Ask Ellen: What are SCUD clouds?

GRAND RAPIDS, Mich. (WOOD) — We are entering into storm season here in West Michigan which means a lot of fantastic looking thunderstorms are likely to sweep our area. Inevitably, some have some very ominous looking features, some of which are SCUD clouds.

This picture has gotten quite a bit of traffic on Facebook of some low-hanging SCUD.

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.

SCUD stands for Stratocumulus Under Downdraft. That’s exactly where you will find them, under the downdraft of a shower or storm.

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 because these clouds are hanging beneath a cloud base, it can make them look like they are a funnel cloud to some observers. You can see the scud clouds here in this image below Most of the SCUD here is detached from the cloud base, and floating below. Often these will move faster than the main cloud deck too.

Some SCUD can look very funnel-like as they twist below the cloud deck. This is a key example below:


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:

  • 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.