Lesson 6: Fog, Dew, and Precipitation
Getting Started
Have you noticed how closely connected the water cycle and the weather are? Weather keeps the water cycle going, and water keeps weather cycles going. Water currents affect air temperatures, which create wind, and water is the reason we experience certain kinds of weather (like storms, precipitation, clouds, and fog).
So far you have seen how water evaporates to enter the air as water vapor and how water vapor condenses in the sky as clouds. Today you will read about fog and dew, which use water vapor in the air to form condensation close to the ground. Then you will look at what happens when water, or precipitation, comes down from the sky as rain, hail, sleet, or snow.
Weather journal: Record the following data in your weather journal for today: temperature, air pressure, precipitation, wind speed and direction, relative humidity, and wind chill or heat index information, if applicable. For the Cloud Description column, look for one cloud in the sky that is easy to identify. On days when the clouds are too hard to identify, describe the day's cloud cover more generally. If you notice early-morning fog or dew (today or in the future), be sure to mention that in the notes section of your weather journal as well. Use today's clouds and/or air pressure reading to forecast the weather for later today or tomorrow.
NOTE: Look ahead to the instructions for Lesson 7, Activity 1. Water with blue food coloring will need to be frozen for the activity. You may want to put the water in the freezer today so it's ready for tomorrow.
So far you have seen how water evaporates to enter the air as water vapor and how water vapor condenses in the sky as clouds. Today you will read about fog and dew, which use water vapor in the air to form condensation close to the ground. Then you will look at what happens when water, or precipitation, comes down from the sky as rain, hail, sleet, or snow.
Weather journal: Record the following data in your weather journal for today: temperature, air pressure, precipitation, wind speed and direction, relative humidity, and wind chill or heat index information, if applicable. For the Cloud Description column, look for one cloud in the sky that is easy to identify. On days when the clouds are too hard to identify, describe the day's cloud cover more generally. If you notice early-morning fog or dew (today or in the future), be sure to mention that in the notes section of your weather journal as well. Use today's clouds and/or air pressure reading to forecast the weather for later today or tomorrow.
NOTE: Look ahead to the instructions for Lesson 7, Activity 1. Water with blue food coloring will need to be frozen for the activity. You may want to put the water in the freezer today so it's ready for tomorrow.
Stuff You Need
- Eyewitness Weather by Brian Cosgrove (revised edition)
- colored pencils or watercolor paints* (Activity 2 - Option 2)
- empty two-liter bottle* (Activity 3 - optional)
- ice
- large metal can
- marbles or small rocks* (Activity 3 - optional)
- masking or painters tape* (Activity 3 - optional)
- permanent marker* (Activity 3 - optional)
- ruler* (Activity 3 - optional)
- scissors* (Activity 3 - optional)
- spoon
- thermometers (kit)
* - denotes an optional material that may or may not be needed
Ideas to Think About
- What affects the daily weather or the climate in your environment?
- How predictable are weather cycles?
Things to Know
- Precipitation is water that comes down from the sky as rain, hail, sleet, or snow.
- The dew point is the temperature where the air cannot hold any more water vapor. On Earth, this causes dew or fog. In the sky, this causes clouds.
- Dew is water vapor that has condensed on grass and plants.
- Fog is water vapor that has condensed in the air. It is a cloud that has formed at the Earth's surface rather than higher up in the atmosphere.
- A rain gauge is a tool that shows how much rain has fallen during a storm or during a specific day.
Skills
- Know that water vapor in the air moves from one place to another and can reappear as a liquid when cooled (fog, clouds, dew, and rain), or as a solid if cooled below the freezing point of water (snow, hail, sleet). (S)
- Investigate the water cycle, including the processes of evaporation, condensation, precipitation, and runoff. (S)
- Determine and discuss how the following are interrelated: dew point, relative humidity, temperature. (S)
Introducing the Lesson
So far your child has looked at how water vapor hangs in the air as humidity and condenses in the sky as clouds. This lesson will help your child understand how water is forced out of cooling air or more humid air to form dew, fog, or precipitation.
NOTE: Look ahead to the instructions for Lesson 7, Activity 1. Water with blue food coloring will need to be frozen for the activity. You may want to put the water in the freezer today so it's ready for tomorrow.
NOTE: Look ahead to the instructions for Lesson 7, Activity 1. Water with blue food coloring will need to be frozen for the activity. You may want to put the water in the freezer today so it's ready for tomorrow.
Materials: Eyewitness Weather by Brian Cosgrove (revised edition)
Read pages 48-49, 20-21, 30-31, and 40-41 in the book Eyewitness Weather by Brian Cosgrove. Answer the following questions:
Questions
- What is frost?Frost is water vapor from the air that has frozen.
- How does fog form?Fog forms when air near the ground cools, causing the water vapor in the air to condense into small droplets.
- About how much snow must fall to equal 1 inch of rain?About 12 inches of snow equals 1 inch of rain.
- Under what conditions do the heaviest snowfalls occur and why?In areas where the air temperature is around freezing. (Southern Canada and the northern U.S. are examples). If the weather is too cold (as at the North Pole), the air cannot hold enough moisture to produce snow.