Few things in creation are as terrifying as a tornado. A list of weather statistics can never conjure the humid yellow sky and the heavy feeling that something is coming.
My mother and I were in a car when we saw the thunderclouds, and she gave a little cry when the huge funnel cloud slowly snaked out of the sky. We raced down the road while I cowered, watching the storm relentlessly bear down on us.
Within minutes we were safely in a storm cellar, yet the memory of that huge gray swirl of winds, roaring and chasing us down the road still lingers.
Source: NOAA 
When we read the reports of last week's tornadoes, I always visualize it through the eyes of my childhood memory. Tornadoes are the monsters of the weather world.
This past week, they rampaged through 14 states and killed 39 Americans.
As a weather woman, I can tell you why this outbreak happened. We are at the tail end of a strong La Niña, making the jet stream volatile. This allowed cold air to plunge deep into the South, where it crashed into the warm moist air from the Gulf of Mexico. The Gulf is warmer than it usually is, this time of year, so the atmosphere was unusually moist. The result was explosive, generating deadly tornadoes from Oklahoma through North Carolina.
The Gulf will continue to grow warmer. The La Niña and its impact on the jet stream will linger for another month. And May, not April, is the busiest month for tornadoes.
Times of year when tornadoes are more common – shown as tornadoes per million square miles per state. Source: NOAA 
As a professional, I can dryly state that we can expect hundreds more tornadoes this year. As a former child, I can warn you that they can be monsters. If you live in “Tornado Alley”– be careful out there.
Evelyn Browning Garriss, historical climatologist, is a longtime writer for The Old Farmer's Almanac. She is also editor of The Browning World Climate Bulletin  and has advised farmers, businesses, and investors worldwide on upcoming climate events and their economic and social impact for the past 21 years.