What is explosive cyclogenesis, and how fast must pressure fall?

What does cyclogenesis mean?

Cyclogenesis is the formation or strengthening of a cyclonic circulation. In the middle latitudes, it usually involves an extratropical low, a system associated with temperature contrasts, weather fronts and the movement of air through the atmosphere.

When the low deepens especially quickly, the process is called explosive cyclogenesis. You may also hear a storm undergoing this process called a “weather bomb”.

How far must the pressure fall?

The classic threshold varies with latitude. At 60° latitude, the reference value is a drop of at least 24 hectopascals (hPa) in the central pressure of the low in 24 hours. At the latitudes of mainland Spain, the equivalent threshold is lower, roughly 18–20 hPa in 24 hours depending on the storm track.

Why can the winds become so strong?

As the low deepens, pressure differences over a given distance often increase and the circulation strengthens. Surface winds also depend on the structure of the storm, elevation, atmospheric stability and local terrain. Large waves and precipitation are possible, but the effects vary from storm to storm.

Three common misunderstandings

• “Explosive cyclogenesis is heading our way.” The storm moves from place to place. Cyclogenesis describes how it forms or intensifies along its track.
• “It must be a hurricane.” Extratropical lows and tropical cyclones have different structures and draw their energy in different ways.
• “Explosive means catastrophic.” The term describes the rate of pressure fall. Estimating damage requires knowing where the strongest winds, waves and rain will reach.

How to follow a storm on Meteorix

1. Locate the low-pressure centre and follow how its position and central pressure change.
2. Look at the isobars and compare their spacing with the areas of strong wind in the forecast.
3. Check forecast gusts, Global Risk and official warnings to assess potential impacts.