Twisting Our Way Into Spring
Spring is coming just around the corner, and living in the US, we know what spring brings with it – "tornado season!" As we await this transition from cooler temperatures to warmer weather that provides the optimal unstable air conditions for tornadic activity, this is a great time to gear up for teaching the science behind tornadoes. Tornadoes happen at all times of the year, but they peak during "tornado season" usually beginning in March and lasting until June. Areas in the Southern Plains (Kansas, Oklahoma, and Texas) see more tornadoes from May to early June. On the Gulf Coast, tornadoes are most common during early spring. Northern states and areas of the upper Midwest (Iowa, Minnesota, Nebraska, and North/South Dakota) have peak tornado season in June or July.
Tornadoes can be very dangerous, so it is important to know all we can about them. What is a tornado? What is the difference in a Tornado Watch and a Tornado Warning? How is tornado strength rated?
First of all, most tornadoes form during a supercell thunderstorm that has a particular combination of winds. This combination includes air rising in thunderstorms while other winds are blowing in other directions. Winds moving in different speeds and directions at different altitudes cause the rising air to start spinning, although not all spinning air creates tornadoes. For a tornado to form from all this, there also needs to be spinning air near the ground. As the spinning air near the ground speeds up and is drawn inward toward its axis of rotation, the air moves horizontally across the land and can be tilted vertically by the force of the rising, rotating air which allows a tornado to form.
Tornadoes can cause a great deal of damage and destruction, so knowing that you are in the path of one can be life saving. Because they are caused by wind and wind is invisible, we can not see one coming until a funnel is formed and by then, it may be too late to get out of the way. Thankfully, there are meteorologists who watch the weather 24 hours a day, seven days a week for weather conditions that are favorable for tornadoes and severe weather across the entire US. These meteorologists can issue a Tornado WATCH that can cover parts of a state or several states. When a Tornado WATCH is issued, we should watch and prepare for severe weather and stay tuned to a weather radio or our local weather stations. Meterorologists who watch the weather 24/7 over a designated area may issue a Tornado WARNING when a tornado has been reported by spotters or indicated by radar and there is a serious threat to life and property to those in the path of the tornado. A Tornado WARNING indicates that you should ACT NOW to find safe shelter! A warning can cover parts of the counties or several counties in the path of danger.
A tornado can leave lots of damage in its path. Looking at the damage caused, experts can estimate the wind speeds and rate the tornado using the "Enhanced Fujita Scale" (EF-Scale) that was implemented by the National Weather Service in 2007 for rating tornadoes in a more consistent and accurate matter. The EF-Scale takes into account more variables than the original Fujita Scale (F-Scale) when assigning a wind speed rating to a tornado, incorporating 28 damage indicators such as building type, structures and trees. For each damage indicator, there are 8 degrees of damage ranging from the beginning of visible damage to complete destruction of the damage indicator. Based on their results, a tornado's strength is determined and categorized. For instance, an EF-5 Tornado means it was rated the highest possible ratings on the EF-Scale and left much damage and destruction in its path. To see the EF-Scale used to rate the strength of tornadoes, click here.
For very detailed questions and answers about tornadoes, visit this FAQ page where the NOAA has compiled information from questions asked of the SPC, as well as basic tornado research information and countless scientific resources.