Seasonal Weather Patterns

Scientists at the National Park Service keep records of the cherry blossom bloom date every year. They have noticed that the trees bloom around the same time each year, but the exact date shifts a little depending on the weather. In warm springs, the blossoms appear earlier. In cold springs, they arrive later.

This raises a big question: Why does weather follow a pattern that repeats every year, and how do living things respond to these seasonal changes?

• Why do you think the cherry trees bloom in spring but not in winter?
• What kinds of weather changes happen between winter and spring?
• If you wanted to predict when the cherry blossoms will bloom next year, what information would you need?

Weather describes what is happening in the atmosphere (the air around us) at a specific time and place. It includes temperature (how hot or cold it is), precipitation (rain, snow, sleet, or hail), wind, and cloud cover. Weather changes from day to day, but when scientists look at weather data over many years, they notice something important: weather follows a pattern that repeats with each season.

A season is a time of year that has typical weather conditions. Most places in the United States experience four seasons: spring, summer, fall (autumn), and winter. Each season lasts about three months, and together they make up a full year. The pattern of seasons repeats year after year — that is what makes it a seasonal pattern.

Your Investigation: Tracking Monthly Temperature

Imagine you recorded the average high temperature for your city each month for one full year. Below is a sample data set for a city in the midwestern United States (like Kansas City, Missouri). Study the data carefully — then we'll look for patterns.

Materials scientists use: Thermometers, rain gauges, weather stations, satellite images, and computer models that store decades of weather data.

Look at the bar chart above. Do you notice how the bars get taller from January to July, then get shorter again from July to December? That shape — rising and then falling — is the seasonal temperature pattern. This same pattern repeats every year!

When we look at the temperature data from our investigation, a clear pattern appears. Temperatures are lowest in winter (January and February), rise through spring, reach their peak in summer (July and August), and then drop again through fall. This is not a coincidence — it happens because of how much sunlight different parts of Earth receive during different times of the year.

In the summer, the sun appears higher in the sky and shines for more hours each day. This means the ground, water, and air absorb more heat energy. In the winter, the sun appears lower in the sky and shines for fewer hours, so there is less heat energy to warm things up. This change in sunlight is what drives the entire seasonal cycle.

But temperature is only part of the picture. The type of precipitation also follows seasonal patterns. When temperatures drop below freezing (32°F), precipitation falls as snow or sleet instead of rain. That is why snow is common in winter but rare in summer. Spring and fall often bring a mix, as temperatures shift between warm and cold.

Now let's connect this back to our anchoring phenomenon — the cherry blossoms in Washington, D.C. The cherry trees need a period of cold winter weather (called a chilling period) before they can bloom. Then, when spring temperatures warm up enough, the trees "wake up" and produce flowers. This is why the blossoms appear in spring and not in any other season. The trees are responding to the seasonal weather pattern.

If a particular year has an unusually warm February and March, the cherry blossoms may bloom earlier than usual. If spring comes late and stays cool, the blossoms are delayed. The trees are evidence that seasonal weather patterns are real and that living things depend on them.

The crosscutting concept in this lesson is Patterns. Scientists look for patterns in data to help explain and predict what will happen. Seasonal weather is one of the most important patterns on Earth — and it isn't the only pattern we see in nature!

Patterns show up across all areas of science. When scientists spot a pattern, they can use it to make predictions about what will happen next. Let's look at how the concept of patterns appears in different parts of science.

Understanding seasonal weather patterns is not just useful for scientists — it matters for everyone. People have used knowledge of seasonal patterns for thousands of years to solve real problems. Here are some examples of how seasonal weather knowledge is used in the real world:

Think about it: What features would you include in your design? You need to think about hot summer sun, cold winter winds, spring rain, and falling leaves in autumn. How could your design protect students from each season's typical weather while still being outside?

Some ideas to consider: A roof or canopy for rain and sun, walls that can open in warm weather and close in cold weather, a heating system for winter, and fans or shade structures for summer. Engineers think about seasonal weather patterns every time they design outdoor spaces!

• Weather — The condition of the atmosphere at a specific time and place, including temperature, precipitation, wind, and cloud cover.
• Season — A time of year (spring, summer, fall, or winter) that has its own typical weather conditions. Each season lasts about three months.
• Temperature — A measurement of how hot or cold something is, usually measured in degrees Fahrenheit (°F) or Celsius (°C).
• Precipitation — Water that falls from clouds to the ground, including rain, snow, sleet, and hail.
• Pattern — Something that happens in a regular, repeating, and predictable way. Seasonal weather follows a yearly pattern.
• Meteorologist — A scientist who studies weather and uses data to make weather predictions (forecasts).
• Data — Information collected through observations and measurements. Scientists analyze data to find patterns and draw conclusions.
• Predict — To use evidence and patterns to say what you think will happen in the future.