What is ‘bomb cyclone’?

• Millions of people hunkered down against a deep freeze on December 25 morning to ride out the winter storm that has killed at least 24 people across the United States and is expected to claim more lives after trapping some residents inside houses with heaping snow drifts and knocking out power to several hundred thousand homes and businesses.

• The scope of the storm has been nearly unprecedented, stretching from the Great Lakes near Canada to the Rio Grande along the border with Mexico.

• Forecasters said a ‘bomb cyclone’ had developed near the Great Lakes, stirring up blizzard conditions, including heavy winds and snow.

• The US National Weather Service said this “once in a generation type event” has the power to turn deadly and is already breaking cold-weather records.

What is ‘bomb cyclone’?

• Bombogenesis, a popular term used by meteorologists, occurs when a midlatitude cyclone rapidly intensifies, dropping at least 24 millibars over 24 hours. A millibar measures atmospheric pressure. This can happen when a cold air mass collides with a warm air mass, such as air over warm ocean waters. 

• The formation of this rapidly strengthening weather system is a process called bombogenesis, which creates what is known as a ‘bomb cyclone’.

• The term bombogenesis is a meteorological one that specifically deals with the measurement of atmospheric pressure.

• It’s called a ‘bomb cyclone’ because a low pressure (or cyclone) undergoes ‘bombogenesis’, which refers to the quick rate at which the low pressure develops.

• Bomb cyclones form when a low-pressure system moves over a region with very cold air. As the cold air moves over the system, it causes the air pressure to drop rapidly. This rapid pressure drop can lead to strong winds, as the air rushes in to fill the low-pressure area.

• Bomb cyclones can also bring heavy precipitation.

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