Lightning tends to strike more often during rain because the presence of raindrops in the atmosphere can help create an electrical charge separation within clouds. Water droplets and ice particles collide in storm clouds, causing positive and negative charges to build up. The charges separate, with positive charges usually congregating at the top of the cloud and negative charges towards the bottom. When the charge separation becomes strong enough, a lightning bolt forms to equalize the charges between the cloud and the ground, or between different parts of the same cloud. So, the increased presence of rain in a storm can contribute to the conditions that lead to lightning strikes.
