A mid-latitude cyclone forms when a

Position 1: Eventually the two fronts merge in a process called occlusion, cutting the storm off from its warm-air energy source and causing it to dissipate.

Position 2: Differences in temperature and pressure across this boundary cause the atmosphere to become dynamically unstable, initiating a rotating low-pressure system.

Position 3: Behind it, a faster-moving cold front undercuts the warm air, producing a narrower but often more intense band of convective rainfall and strong winds.

Position 4: A mid-latitude cyclone forms when a mass of cold polar air meets a body of warmer, moisture-laden air along a boundary called a frontal zone.

Position 5: As the cyclone matures, a warm front advances ahead of the storm centre, bringing widespread stratiform cloud and steady precipitation.