Normal Climate Patterns

Part A: Planning for a Visitor

Your longtime pen pal from Australia has just written to you. He's planning to visit you next May and he wants to know what to bring for clothing and shoes. Will he need a rain jacket or sweatshirt? Can he plan on wearing sandals or will he need boots? In order to answer his questions, you try to remember what the weather was like last spring.

Talk with a lab partner about ways you might find out what "normal" May weather is like in your area.


You know that weather conditions in any area follow a typical pattern through the year. Your weather is different each season, but it can be expected to remain within a normal range of conditions for different times of the year. This repeating pattern of normal weather conditions that an area experiences over many years is known as climate.

Terms such as hot, windy, rainy, and humid are all descriptors of climate, but the two most important factors in climate are temperature and precipitation. When you respond to your pen pal, the two things that he'd really like to know are probably "How hot or cold will it be?" and "How likely is it to rain?"

  1. To generate and interpret graphs of an area's climate, go to the National Climatic Data Center's Divisional Data Interface ( This site may be offline. ) (link will open in a new window).
    • On the Data Retrieval page, click the "State" tab first (this seems to prompt the states to load) and choose your state, then click the "Division" tab.
    • Select a division or region of the state. In order to look at a range of locations, your teacher may assign a specific place for you to investigate.
    • Use the dropdown menus to select Starting and Ending dates that span the last full calendar year (January through December).
    • Click the Static Graphs radio button and select Temperature from the pull-down menu.
    • Next to the word "Show," make sure that "All Months" is showing.
    • Click Submit.

  2. On the graph that appears, read the axes labels and the legend to interpret what it means. Does this graph provide you with enough information to answer your pen pal?
  3. Use your browser's back button to go back to the Data Retrieval Page. Use the same selections as before, except for changing the Start Date two years earlier so that you request the last 3 years of temperature data.
  4. On the three-year temperature graph, check and record the values reported for each May.
  5. Go back to the Data Retrieval Page again. This time, request a static graph of precipitation for the last full year (January to December). Read the axes to interpret the graph. Look for patterns that indicate whether the region you are studying appears to have a rainy season or a dry season.
  6. Generate another graph to show three years of precipitation data.

    Stop and Think

    1. Do the two three-year graphs provide enough information for you to discover the "normal" temperature and precipitation levels for your region each May? Describe your reasoning.
    2. What other information could you use to characterize the climate?
  7. Go back to the Data Retrieval Page again. In the drop-down box next to the word Show, highlight "May" and set the Starting and Ending Dates to request May temperatures for the last 10 years.
  8. Do a Reality Check... Look to see if the values seem realistic. If they don't, try setting the month of the Starting Date to the same date as you are requesting. For example, to request May temperatures, set the month of the Start Date to 05.

  9. Explore the data by generating several more graphs, requesting temperatures and precipitation levels for various months over the full range of the data.

    Stop and Think

    3. List some of the things you learned in your exploration.
    4. What can you learn from the blue 1-year moving average and the red total average lines?
    5. Following your exploration, write your pen pal a brief description of the average conditions he can expect in May.