May 22, 2013
Big Story Weather Special: Tornado Safety
Here is some information that you can use to help yourself prepare for tornadoes.
First, tornadoes only form when conditions are right. What that means is you need to have three ingredients to come together. These ingredients include warm moist air from the Gulf of Mexico, dry air from the middle levels of the atmosphere and cold air from the upper levels.
Here is a picto-gram of those conditions:
Now, as you look at this image, you see green arrows. This is the warm moist air that is rising into the atmosphere. The brown arrow represents the dry and strong wind that is being pushed into the storm at the mid-levels, while the blue arrow shows the cold air sinking towards the surface. When these air masses collide together we get a spin in the atmosphere of air that wants to rise and air that wants to sink. This leads to the formation, or starting process, of a tornado.
Secondly tornadoes are most commonly associated with “Super-cell thunderstorms”. However, tornadoes can also form along the cold frontal boundary, as well. Here is what happens and where to identify places that super-cell thunderstorms could form:
About 50-150 miles ahead of the cold front, right ahead of the dashed line, is where the super-cell formation is the most likely to occur, this region is where we need to watch closely for most of these types of storms. The reason they form here is because super-cell’s like to be independent storm cells, as when they are back along the cold front the blue lined area. They may start out as super-cells, but will quickly turn into Meso-scale convective system, which means they start to group together and lose the individual characteristics which are important for super-cells.
Here is what these type of storms look like on a satellite image:
If you look at the image courtesy of NOAA, you can see both of these features present. The super-cell thunderstorm is the circular one over Northern Texas, while the ones over eastern Oklahoma and Arkansas have become the MCS (Meso-scale Convective System). The super-cell over northern Texas is a prime example of what happens to a super-cell before it merges along the cold front; it forms on the southern boundary and merges northward into the rest of the cells.
Now, if we look at radar, how can we determine the worst part of the storm, or the part that will possibly lead to a tornado? For this, the rule of thumb is that tornadoes most often form on the southeast side of the storm. So, if the storm is moving northeast, you will find the storm in the right rear section or in the southeast part for this example.
So, looking at the radar image courtesy of the National Weather Service, we can see that the storm near Wichita Falls, Texas has a yellow box around it because it is already a severe thunderstorm. However, if we look at its movement, it is moving northeast, so we would want to monitor the part that is just above the word “Falls.” This would be the part of the storm capable of producing the tornado, if there was going to be one.
Featured Image Credit: Thinkstock.com