<AREA SHAPE=RECT COORDS="13,312,28,327" HREF="!The coalescence theory explains how different sizes of water droplets form in clouds. A droplet forms when water vapor condenses on a particle called a condensation nucleus. As a droplet falls through a cloud, it combines with smaller ones. When it becomes too heavy for the air to support, it falls as a raindrop.">
<AREA SHAPE=RECT COORDS="316,311,331,327" HREF="!The ice-crystal theory applies to clouds of supercooled water droplets. Such a droplet, formed by condensing water vapor, freezes on a particle called an ice nucleus. The resulting ice crystal combines with others to form a snowflake. The snowflake becomes rain when it falls through air warmer than 32 degrees F (0 degrees C).">
Weather experts have developed two theories of rain formation--the coalescence theory and the ice-crystal theory. These diagrams illustrate the processes described by each of these theories.<NP>
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World Book diagrams by Leonard E. Morgan</P>
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