What is the significance of 24 millibars in 24 hours? While “millibars” may sound like the latest candy bar, this is no eating contest. When an area of low pressure strengthens, and the pressure drops 24 millibars or greater within a 24 hour period, this is known as bombogenesis. As ominous as this sounds, there is a scientific explanation for this atmospheric process.

To comprehend the specifics of bombogenesis, it’s important to first understand cyclogenesis. Cyclogenesis describes the development or strengthening of a low pressure system. In a nut shell, cyclogenesis is initiated when two air masses meet, creating a front. Because of the density differences between warm and cold air, the warm air will want to rise above the denser, cold air. It’s also important to realize that this is happening on a large-scale, so we must account for the Coriolis force, which is the main component for initiating rotation of the air masses. For low pressure systems in the Northern Hemisphere, this rotation is counterclockwise. Once cyclogenesis has occurred, the life cycle of the area of low pressure may or may not include the process of bombogenesis. It is possible for an area of low pressure to “bomb out”, or drop 24 millibars in 24 hours. The term is described as bombogenesis because of the explosive power with which the low pressure can strengthen and deepen in such a short amount of time.

Looking ahead at the forecast, it does not appear that we have any explosive areas of low pressure headed our way in the near future, however there will be some snow expected Friday night into Saturday of this coming weekend. While the totals are nothing staggering, the snow is a product of an area of low pressure that has already experienced cyclogenesis and is now propagating toward the Northeast. So no bombogenesis in the forecast this time around!