What Exactly Is a 'Bomb Cyclone' Anyway?
Much of the US east coast is being blanketed by a uniquely strong blizzard that's cancelling thousands of flights, wreaking havoc on car travel and clearing out the skies of nearly all air traffic. Everyone keeps referring to this storm using the catchy "bomb cyclone" term. So, for those wondering, let's explore exactly what a "bomb cyclone" is.
"Bomb cyclone" is a meteorological term that's the combination of two meteorological terms. So, let's break it down:
Cyclone: Simply speaking, a cyclone is just a big spinning storm with a low-pressure center. A hurricane (or typhoon if it's in the South Pacific or Indian Ocean) is perhaps the most recognizable cyclone. But, unlike a hurricane, a generic cyclone doesn't have to be in tropical/subtropical waters and have a "closed, low-level circulation."
Bomb: This is the word that catches everyone's attention — in particular the TSA agent near you when you complain about your flight cancellation. This term refers to a storm that undergoes a rapid intensification reflected as a drop in pressure of 24 millibars in 24 hours. The lower the pressure, the stronger the storm.
For reference, standard sea-level pressure is 1,013 millibars. 2017's Tropical Storm Emily made landfall in Florida at 1,005 millibars, just 8 millibars below the average. On the extreme end of the spectrum, Hurricane Maria was the 10th most intense hurricane ever with 908 millibars. All of that to say: a drop of 24 millibars is quite substantial.
The United Kingdom's Met Office — equivalent of the National Weather Service in the US — has perhaps the best 90-second explanation and illustration of a weather bomb:
So, does the storm blanketing the Northeast qualify as a bomb cyclone? Turns out that it's practically the definition of one. Remember that the pressure only needs to drop 24 millibars in 24 hours. How did it do?
That's right; this overachieving storm more than doubled its goal. Dropping 59 millibars in 24 hours, the storm currently measured at 951 millibars, leaving the storm just 11 millibars higher than Superstorm Sandy was measured at landfall.
Thankfully though, this bomb cyclone is expected to stay off of the coast. And that's good as the storm effectively a "winter hurricane" — bringing strong winds and tall waves, but heavy snow instead of rain.