U is for Umbrella.  I write this post on a rainy day in Athens.  Umbrellas are out for the purpose of protection from the rain.  Where I teach, in Sri Lanka, children are very familiar with umbrellas as they also serve the purpose of protection from the intense equatorial sun.  

Three or more large circles can represent a rain cloud.  I show the children that a crescent is made by covering a portion of a circle by another circle- then cutting away  the extra:

Children can draw a handle and raindrops.