SIOUX CITY, Iowa (KCAU) — Spring is here and severe weather season is upon us once again. Here in Siouxland, that could mean anything from damaging winds and large hail to tornado outbreaks. Oftentimes we get those classic pop up thunderstorms, gone seemingly as quickly as they developed. However, did you know there are a variety of thunderstorm modes, each with their own unique characteristics.

Some of the most common types of storms and storm systems we tend to see here in Siouxland include: single/multi-cell; squall lines: supercells; and MCSs. Another rarer type of storm system is a derecho, which we’ve seen a few of over the past couple of years or so. I’ll break these types down a bit more.

A.) Single/Multi-Cell Thunderstorms

Single cell thunderstorms are exactly what they sound like, an individual storm. These are typically short-lived and weak and are usually driven by the peak heating of the day. They usually end up raining themselves out after an hour or so, sometimes creating an outflow boundary of cooler air which helps new storms develop. As new storms develop along the outflow boundary, you get multi-cell storms, with multiple storms in various stages of growth and decay. Multi-cell storms can last for hours and are capable of producing hail, strong winds, brief tornadoes, and flooding. However, these storm often remain below severe limits.

B.) Squall Lines:

Squall lines are fast-moving lines of storms, oftentimes severe, that produce high winds and heavy rain. These lines tend to be longer than they are wide, frequently hundreds of miles long but only 20 miles wide or less. While they do sometimes produce tornadoes, squall lines are less likely to be tornadic, with damaging winds the major threat with this mode of storms. Sometimes parts of the squall line or the entire squall line become arched or bowed out in what we call a “bow echo.” Bowed sections of a squall line can produce areas of enhanced damaging winds and sometimes even briefly spin up tornadoes. However, not all squall lines have embedded bow echoes.

C.) Derechos:

This brings us to derechos. Derechos are long-lived bow echoes. By definition, a bow echo that persists with widespread wind gusts 58 mph and leaves a damage swath extending 240 miles or more, it is classified as a derecho. These typically don’t produce tornadoes, however, they leave behind a large swath of straight-line wind damage comparable to tornado damage. Some notable recent derecho events include the August 10, 2020 derecho that left a long trail of destruction through parts of Iowa, and a bit closer to Siouxland, the May 12, 2022 derecho which impacted much of the area with 50-100 mph winds and the July 5, 2022 derecho which produced widespread winds 60-100 mph. These storms are typically relatively rare, tending to only happen between once a year in a few areas to once every two to four years in many other severe prone regions of the US.

D.) Supercells:

Another type of storm we see, although far less common than squall lines, are supercells. These are actually the least common type of storm. However, when we see them, supercells are highly likely to produce severe weather, ranging from destructive winds, very large hail, and weak tornadoes, to violent, long-lived, long-track tornadoes. In fact, some of the worst tornadoes in US history have been born from supercells, including the May 22, 2011 Joplin, MO tornado, which was the costliest tornado on record, the April 1974 and April 2011 Super Outbreaks, which were the two largest outbreaks in US history, and the May 31, 2013 El Reno, OK tornado which went down in history as the widest tornado on record at 2.6 miles wide. Supercell thunderstorms were also responsible for the June 16, 2014 outbreak which included the Pilger, NE twin tornadoes. What makes supercells so unique is that they have a mesocyclone, which is a deep, persistent rotating updraft that can keep supercells alive for several hours.

E.) Mesoscale Convective System (MCS):

One other type of storm system we may see here in Siouxland is a MCS or Mesoscale Convective System. These are essentially large clusters of storms that as a whole act as a storm system. An MCS can oftentimes be spread across an entire state and persist for more than 12 hours. These could look like clusters or a solid or broken line of storms and can produce severe weather. MCSs are common in the late spring and summer months and oftentimes occur at night, typically producing flooding rains, damaging winds, prolific lightning, and sometimes hail and tornadoes. The most common type of MCS in our area is a MCC or Mesoscale Convective Complex which is easily identifiable on infrared satellite as a large, round cluster of showers and storms occurring during the overnight and early morning hours. These also usually happen in late spring and into the summer. Bow echoes are also considered mesoscale convective systems.