Bomb Cyclone
Also called: bombogenesis, explosive cyclogenesis
A bomb cyclone is a midlatitude storm that intensifies rapidly through a process called bombogenesis: its central pressure falls by at least 24 millibars in 24 hours, measured at 60° latitude. The threshold shrinks toward the equator, to about 17.8 millibars at the latitude of New York City.
Why It Matters
A fast pressure drop means a fast-strengthening storm, with winds and precipitation that ramp up quickly. The term describes how quickly a storm deepens, not a separate kind of storm: a nor'easter that deepens fast enough is also a bomb cyclone.
Bombogenesis can happen when a cold air mass collides with a warm one, such as air over warm ocean water. NOAA notes that 14 of the 20 hurricane-force wind events in the North Atlantic in early 2014 underwent bombogenesis.
Pressure Drop That Qualifies as Bombogenesis
| Latitude | Drop in central pressure over 24 hours |
|---|---|
| 60° | At least 24 millibars |
| New York City | About 17.8 millibars |
Frequently Asked Questions
Why is it called a bomb cyclone?
The name comes from bombogenesis, the term meteorologists use for a midlatitude cyclone that intensifies rapidly. It refers to the speed of strengthening.
Is a bomb cyclone a hurricane?
No. A hurricane is a tropical cyclone, powered by heat released over warm water. A bomb cyclone is a midlatitude storm powered by the contrast between cold and warm air masses. It can still produce hurricane-force winds.
How much does the pressure have to drop?
At least 24 millibars in 24 hours at 60° latitude. The threshold is lower closer to the equator: about 17.8 millibars at the latitude of New York City.
Related Terms
Nor'easter
A storm along the East Coast with winds blowing from the northeast. Nor'easters can bring heavy snow, rain, and coastal flooding, especially from Virginia to New England. The most powerful nor'easters rival hurricanes in intensity.
Blizzard
A blizzard is a storm with sustained winds or frequent gusts of 35 mph or more and falling or blowing snow that frequently reduces visibility to below a quarter mile, lasting 3 hours or longer. The National Weather Service definition has no snowfall or temperature requirement: wind and visibility make a blizzard.
Barometric Pressure
The weight of the atmosphere pressing down on a given point, measured in inches of mercury (inHg) or millibars (mb). Rising pressure typically indicates improving weather, while falling pressure suggests approaching storms or precipitation.
Jet Stream
A jet stream is a relatively narrow band of strong wind in the upper atmosphere, typically around 30,000 feet, that blows from west to east. The polar jet sits between 50° and 60° latitude and the subtropical jet near 30°. Jet streams follow the boundaries between cold and warm air and steer the storm systems below them.
Post-Tropical Cyclone
A post-tropical cyclone is a former tropical cyclone that no longer has enough tropical characteristics to be classified as one. It can still bring heavy rain and strong winds. The two kinds are extratropical cyclones, which draw their energy from temperature contrasts between air masses, and remnant lows, which have winds below 34 knots (39 mph).
Cyclone
A rotating low-pressure weather system. Tropical cyclone terminology and intensity categories vary by region: in Australia, a tropical cyclone has maximum sustained winds of at least 34 knots (63 km/h, about 39 mph), averaged over ten minutes. The term does not universally require hurricane-force winds of 74 mph.
Bomb Cyclone: Guides and Explainers
These explainers connect this definition to real-world forecasting and decision-making.
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Sources
Explore Other Terms
VFR
Visual Flight Rules allow flight using visual references when the applicable visibility and cloud-clearance minimums are met. Those minimums vary by airspace class, altitude, and day or night under 14 CFR 91.155. Separately, the VFR weather category means a ceiling above 3,000 feet and visibility greater than 5 statute miles.
Invest
A weather system designated for investigation by the National Hurricane Center. An Invest designation triggers enhanced data collection and model runs but does not indicate expected development. Many Invests never become tropical cyclones.
Small Craft Advisory
A Small Craft Advisory is a National Weather Service alert for winds or seas that are hazardous to small boats in coastal and Great Lakes waters. The wind and sea thresholds are set separately for each geographic area. There is no precise definition of a small craft: any vessel that the conditions could affect counts.
Red Flag Warning
A Red Flag Warning is a National Weather Service alert that weather conditions could cause extreme fire behavior. It is issued when those conditions are occurring or expected within 24 hours. Typical criteria combine dry fuels with sustained winds of 15 mph or more and relative humidity of 25% or less, and exact thresholds vary by state and local office.
Polar Vortex
The polar vortex is a large area of low pressure and cold air surrounding each of Earth's poles. It always exists, weakening in summer and strengthening in winter. During Northern Hemisphere winter it often expands, sending Arctic air south with the jet stream and producing cold outbreaks across the United States.
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The Kp index is a 0 to 9 scale of global geomagnetic activity, reported in 3-hour intervals from ground-based magnetometers. A Kp of 5 or higher indicates a geomagnetic storm, and the values map onto NOAA's G-scale from G1 (Kp 5) to G5 (Kp 9). The higher the Kp, the farther from the poles the aurora can be seen.
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