Historic 'bomb cyclone' freezes North America

A bomb cyclone, or bombogenesis, is a quickly intensifying storm that occurs when air pressure drops 20 millibars or more within 24 hours.

The extreme cold weather hitting North America in the run-up to Christmas holidays is due to a phenomenon called a "bomb cyclone".

The U.S. National Weather Service said this "once in a generation type event" has the power to turn deadly and is already breaking cold-weather records — with temperatures falling to minus 53 degrees Celsius (minus 63 Fahrenheit) in western Canada, minus 38 in Minnesota and minus 13 in Dallas.

It's even snowing in subtropical northern Florida.

A bomb cyclone, or bombogenesis, is a quickly intensifying storm that occurs when air pressure drops 20 millibars or more within 24 hours.

This usually happens when a warm air mass collides with a cold one, according to the National Oceanic and Atmospheric Administration.

This time air from the Arctic ploughed into tropical air from the Gulf of Mexico, forming a depression bringing rain and snow.

What makes this storm extraordinary is just how fast the pressure dropped -- 40 millibars in 24 hours, according to meteorologist Yann Amice of analysts Weather'n'co.