Tornadoes have the notorious reputation of being one of the most unpredictable forces of nature. Even with the most advanced and sophisticated technology and equipment, it is impossible to predict where and when a tornado may form or how severe the storm may be.
Even when the conditions seem absolutely prime for a storm to develop, a tornado often doesn’t appear. At other times, there are only a few of the weather signs that point to the formation of a tornado and yet one or more may appear.
This is not the only problem with tornadoes. They also don’t seem to stick to any rules regarding the size, severity of the storm or how long they will last. In general, tornadoes last no longer than ten minutes. However, the larger the twister, the longer it will last and this could be for up to 30 minute.
Wind speeds can vary from anywhere between 110 miles per hour to 300 miles per hour (some estimates place the 1967 Oak Lawn tornado at 250 mph). The width or diameter of a twister can range from 250 feet to over 2 miles in size. There is also little to no way to predict the path that a twister will follow. All of these factors are important as they determine how much damage a tornado is likely to do.
This said, there are some common elements that can be attributed to the formation of tornadoes.
First, warm and moist air needs to be present near the surface of the ground in conjunction with colder, drier air higher up. This creates a wind shear or horizontal vortex.
Hot air rises and as the warm moist air climbs, it forces the cool, dry air down, resulting in what is referred to as an updraft. An updraft basically pushes a portion of the horizontal vortex up essentially forming two vertical vortices.
The vortex with the greater force becomes the center of the storm while the other normally dissipates. The warm updraft forms the center of the vortex while the cool downdraft is outside of the vortex, forming what is called a supercell. This supercell system and exchange of warm and cool air is what drives the formation of a mesocyclone which appears high above the ground.
A tornado, where the vortex moves down towards the surface of the earth, will only form in about 30% of supercell events.
Another factor that may contribute to the formation of tornadoes is the presence of a cumulonimbus cloud. These are the big, heavy rain clouds that we often associate with storms. However, this is not a necessary ingredient and a tornado can form without the presence of any clouds at all.
It seems that every factor and condition needs to be just about perfect for a tornado to form, or so researchers believe. The truth is, they simply don’t know why some thunderstorms result in twisters and others don’t. They also have no evidence that they can use to accurately predict the size and therefore duration of a twister or if more than one will form.
The course or path that the tornado will follow is as unpredictable. Storm chasers are common in areas where tornadoes are prolific and their main goal is to find a means to predict these destructive twisters in order to minimize the damage that they can do.
A tornado will normally dissipate when there is no more warm, moist air near the surface of the ground or cold air higher up in the atmosphere to keep driving the storm. Currently weather warnings for tornadoes only provide information on conditions that may lead to the formation of a tornado but will not always result in one.