When rain and snow fall from the sky in colors of the rainbow rather than clear or white, it might be a bit alarming. Centuries ago, our ancestors believed “blood rain” and other strange weather events were bad omens. Today, meteorology explains they have less to do with catastrophe and more to do with a common nuisance visitor: dust.
The Dirt on Dust
No, dust isn’t just found in the hidden corners of your home or under your bed. Dust also exists outdoors. Sand, soil, salt from sea spray, pollen, algae, soot, and ash are all sources of tiny outdoor particles called “aerosols.” In fact, this is where most household dust originates.
However, unlike household dust, you probably won’t pay much attention to aerosols when you’re outside. They are not only less than a millimeter in size, but they often travel high above our heads in the upper atmosphere.
So How Does This Dust Color Rain or Snow?
Winds from low-pressure systems and weather fronts carry these aerosols over great distances—from one city, state, or country to the next—unbeknownst to us. Along the way, these dust clouds meet and mingle with actual clouds, and as raindrops or snow crystals fall through aerosol plumes, they attract the dust-like particles on their way to the ground. It’s the reason why the air feels cleaner after a rainstorm. If the aerosols that dissolve in rainwater and snow moisture are highly pigmented, they’ll actually stain raindrops and snowflakes in midair.
What colors you’ll see in the rain or snow depend on the minerals present in the aerosols. If the dust contains iron oxides, the precipitation will appear in shades of red and orange, similar to the landscape on Mars, resulting in “red rain” or “blood rain.” If the aerosols are rich in sulfates, the precipitation will have a sunny yellow hue. On the other hand, if the air is filled with soot, the rain or snow might be ink-colored.
The intensity of the colors in the precipitation depends on the thickness of the dust plume or the duration of the rain or snow shower. Light dust concentrations may produce pastel-colored precipitation, such as pinks and butter yellows, which can coat your house, car, and outdoor furniture.
Is Red Rain Dangerous To Plants?
Seeing plants and trees outdoors covered with vibrant rainbow-hued rain and snow can be quite concerning, especially for gardeners. However, it is important to note that colored precipitation does not usually pose a toxic threat to vegetation. In fact, many of the minerals that give color to rain or snow, such as iron oxide and sulfates, are micronutrients that are essential for the healthy growth of flowers and crops.
There is no need to worry about your plants receiving an excessive amount of these beneficial micronutrients. Blood rains, which contain a higher concentration of micronutrients, occur very rarely – typically only a few times a year in Europe, and even less frequently in the United States and Canada. Therefore, the boost in micronutrients they receive is generally not a cause for concern.
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Tiffany Means is a freelance writer and a degreed meteorologist. She specializes in weather forecasting and enjoys making the subject of weather (and the science behind it) more relatable. She currently resides in the Blue Ridge Mountains of North Carolina.