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.
Rounds of showers and thunderstorms will move through the Pittsburgh area this weekend with the threat of severe weather.
Stifling heat will persist across the Plains and Deep South this weekend before focusing on the West during the upcoming week.
A 10-month-old girl, who was in foster care, died after being left in a hot car in Wichita, Kansas, Thursday night, according to The Associated Press, as high heat gripped the area.
More summer-like conditions will return to the Boston area for a brief time before a front pushes through the region during the latter part of the weekend.
More summer-like conditions will return to the Washington, D.C., area for a brief time before a front pushes through the region during the latter part of the weekend.
More summer-like conditions will return to the Philadelphia area for a brief time before a front pushes through the region during the latter part of the weekend.
Pueblo, CO (1993)
A double record: 52 degrees in the morning and 101 degrees in the afternoon.
Chester County, PA (1994)
1.5" of rain in 30 minutes.
Wildwood, NJ (2000)
More than 4" of rain.