Extratropical cyclone

Lore & Background

Extratropical cyclones form anywhere within extratropical regions, usually between 30° and 60° latitude, through cyclogenesis or extratropical transition. Cyclogenesis occurs along linear bands of temperature and dew point gradient with significant vertical wind shear, classified as baroclinic cyclones. Initially, low pressure forms near a favorable quadrant of an upper-level jet streak, where divergence causes air to rush out from the top of the air column, reducing surface pressure and strengthening the cyclone. As the cyclone strengthens, the cold front sweeps toward the equator and around the back of the system, while the warm front progresses more slowly. Eventually, the cyclone occludes as the cold front overtakes part of the warm front, forcing a tongue of warm air aloft, and the cyclone becomes barotropically cold and weakens. Tropical cyclones often transform into extratropical cyclones at the end of their tropical existence, usually between 30° and 40° latitude, through extratropical transition. During this process, the cyclone forms or connects with nearby fronts, its size increases, its core weakens, and its primary energy source shifts from latent heat release to baroclinic processes. The cyclone loses its warm core and becomes cold-core. On rare occasions, an extratropical cyclone can transform into a tropical cyclone if it reaches warmer waters and less vertical wind shear. The Joint Typhoon Warning Center uses the extratropical transition (XT) technique to estimate intensity of transitioning cyclones based on satellite imagery.

Reader's Guide

Extratropical cyclones are fundamental to understanding mid-latitude weather patterns, as they are the primary drivers of day-to-day weather changes across large portions of Earth. Their ability to produce a wide range of conditions—from mild showers to severe thunderstorms, blizzards, and tornadoes—makes them critical for weather forecasting and hazard preparedness. The study of these cyclones has revealed that they form along temperature and dew point gradients (frontal zones) and are influenced by upper-level jet streaks, with explosive cyclogenesis occurring when pressure drops more than 1 millibar per hour. Their transition from tropical cyclones and occasional transformation back into tropical systems highlights the complex interactions between different cyclone types. Understanding extratropical cyclones is essential for predicting severe weather events, maritime safety, and climate studies, as they influence temperature, precipitation, and wind patterns across the mid-latitudes.

Did You Know?

• Extratropical cyclones are capable of producing severe hail, thunderstorms, blizzards, and tornadoes.
• When atmospheric pressure falls more than 1 millibar per hour, the process is called explosive cyclogenesis, and the cyclone can be described as a bomb.