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.
Hurricane Ignacio may enhance showers and stir rough surf for the Hawaiian Islands as it approaches next week.
After Erika brings heavy rain and locally gusty winds from Hispaniola eastern Cuba into Friday night, the system will move toward the Bahamas, the Keys and South Florida this weekend.
As many as seven tropical cyclones were churning throughout the world this past week, while smoke from wildfires across the Pacific Northwest led to poor air quality across the region.
Heat and humidity will return to Harrisburg this weekend and hang on into next week.
Heat will linger in Eastern Europe for much of the fall season; meanwhile, the British Isles and northwestern Europe can expect a stormy end to the season.
As Hurricane Katrina barreled towards the Gulf Coast, peaking at Category 5 strength while feasting on the warm waters of the Gulf of Mexico, meteorologists around the country prepared to deliver one of the most crucial and life-saving forecasts in history.
New England (1816)
"Year in which there was no summer", otherwise known to weather historians as "1800 and frozen to death" killing frost once again damages sparse corn corp in northern New England...loss of this and other crops led to severe famine in much of New England that winter...and helped spur western migration in spring of 1817.
New England (1965)
A total of 2.5 inches of snow on top of Mt. Washington set an August record. Vermont had a reading of only 25 degrees, while Nantucket had a chilly 39 degrees. Earliest freeze on record at many stations.
Houston, TX (1980)
2.23 inches of rain fell in less than 1 hour. Streets were flooded in the downtown district and a tornado touched down briefly west of Houston at Sealy, TX.