Scud Cloud
Source: WOODTV
SCUD stands for Stratocumulus Under Downdraft. That's exactly where you will find them, under the downdraft of a shower or storm. SCUD clouds can oftentimes appear to be threatening, but they are as harmless as a cotton ball cumulus cloud. These low-hanging dark clouds often appear next to rain shafts, especially thunderstorms. Often times they appear to look like fingers reaching out from below the storm, or can even look to be a tornado.
Below is an image taken in 2000 over Grand Haven MI.
SCUD is an actual meteorological term. In fact, in the American Meteorological Society glossary, it is defined as "Ragged low clouds, usually stratus fractus or Cumulus fractus, that occur below the main cloud base." It happens when rain or more saturated air in the downdraft mixes as it falls into the dry air near the surface.
Often times scud can look so ominous, people mistake it for a tornado or a funnel cloud. Here are some key differences between tornadoes and SCUD clouds:
- Tornado funnels will never detach from the cloud base, SCUD will.
- Tornado funnels are rapidly rotating columns of air, they will never stop rotating. SCUD will sometimes stop twisting, or just float.
- Tornadoes will move with the cloud. SCUD will often move faster or in a different direction than the main cloud.
- Tornado funnels will often be very defined. SCUD twists often look fibrous or wispy.
- Tornadoes spin down from a lowering in the cloud base. SCUD can appear under any part of the downdraft.
- Tornadoes only form from strong storms. SCUD can form on any shower or storm.