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.
This weekend will be one of the busiest travel weekends across the country as millions people head home from Christmas travels.
Just in time for Boxing Day and the weekend, a winter storm is set to dive into the United Kingdom and central Europe with rain and disruptive snow.
A system tracking over the Rocky Mountains will spread snow over the region and into the Plains through the remainder of the week.
While lacking across a large part of the United States on Christmas Day, arctic air is set to make a comeback during the final days of 2014.
On Christmas Day in 1776, George Washington led his troops across the Delaware River, in spite of treacherous weather, for a pivotal moment in the Revolutionary War.
Cap May, NJ (1909)
28.57" barometer reading during large coastal storm.
Record Christmas cold wave: 1 degree - Philadelphia, PA (tied record) -12 degrees - Pittsburgh, PA -12 degrees - Cincinnati, OH -4 degrees - Nashville, TN 41 degrees - Miami, FL
International Falls, MN (1991)
38 degrees - the "warmest" Christmas on record.