The experience of rain falling from a clear sky while the sun shines brightly is a meteorological event known as a sun shower. This phenomenon combines two weather elements that usually occur separately: clear skies and precipitation. A sun shower is a brief, localized rain event that happens when a patch of sky remains unclouded enough for sunlight to reach the ground, even as water droplets fall. The simultaneous presence of direct sunlight and falling rain creates a visually striking scene.
The Science Behind Sun Showers
The physical explanation for a sun shower centers on the localized nature of precipitation and the effect of atmospheric currents. Rain is produced by individual, relatively small cloud formations, such as cumulus clouds, which release moisture over a limited area. When these clouds are isolated, they can generate rain without covering the entire sky, allowing the sun’s rays to stream through the surrounding clear patches.
A factor in separating the rain from its parent cloud is wind shear, which is the difference in wind speed or direction. Strong winds aloft can push the falling rain a considerable distance horizontally from the cloud base. This creates what is sometimes called a “rain curtain” that drifts into an area where the sky above is completely blue and the sun is unobscured.
The rain-producing cloud does not need to be directly overhead for the sun’s light to illuminate the falling drops. The sun’s angle also plays a role, especially when it is lower in the sky during the morning or late afternoon. At these times, the sun’s rays can enter the lower atmosphere at a shallow angle, passing underneath the rain cloud to shine on the precipitation. This separation of cloud and rain allows the dual appearance of bright sun and falling water.
Global Names and Folklore
The unusual sight of a sun shower has inspired a variety of imaginative interpretations. In many places, the phenomenon is explained through the metaphor of a secret or unusual wedding. This theme of a contradictory union reflects the paradox of rain and sun occurring together.
In Japan, the event is known as a kitsune no yomeiri, or “the fox’s wedding.” A similar animal-centric belief exists in parts of Africa, where sun showers are colloquially referred to as a “monkey’s wedding.”
Other traditions ascribe the weather to folkloric figures, often with a mischievous or temperamental nature. In the Southern United States and the Caribbean, one common saying is that a sun shower means “the devil is beating his wife.” Meanwhile, in parts of Europe, old traditions suggest the rain is caused by witches, such as the Catalan belief that it happens when “witches are combing their hair.”
The Optics of Rainbows
Sun showers are associated with rainbows because they provide the ideal conditions for this optical display. A rainbow requires two simultaneous elements: direct sunlight and airborne water droplets. The rain shower supplies the necessary spherical water droplets, and the clear sky ensures the sun is shining.
The formation of the rainbow arc involves a precise sequence of light physics within each raindrop. As sunlight enters a spherical drop, it first refracts, or bends, and simultaneously disperses into its component colors. The light then reflects off the back interior surface of the drop and refracts a second time as it exits the water and travels toward the observer’s eye.
For a person to see a rainbow, the sun must be positioned directly behind them, and the rain must be falling in front of them. The light is scattered back toward the observer at an angle of approximately 42 degrees, with each color separated due to its unique wavelength. The localized rain of a sun shower, with the sun shining from one direction, often creates this perfect alignment, resulting in the brilliant spectral arc.