A spinnerbait is a fantastic bait to use in the rain year round. Partly for the same aforementioned reason, it’s constantly on the move and can therefore be used to cover a lot of water. But it also has a good amount of flash from the blades and can be fished at various heights in the water column so you can burn one with double willow leaf blades just below the surface in the summer and slow roll one with double Colorado blades in the winter.
The light is obviously low in a rainy situation, but even more so below the surface of the water. When the water is slick like glass, light penetrates the water’s surface pretty well. When the surface is broken up by rain drops and wind, the light has a much harder time penetrating the surface and illuminating what’s beneath. Both the vibration of a spinnerbait and its flash help the fish locate the bait in these lowlight scenarios.