Thunderstorms occur every year, but did you know there were different types of thunderstorms? Yes! As a matter of fact, there are 3 types of storms that impact us and our communities. The types of storms are: multicell, single cell, and supercell. Each set of storms comes with their own threats; however, some are more common to occur in specific thunderstorms. The threats include: hail, damaging wind, tornadoes and flooding.
First, we’ll begin with the most recognizable, multicell thunderstorms. These can be broken into 2 segments, a cluster and line. For now, we will touch up on multicell lines (also called squall lines). They typically occur with a cold front, however if there is a disturbance high in the atmosphere, it may also trigger storms to form into a line. The easiest way to recognize these storms is through radar, with most squall lines travelling in a west-to-east fashion. These can last for many hours at a time and travel several hundreds to even as much as 1000 miles! The most common type of severe weather that occurs with a squall line is damaging winds, which are sometimes upwards of 90 mph. Wow! That will do a number to the trees and power lines in your neighborhood. Occasionally, you also can see some hail from these, but if that is the case, it is typically quarter sized or smaller. In terms of flooding, it is rare that a multicell line results in flooding since they are usually moving quickly. Tornadoes are rare as well, and are usually quick spin ups that do not last very long. So, if there is a squall line approaching your area, it would be a safe assumption that damaging winds will be the main threat as it passes overhead.
This is an image of a well-defined shelf cloud from a strong squall line taken by myself (meteorologist Bobby Bianco), in Kansas. Shelf clouds form from rain cooled air racing ahead of the storms and interacting with the warm/humid air.
Next, we will dive into single cell storms. These are the most common type of storm in the Midwest and Northeast since they occur frequently in the summer. These form during warm/hot and humid days with some type of weak forcing mechanism. This mechanism can be a disturbance in the upper atmosphere, lake or sea breeze, and even a cool “outflow” breeze from a dissipating storm. These storms are infamous for popping up very quickly, producing moderate to heavy rain and sometimes gusty winds during their mature phase. They can last from 30 minutes to as long as 1 – 2 hours. Their typical severe weather is gusty winds and localized flooding. Small hail around pea to penny size can occur, but tornadoes are very rare.
This picture is also in South Dakota. It is the image of a quick pop-up single cell storm. You can see the rain shaft under the cloud (darker grey area). Courtesy Bobby Bianco.
Finally, one of the most dangerous thunderstorms is the supercell (Cue Jaws Music). These are a little less common in the Northeast, but more prominent in the Midwest and Plains States (i.e. North Dakota to Texas). Supercells typically last for several hours and can trek hundreds of miles. These storms can produce every type of severe weather, from very large hail to massive, long tracked tornadoes and even damaging winds and flooding. Supercells are usually the picturesque ones that have a well-defined structure and produce the strongest tornadoes. They typically occur when it is warm/hot and humid and when there are winds at ground level coming from the south/southeast with winds thousands of feet in the air moving in a more westerly direction. Picture your right hand pointing straight ahead from your body as the surface wind and your left hand “karate chopping” on top of your right hand as the wind high above our heads. That is basically what the winds look like as you go up in the atmosphere. This motion causes turning in the atmosphere and can result in rotating storms. That turning can make its way down to the ground, resulting in a tornado. Some tornadoes can have wind speeds over 200 mph and can be over 1 mile wide! Also, supercells can produce hail over quarter sized, sometimes larger than grapefruits! Thankfully, that is extremely rare and may never happen in the Northeast, but it does happen in the center of our country. However, if large hail happens to pass over a car dealer, they will probably have something called a “hail sale”. But enough about that, these monster storms are often accompanied by wind gusts (not including tornadoes) over 60 mph and very heavy rain resulting in flash flooding.
This image of a very strong supercell is from Wyoming. This produced numerous tornadoes and had a life span of about 5 hours while traveling nearly 150 miles. Courtesy Bobby Bianco.