(Reuters) – After a string of powerful tornados struck the U.S. Midwest https://www.reuters.com/markets/commodities/devastated-kentucky-tornado-survivors-pick-through-debris-shelter-with-relatives-2021-12-12 and killed more than 100 people this weekend, attention has turned to the warning systems in place and why the movements of the fast-moving storms are so difficult to predict.

According to National Oceanic and Atmospheric Administration (NOAA), a tornado refers to a small, rapidly rotating, narrow column of air which extends from thunderstorms to ground. The United States experiences approximately 1200 tornadoes each year.

Unlike hurricanes https://www.noaa.gov/explainers/hurricane-forecasting which can be seen gathering strength days in advance, a tornado watch https://www.nssl.noaa.gov/education/svrwx101/tornadoes/forecasting lasts for four to six hours over a certain area when favorable conditions develop for tornadoes.

Most hurricanes have a diameter of hundreds of miles. They can also last days to weeks. Scientists are able to predict the path of a hurricane three to five days ahead. A tornado usually forms in just a few moments, is normally only about a hundred feet across, and can last for several minutes.

Tornado watches https://www.nssl.noaa.gov/education/svrwx101/tornadoes, which are not the same as tornado warnings, are typically issued hours in advance by meteorologists watching the weather 24/7 across the United States and cover parts of a state or several states. Although they indicate the possibility of a tornado, they are not guaranteed to be a result.

Meteorologists in local offices of the National Weather Service issue a tornado warning when a tornado is either reported by spotters or indicated by radar https://www.weather.gov/safety/tornado-ww and there is a serious threat to lives and properties in its path. The average lead time for tornado warnings is eight to 18 minutes https://weather.com/storms/tornado/news/2021-04-05-tornado-warning-nws-accuracy, according to Weather.com.

Many towns use public warning sirens https://www.weather.gov/unr/Warning_Systems to warn of tornadoes, but rural areas and smaller towns do not have them. Many local television and radio stations broadcast warnings. There are also many apps for smart phones and wireless emergency alerts from FEMA. These alerts come directly from mobile towers within the area of flash flooding and tornadoes.

Overnight thunderstorms and a supercell storm in northeast Arkansas were the catalyst for the tornado outbreak that occurred over the weekend. The storm moved through Arkansas, Missouri, Tennessee and Kentucky.

Because the tornadoes struck at night, this time was even more tragic.

To go to shelter, people rely on visual confirmation. Jeff Masters is a Yale Climate Connections meteorologist.

Masters said that the massive size of the largest cell, which measures a mile in width, was another reason for widespread destruction. This means that there is no safe place. The threat is so great and powerful, even shelter can not protect you from it.