We've heard a lot about a ‘bomb cyclone’ over the last couple of days, but what is it?
The term has been around for decades and was actually created by a graduate student and an adviser at MIT back in 1980. John Gyakum, a graduate student at the time, was helping Frederick Sanders write a paper about strong low pressure systems. They were trying to determine why some storms had such explosive development and decided they should call these explosive storms “bombs.” Eventually, the term ‘bomb cyclone’ was used to describe a storm with rapid intensification.
Most storms that cross over land do not have a rapid, intense drop in pressure. Storms with those characteristics are usually found over water. On occasion, a storm like the one we witnessed this week, will have a rapid decrease in barometric pressure and bring intense weather conditions similar to those we would usually see with a tropical storm. Strong wind, heavy precipitation and colder temperatures are common with the particular storms with the wind being the main concern. Wednesday, we certainly felt the strong wind blowing across southeastern Arizona and that wind caused blizzard conditions east of the Rockies and into the Central Plains.
To become a ‘bomb cyclone’, the central barometric pressure of the storm must drop at least 24 millibars in 24 hours. Or, since we are used to measuring barometric pressure in inches, a drop of 0.71” in 24 hours. Rapid pressure drops such as these resemble those you would find with a tropical storm or hurricane. This explains the strong wind that develops in association with the storm.
The process of a storm undergoing such rapid intensification is known as “bombogenesis.” The term comes from the merging of the words bomb and genesis. Bomb refers to the explosive development of the storm. Genesis refers to the creation of the cyclone, otherwise know as a storm. Essentially what happens is as a cyclone develops, air starts to rise rapidly and begins to spin counterclockwise. In the Southern Hemisphere, cyclones spin clockwise. When the air rises rapidly, a vacuum effect results and lowers the air pressure. Average winter storms generally have a barometric pressure just over 29.53” of mercury. Some ‘bomb cyclones’ will have a barometric pressure below 29.00” which is most common with storms of a tropical origin.
‘Bomb Cyclones’ are not too common and it’s a good thing. ‘Bomb Cyclones’ can cause wind damage over a widespread area and can last for several days causing more destruction along the way. The storms usually come with heavy precipitation which can bring ground and air transportation to halt in the case of blizzard conditions. Severe thunderstorms are commonly found on the leading edge of a ‘bomb cyclone’ and have been know to cause catastrophic tornado outbreaks. ‘Bomb Cyclones’ are not storms to take lightly. Fortunately, we don’t see them too often!