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Dear Tom,
Can you explain what a bomb cyclone is?
—Jack W. Hardekopf Aurora
Dear Jack,
A “bomb” cyclone is a term applied to a rapidly intensi- fying low-pressure system in which the central pressure drops at the rate of at least one millibar an hour for 24 hours. In terms of inches of mercury, that’s pressure falling at least .03 inches an hour for 24 hours. This rapid intensification often occurs with cold-season storm systems off the Atlantic Seaboard referred to as nor’easters, which produce many of the region’s major snowstorms. While not as common, these storms also occur in the Midwest. On Dec. 14-15, 1987, low pressure moving northeast “bombed out,” bringing 8-12 inches of heavy, wet thundersnow to the Chicago area. Last weekend, a bomb cyclone brought 50 mph winds and seven inches of rain to portions of northern California.