways if you notice some factors. Scud does not rotate but rather gets dragged along in slow motion from the cloud base. Scud will never have a debris field around its base like the fury of a tornado would. Also, scud often has a more diffused edge or boundary and is often accompanied by numerous other similar scud bodies.
Looks can be deceiving, so know the facts, notice the pattern of the sky around you during rain and severe weather events, and always remember evaporation is a cooling process!
Scud in the sky and that chilled feeling you get when coming out of your shower are all connected to water vapor and its changing form in response to being heated and cooled.
Tornadoes, they’re a whole different beast!