'If it doesn't spin, don't call it in' Knowing the difference between scud clouds and funnel clouds

Tornado sirens roared across towns in northern Illinois with reports of a funnel cloud spotted in Loves Park Monday evening.  At that time, a line of stronger storms were present, but there were no severe thunderstorm warnings out and radar showed no indications that any of the storms were rotating.  In fact, with the wind velocity shown on radar, it would have been quite hard to get any rotation from that line.  So, what could have possibly happened?

Everyone's severe weather awareness was likely up due to the forecast of possibly damaging wind thunderstorms for later in the day.  And when a Tornado Watch was issued during the afternoon, I image the weather awareness went up even further, which is good, but you also need to keep your severe weather spotting classes in mind.  While watches and warnings should not be taken lightly, it's also important to realize that not every thunderstorm that develops under a Tornado Watch will produce a tornado.  While I haven't seen any photos from that particular storm that had the 'supposed' funnel cloud, I can suspect that there were a lot of low hanging clouds that possibly resembled funnel clouds.  Often times these low hanging clouds, otherwise known as Scud Clouds, can be easily mistaken for funnel clouds.  After all, they look very ominous and scary, but they pose no severe weather risk.

Anyone who has been through a storm spotter training class with the National Weather Service will know this saying: 'If it doesn't spin, don't call it in'.  All thunderstorms will have updrafts and downdrafts.  Updrafts help build the storms with the warm, moist and humid air and downdrafts are the rain, hail and wind.  When you think about it, there is a lot of turbulence in the atmosphere that comes with thunderstorms that can often times lead to those scary looking clouds.

By definition, Scud Clouds are low ragged and wind-torn appearing cloud fragments, usually not attached to the thunderstorm base, often seen in association with, and behind gust fronts. Scud clouds DO NOT produce severe weather. Scud clouds are often mistaken for wall clouds and tornadoes, especially when attached to the thunderstorm base. A way to differentiate scud clouds from wall clouds is to watch their relative position with respect to the rain area: scud clouds move away from the rain area while wall clouds maintain the same relative distance.  (National Weather Service Glossary)



Sissy Ziech
Rochelle, IL

 

Most often, scud clouds are mistaken for funnel clouds with shelf clouds.  Shelf clouds form along the leading edge of a line of thunderstorms.  The image on the left is a picture of a shelf cloud from Monday in Rochelle.  Notice the jagged looking clouds on the bottom.



A funnel cloud is a rotating column of air not in contact with the ground, extending from a towering cumulus or cumulonimbus base. Funnel clouds are found at the rear of the storm, usually from a wall cloud.  (National Weather Service Glossary)

Melinda Kerwin
South of Rochelle, IL

Here's another Rochelle photo that Melinda Kerwin took Monday night.  At first glance, it would appear that there are several possible funnels hanging from that storm cloud, but at closer inspection the clouds are very jagged and were likely not moving or rotating.  It's important when spotting, or taking pictures of storm clouds, not to assume that every low hanging cloud from a thunderstorm is a funnel or tornado.  Here are a couple questions you need to ask yourself before making a determination:  Is the cloud rotating over time or is it remaining stationary?  Is there an apparent wall cloud with this storm?  Where in respect to the rain is this cloud located?  If you're still not sure, snap a picture and either send it in to the National Weather Service or the First Warn Weather Team.  You can even call and describe what you're seeing.  From that, looking at the radar as well as talking with the National Weather Service, we can determine whether or not it's a possible funnel cloud.