What is a bomb cyclone?

A bomb cyclone is a mid-latitude storm that undergoes bombogenesis, defined as a drop in central pressure of at least 24 millibars within 24 hours at the latitudes where most such storms occur. The term dates to a 1980 meteorology paper and describes rapid explosive deepening rather than any resemblance to a weapon. The mechanism is typically a strong temperature contrast between cold continental air and warm ocean water, combined with an energetic jet stream aloft that evacuates air from the storm's center faster than it can flow in at the surface.

The effects follow from the pressure gradient. Rapidly falling pressure produces winds that can reach hurricane force, heavy precipitation that falls as snow on the cold side and rain on the warm side, and significant coastal flooding when the storm's winds and low pressure push water onshore. The nor'easters that hit the northeastern United States are frequently bomb cyclones, and the storms that cross the northern Pacific and strike the West Coast, sometimes carrying atmospheric rivers of tropical moisture, often are too.

The term entered public use around 2018 when media coverage adopted it during a strong East Coast storm, which produced complaints that meteorologists were sensationalizing weather. The opposite is true: the term is older than the coverage and has a precise definition, and forecasters use it because rapid intensification matters for warning lead time. What people should take from hearing it is that conditions will deteriorate faster than a typical storm, which affects when to travel and when to expect power outages.