Last updated: February 3, 2021
- Grade Level:
- Middle School: Sixth Grade through Eighth Grade
- Lesson Duration:
- 60 Minutes
- Additional Standards:
- NATIONAL/STATE STANDARDS:
Next Gen, MS-ESS2-5. Earth Science
Next Gen, MS-ESS2-6. Earth Science
Common Core, RI.7.1 Informational Text
- Thinking Skills:
- Remembering: Recalling or recognizing information ideas, and principles. Understanding: Understand the main idea of material heard, viewed, or read. Interpret or summarize the ideas in own words. Applying: Apply an abstract idea in a concrete situation to solve a problem or relate it to a prior experience.
How can we use clouds to predict the weather while in the field?
1. Students will be able to list factors that create weather (e.g. solar radiation, high vs. low pressure, weather fronts, etc.).
2. Students will be able to identify and describe three types of clouds with specific reference to field identification.
3. Students will be able to use clouds as evidence in a weather prediction statement.
Even though we might not think about it, we are all affected by weather every day. This is particularly evident in mountainous regions, where the weather can change suddenly and drastically. Have you ever planned a hike only to have the rain put a damper on your trip or traveled to see mountains only to experience clouds covering the peaks? Weather is always changing and developing, but if you know where to look, you can accurately predict the weather in the field. After this lesson you should have a better grasp on what the weather might do. Although weather prediction is not an exact science, it can give some generalities to help us predict what might happen next.
The large-scale movement of air masses around the earth is known as atmospheric circulation. The circulation of the earth's atmosphere is driven by solar radiation from the sun. Not all areas of the earth receive an equal amount of solar radiation. The atmospheric circulation redistributes energy from areas of surplus to areas of deficit. There are three circulation cells in each hemisphere that are responsible for this redistribution:
- Hadley Cell: low pressure near the equator causes air to rise, travel poleward, cool and sink at around 30 degrees latitude, and return to the equator. This cell is directly related to trade winds (prevailing winds that blow from east to west between 0 and 30 degrees latitude), tropical rainbelts, hurricanes, subtropical deserts and the jet streams.
- Ferrell Cell: high pressure near 30 degrees latitude causes air to sink, travel poleward, and rise when it reaches low pressure near 60 degrees latitude. This cell results in westerlies, or prevailing winds in the middle latitudes (between 30 and 60 degrees latitude) that blow from west to east.
Polar Cell: high pressure at the poles causes air to sink, travel towards the equator, warm and rise at around 60 degrees latitude, and return to the poles. This cell results polar easterlies, or the dry, cold, prevailing winds that blow from east to west between the poles and 60 degrees latitude.
As air is heated it expands and rises, creating areas of low pressure. As air is cooled it condenses and sinks, creating areas of high pressure. Wind is created as air travels from areas of high pressure to areas of low pressure. Travel is always in this direction. The Coriolis Effect, or the apparent deflection of weather patterns caused by the spin of the earth, influences the movement of air masses. In the Northern Hemisphere the Coriolis Effect deflects wind to the right, and in the Southern Hemisphere the Coriolis Effect deflects wind to the left.
- Low Pressure System: A low pressure system, or low, is a region where atmospheric pressure is lower than that of surrounding locations. Wind blows towards the low pressure system at the surface. When the air meets here it rises into the atmosphere and cools, causing water vapor to condense and clouds to form. Low pressure systems often result in precipitation.
- High Pressure System: A high pressure system, or high, is a region where atmospheric pressure is higher than that of surrounding locations. Wind blows away from the high pressure system at the surface. Air from higher in the atmosphere sinks to the surface to fill this void. High pressure systems often result in clear skies.
- Cirro- a prefix given to high clouds with bases above 20,000'
- Alto- a prefix given to mid-level clouds from 6,000'-20,000'
- Nimbo/nimbus- a prefix/suffix given to clouds that produce precipitation
- Cirrus- high and wispy
- Cumulus- puffy
- Stratus- blanket like covering
Basic Cloud Types:
- Cirrus- Lacy or wispy clouds that form from ice crystals at high altitudes and have a fibrous (hairlike) and/or silky sheen appearance. Cirrus clouds are relatively transparent and do not diminish the brightness of the sun when they cross it.
- Cirrostratus- Transparent, whitish veil clouds that form from ice crystals at high altitudes and have a fibrous (hair-like) or smooth appearance. Cirrostratus clouds are very extensive, nearly covering the whole sky. These clouds produce the appearance of a halo when covering the sun or moon.
- Cirrocumulus- Broken layer of small fleecy clouds that form at high altitudes from degraded cirrus/cirrostratus clouds. This cloud is thin and patchy and has a rippled or granulated appearance.
- Stratus- A generally gray cloud layer with a uniform base at low altitudes which may produce a rain or snow. When the sun is visible through this cloud, its outline is clearly discernible. Often when a layer of stratus breaks up and dissipates blue sky is seen.
- Altostratus- Gray or bluish cloud sheets at middle altitudes that totally or partially cover the sky. They are thin enough to regularly reveal the sun as if seen through a translucent object. Altostratus clouds occasionally cause very light precipitation.
- Nimbostratus- The continuous rain cloud, this dark gray cloud layer is found at a low altitude and produces falling rain or snow. It is formed from thickening altostratus clouds and is thick enough to blot out the sun.
- Stratocumulus- White or dark gray low altitude rounded masses of stratus that form lines, groups or waves. These clouds are often seen before or after severe weather. However, stratocumulus clouds generally do not produce precipitation, and when they do, it tends to come in the form of light rain or snow.
- Cumulus- Detached relatively low altitude rounded masses with a puffy, fluffy or cotton-like appearance. The sunlit parts of these clouds are brilliant white, while their bases are relatively dark and horizontal. Cumulus develops on days of clear skies due to convection.
- Altocumulus- White or gray patch, sheet or layered clouds, generally composed of rounded masses or rolls found at middle altitudes. Precipitation from these clouds is rare, and if it does fall, it does not reach the ground.
- Cumulonimbus-The thunderstorm cloud, this heavy and dense cloud is found at a low altitude in the shape of a towering mass. The upper portion is usually flattened into the shape of an anvil. The base of this cloud is very dark. Cumulonimbus clouds produce extreme weather including heavy downpours, lightning, hail storms, and tornadoes.
- Lenticular-Stationary, lens or saucer shaped clouds that form at high altitudes. Lenticular clouds develop when wind is forced up and over a topographic barrier, such as a mountain, that is oriented perpendicular to the wind direction. When sufficient moisture is present above mountain-top level, lenticular clouds develop.
- Water sprayer
Mountain Weather is a force that climbers and outdoor enthusiasts need to understand and predict in order to plan safely and make good decisions in the backcountry. Use this lesson to help students understand weather patterns and processes and learn field prediction.
Before we begin discussing the details of weather, we need to discuss why there is weather. Have a student volunteer help you demonstrate why weather exists by creating your own planet with its own weather. Use the globe as your planet. Create air on the planet by blowing on the globe or fanning it with a piece of paper. Heat from sunlight causes air to move around the earth, creating wind. Shine the flashlight on the globe to mimic the sun and create wind. Spin the globe to replicate the earth's rotation. Explain the Coriolis Effect and global atmospheric circulation (refer to the background section). Add moisture to the atmosphere by spraying the globe with the water sprayer. Water vapor makes up a tiny portion of the earth's atmosphere, but it causes most of our weather.
CloudsTeach a brief Weather 101 lesson so students have a base to build upon (refer to background section). Next discuss how clouds form. Clouds form when air cools to its dew point, or the temperature at which the air can no longer hold all of its water vapor. At the dew point, water vapor condenses into water droplets and clouds form. There are two mechanisms which can cause air to rise and cool to its dew point: convection and orographic lift. Radiation from the sun heats the earth and causes air to rise. This process is known as convection. Orographic lift occurs when an air mass is forced from a low elevation to a higher elevation as it moves over rising terrain (i.e. mountains). Orographic lifting causes rapid cloud formation and summer storms in Grand Teton National Park.
Clouds are the main environmental factor that we can use to help us predict the weather. Many of us already know that dark clouds likely mean that there is a chance of rain, but today we are going to take it a step further and learn how we can predict when those dark clouds will form. We will begin by learning the basic cloud types. Hand out the Cloud Card images to different students or groups of students and review cloud terminology. Read the name and description of each cloud type to the students and have them guess if they are holding the picture of the cloud you are describing. After reviewing the cloud types have students arrange the cards, sorting their clouds into high altitude, middle altitude, or low altitude categories.
Weather FrontsChanges in temperature, wind, precipitation and severe weather are often created by fronts, the meeting of two differing air masses. Warm fronts occur when warm air moves into a cooler area. Warm air slowly rises over the cooler air mass and replaces it. Warm fronts are typically preceded by steady precipitation and produce stratus clouds, as air is being forced to rise over a large area. After the warm front has passed, fair and mild weather can be expected. Cold fronts occur when cold air moves into a warmer area. As cold air moves in, it forces the warmer air to rise rapidly. This leads to the formation of towering cumulonimbus clouds and severe weather. Skies clear quickly after the cold front has passed and temperatures are cooler.
Weather PredictionNow that students have a basic idea of cloud types and weather, review how they can use clouds to interpret the weather:
- Cirrus = Fair weather, but change on the way
- Cirrostratus = Moist air, precipitation within the next 24 hours
- Cirrocumulus = Fair weather
- Stratus = Fair, but overcast
- Altostratus = Precipitation in near future
- Nimbostratus = Continuous precipitation
- Stratocumulus = Fair for now, potential storm brewing
- Cumulus = Fair
- Altocumulus = Fair for now, potential storm brewing
- Cumulonimbus = Severe weather (thunderstorms, hail, and tornadoes)
LightingLightning is an electrical discharge caused by an imbalance in charges. Lighting can be from cloud to ground, from cloud to cloud, or from cloud to air. Lighting is typically produced by cumulonimbus clouds. Lightning can be very dangerous, so it is important that you know how to react if you are caught in a lightning storm.
- Time visits to high risk areas with weather patterns
- Retreat to safer terrain if you hear thunder
- Avoid isolated trees
- Assume the lightning position (crouched down on the balls of your feet)
Weather LoreClouds are not the only way that we can predict the weather in the field as there are many other indicators that nature gives us which can help indicate what the weather might do. There are a lot of folklore sayings regarding weather prediction. Let's take a look at some of these and see what they mean.
Print the Weather Lore Sayings and cut them in strips. Have one student read the saying and the others guess what it means before reading the explanation.
Have students arrange the cloud cards, sorting their clouds into high altitude, middle altitude, or low altitude clouds or predictors of fair vs. inclement weather.
Weather Lore Sayings
Read Weather Lore Sayings and have students predict the weather.
Small Group Research and Presentation
Students gather in small groups of 4-5 people to research and present:
- What is the difference between weather and climate?
- What evidence of climate change exists in Grand Teton National Park? (Pikas, glaciers, and white bark pine are key areas where the park sees impacts of climate change.)
- What evidence of climate change exists in your own area?
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National Audubon Society Field Guide to North American Weather published by Alfred A. Knopf