The tornado frequency increases in the spring as the warm and cold seasons battle it out in the U.S.
Warm, humid air surges into the South during the spring months, while colder air remains in place across the northern tier of the country. The clash of warm, humid air and cooler, drier air to the north creates instability for thunderstorms to develop.
Another key ingredient for severe thunderstorm and tornado development is a powerful jet stream, or a corridor of fast winds around the altitude where planes fly. When there are powerful winds high in the atmosphere and weaker winds at the surface, a twisting motion in the atmosphere can help to produce rotating thunderstorms capable of spawning tornadoes.
During the spring months, the jet stream is often still potent across the U.S. before it shifts too far to the north during the summer to support violent storms with tornadoes touching down.
The sun's rays are also strengthening during the spring months, promoting increased daytime heating that further reduces the instability of the atmosphere.
Thunderstorms with the risk of damaging winds, hail, isolated tornadoes and torrential downpours will begin to shift eastward over the central United States this weekend.
A pattern favoring waves of progressively cooler air will set up across much of the Midwest and Northeast during next week and could continue into early May.
Rounds of flooding and severe storms slammed the South and Plains this week, while a storm system unleashed dust storms and snow in the West.
Ahead of the monsoon season in India, temperatures will swell well above normal in parts of India and Pakistan.
The 119th Boston Marathon will take place on Monday, April 20, and runners set to take on the historic course will face cool and potentially rainy conditions.
In a high-tech world of satellites, computers, mobile devices and wearables, the weather balloon is still an important tool which helps meteorologists create more accurate forecasts, especially in the case of severe weather.
SE Virginia (1983)
4" snow at Hampton, 3" snow at Newport News (heaviest snowfalls on record so late in the season).
Colorado Rockies (1992)
Big spring snowstorm... 12" at Vail 8" at Winter Park 10" at Copper Mountain 8" at Aspen
South Dakota (1995)
Spring snows continued. 6-12" and locally 2 feet fell between Mobridge and Aberdeen. A stretch of I-90 had to be closed.