Sun and Clouds:
Percent Sunshine

Where in the United States does the sun shine the most? Government scientists keep weather records about how much sunshine major cities get each month. Which are the "sunniest" cities in the United States? Go on, take a guess.

Set A:	___ Honolulu, HI	___ Chicago, IL	___ San Diego, CA
Set B:	___ Key West, FL	___ Los Angeles, CA	___ St. Louis, MO
Set C:	___ Juneau, AK	___ Philadelphia, PA	___ Atlanta, GA
Answers:	Set A = San Diego	Set B = Los Angeles	Set C = Atlanta

The point in asking about patterns on the map is to make students aware of conditions that influence their exposure to the Sun's radiation.

As students examine the results of putting the percent sunshine data on the United States map, two general tendencies should emerge. The first is, of course, the states in more southerly latitudes are exposed to more solar radiation overall. The second general pattern is less pronounced. States in which prevailing weather patterns supply less atmospheric moisture experience a higher percent daily sunshine. For example, in the southwestern states, moisture from the Pacific Ocean is typically blocked by the western mountain ranges, and these states are also too far west to be influenced by moisture flow from the Gulf of Mexico, which often supplies atmosphereic moisture to eastern states. In general, if the two trends conflict—as they do in Florida, for example—the latitude factor seems to be the stronger of the two.

Relevant National Science Education Standards

Unifying Concepts and Processes — The activity involves understanding of how different factors in the climate system interact to produce the weather of a particular region.