Can there be a sun-snowshower?

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Can there be a sun-snowshower?

Photo: Zaphod
These cumulus clouds are not sunshower material. See a late spring sun-snow shower here!

Almost all of us have noticed a summer rainshower that occurs while the sun is shining on us. In this event, known as a sun-shower, the raindrops fall from a type of cloud called a cumulus cloud.

Cumulus clouds are a manifestation of the process of convection. The atmosphere can induce convection when the surface temperature is much higher than the air temperature some distance above the surface. This can happen when the day heats up in summer or when very cold air moves over an unfrozen lake in winter. This condition can destabilize the atmosphere’s normal stratification, causing cumulus clouds to shoot upward quickly and produce precipitation in a short time. These clouds are very local and so an individual cumulus may be surrounded by clear sky. Precipitation dropped from the base of these clouds takes time to reach the surface.

Sunshowers occur when the precipitation from such an isolated cumulus hits the surface after the cloud has moved away. Though less common in winter, sun-snowshowers do occur and they are a result of the same process. Those of you who live in areas prone to lake effect snows have probably experienced sun-snowshowers more than once. Here in the land of cheese and beer, they are a rarity but keep your eyes peeled – sun-snowshowers do happen!

Steven A. Ackerman and Jonathan Martin are professors in the Department of Atmospheric and Oceanic Sciences at UW-Madison, are guests on the Larry Meiller‘s WHA-AM radio show the last Monday of each month at 11:45 a.m.