|Tornadoes can strike at any time of day, but are most common in the late afternoon or evening [AFP]
A warning of severe weather has been issued for parts of the USA.
The warning for the "high-end, life threatening event" came from the Storm Prediction Centre.
The advanced warning is partly due to the recent improvements in forecasting storms, but also due to the setup of the weather.
"We're quite sure tomorrow will be a very busy and dangerous day in terms of large tornadoes in parts of the central and southern plains,'' Chris Vaccaro, a spokesman for the National Weather Service, said on Friday. "The ingredients are coming together.''
The weather system predicted to cause the tornado outbreak has already started to show its potential. The weather service confirmed a tornado touched down about 4pm Friday in Oklahoma.
Ironically, the storm passed close to the National Severe Storms Laboratory in Norman.
Tornadoes are just one hazard from severe thunderstorms. The others include hail, strong gusty winds and lightning.
The central region of the US is particularly prone to severe thunderstorms due to the interaction between the cold dry air from Canada and the warm moist air that feeds up from the Gulf of Mexico. The difference in these two different types of air is so great that the results can be explosive.
The majority of tornadoes occur late on during the day, between 4pm and 9pm, after the sun has injected plenty of energy into the atmosphere.
On Saturday afternoon, the worst of the weather is expected in Oklahoma and Kansas, but other areas also could see severe storms.
The severe weather is expected to continue into Sunday as well, although the number of tornadoes is expected to diminish.