What is a bomb cyclone, which may deposit 20 trillion gallons of rain on US?

Weather phenomenon bombogenesis, popularly called 'bomb cyclone', may deposit 20 trillion gallons of rain on western US, meteorologists have warned. Bombogenesis happens when a cold air mass collides with a warm air mass and marks a minimum 17-millibar drop in atmospheric pressure in 24 hours. It often delivers hurricane-force winds, torrential rains and snowfall in mountainous regions.