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Weather Bombs: Rapid Storm Development

© Keith C. Heidorn

The propensity for military-related language in the media has brought a rise in the use, and misuse, of of the term weather bomb in the last decade. The term bomb in combination with weather events appears to have first arisen during the war years of the 1940s when meteorologists began calling intense storms over the northwestern Atlantic Ocean "bombs". These "bombs" were storms with all the ferocity of hurricanes, and yet were not truly hurricanes (like 1991's Perfect Storm) that had the potential for damaging ships as great as enemy bombs.

Over the succeeding years, the term evolved into the description of a specific form of storm development characterized by MIT professor Fred Sanders in the 1980s as being an extratropical low pressure cell in which the central barometric pressure drops at least 24 millibars (2.4 kPa) in 24 hours. Sanders called such cyclones, bomb cyclones because of their explosive development.

Bomb cyclones rated headlines during the1990s when several were called the "Storm of the Century" and the "Perfect Storm" by US eastern reporters. These storms generally resulted in severe blizzards forming out of Nor'easters that struck the northeastern coastal states and Canadian provinces. Many of these storms began as Colorado Lows or Gulf of Mexico lows that underwent explosive cyclogenesis, the rapid formation of an intense winter storm over a short period when they moved off the land and into the warm Gulf Stream waters off Cape Hatteras.

As a result weather bombs, or more appropriately bomb cyclones, have been associated with the eastern North America coast and offshore waters, though they also form off the Asia coast in the Western Pacific and over the eastern Atlantic and Pacific Oceans. The Pacific Northwest Region of North America has seen some of its most devastating storms arise from bomb cyclogenesis.

The bomb cyclone know as The Perfect Storm forms off US East Coast

As I said, bomb cyclones have characteristics similar to hurricanes in their power and precipitation intensity. They may produce winds of hurricane force (greater than 74 mph / 118 km/h), and a few have developed distinct "eyes" when viewed from satellites. However, there are many major differences between the two storm types.

First, bomb cyclones form at high (non-tropical) latitudes during the cold season (late-fall, winter, and early spring), the general opposite of tropical storm formation. Bomb cyclones have cold air and fronts associated with them which hurricanes do not, and indeed, cold air is an essential ingredient for a bomb cyclone, while it kills a hurricane. And finally, bomb cyclones require strong upper-level winds to develop, whereas such winds destroy hurricanes.

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