Weather Matters

By Eve Pranis

Weather describes the variations that occur in the atmosphere from day to day, while climate refers to the typical weather found in an area based on years of observations.

To understand these concepts, it helps to understand what influences climate. The most important factors are how warm an area is and the amount of precipitation it gets. This, in turn, has a big influence on the plants and animals that live there. Nearness to the equator is the most important factor, affecting the amount of sunlight, and thus warmth, that an area receives. Because of the angle at which the sun's rays strike the earth, the equator, which receives direct rays that pass through less atmosphere, is warmer than locations nearer the poles.

Other factors that affect weather and climate are proximity to water (particularly an ocean), direction of prevailing winds, and relief (e.g., mountains). Consider, for instance, how these factors influence climates in this country. The coasts tend to have more moderate weather, with relatively cool summers and mild winters, and less of a temperature range than the center of the country. This occurs because the ocean, though it warms slowly, holds heat and releases it more slowly than does land, moderating the air temperature. The Midwest experiences cold winters and very hot summers because the expanse of land heats more quickly and cools more rapidly than water. It also tends to be drier in the center of the country, since prevailing winds from the west have lost most of the moisture gained over the ocean. Mountain areas tend to get cooler temperatures and more rainfall since thinner air is less able to absorb and retain heat, and can hold less water. The Southeast, nearer the equator, has hot summers and short, mild winters, and remains fairly humid. The Southwest, though warm, is much drier since warm moist air cools as it rises over the western mountains and drops its moisture. The descending air is warm, but has little remaining moisture.

Weather Up Close: Exploring Microclimates

Ask your students if they have ever sought respite from the heat under the cooling shade of a tree. If so, they've enjoyed a microclimate.

Invite the class to brainstorm what the word microclimate might mean, then try to agree on a definition or description. If necessary, explain that it refers to the climate of a small, local area that differs from the general climate because of differences in sun/shade, temperature, wind, or moisture. Ask, What factors might affect the climate in a given location? Then have small groups investigate the school grounds, find places they think might have different microclimates, and describe each location. If you have the equipment, encourage groups to measure rainfall or temperature differences in these areas. Which is the warmest? Coolest? What might have caused the differences (e.g., a building may provide shade and wind protection, dark soil absorbs more heat)?

Factors that can affect microclimates include manmade features like buildings and roads, geographical features like rocks, slopes, or water runoff channels, or living things like trees or meadows. A garden site on the south side of a building or slope may get more sun and be much warmer than one on the other side, for instance.

Investigate Plant Preferences

Ask your class how they think different microclimates around the school might affect the growth of plants. Have them provide a rationale for their answers (for example, plants might grow more quickly in spot A, because it gets more sun and moisture). How might they test or verify their hypotheses? For instance, a group of students might start several containers of one type of seedling (e.g., radishes, tomatoes, or marigolds) using the same soil mix, container size, and so on, then place each in a different location. They could track rainfall, soil, air temperature, and so on, then chart the growth and development of plants in each site. What can you infer about the effect of the microclimate on plant growth? Were there other factors that might have influenced the outcome?

Take Soil Temperatures

Is the soil temperature the same as the air temperature? How might soil temperature affect plants? Invite students to explore soil from different spots in the schoolyard. Do some types of soil seem to warm up more quickly in the spring than others? What are their characteristics? Have students use soil thermometers to compare different types of soil, then consider factors that seem to influence soil temperature. (Students may discover, for instance, that dark soil absorbs more heat than light-colored soil or that wet soil remains colder than dry soil in the spring.) Help them grasp the concept that the earth's surface heats up differentially, resulting in different types of air masses that interact to affect climate.

Create a Garden Weather Station!

Meteorologists study the weather by recording data using a range of instruments, then analyzing their findings. Consider cultivating keen weather watchers by building your own garden or schoolyard weather station.

A wooden or plastic weatherproof box can serve as protection for your homemade or purchased instruments.

Water is vital to plant growth, so one of the weather factors that most concerns gardeners is rainfall. (A good rule of thumb is that garden plants should receive an inch of water a week.) Challenge students to come up with suggestions for building a rain gauge to track the amount of precipitation in a given time period. For instance, find an old coffee can to hang out at your weather station, then mark a clear plastic straw with inches or centimeters (and fractions). Once a week, insert the straw to the to the bottom of the can, put your thumb on top, and withdraw it to read the depth of rainfall. Or make a tagboard ruler and place it inside a clear glass jar. Cover the ruler with clear cellophane or a sandwich bag and tape it at the top to keep it upright.

Other weather instruments you can purchase from science suppliers or make in the classroom include a psychrometer (to measure relative humidity), a barometer (to measure air pressure), a hygrometer (to measure humidity), a ventemeter (to measure wind speed), a weather vane (to determine wind direction), and a minimum/maximum thermometer (to measure temperature range). For guidelines for creating some of these instruments from readily available materials, check out the following Web site: (

Blowin' in the Wind

An easy way to estimate relative wind speeds is to use the Beaufort Scale. This system was developed to estimate wind speeds on the ocean, and later adapted for land use. Consider having your young wind watchers use the following scale, or create a similar system themselves.

Observation-----------------------------------Wind Description (speed)

smoke rises vertically---------------------------calm

smoke drifts----------------------------------------weather vane inactive;1-3 mph

leaves rustle, can feel wind on face--------light breeze (4-7 mph)

leaves and twigs move, light flags

extend; gentle breeze--------------------------(8-12 mph)

moves small branches, raises dust

and paper; moderate breeze-----------------(13-28 mph)

whole branches swaying; strong breeze--(25-31 mph)

Explore the Lore!

Challenge students to consult families, gardeners, and weather resources for examples of weather "lore." Which sayings might have some scientific basis, and which are merely fanciful? Ask students how they might research or test the accuracy of these assertions. Some examples follow.

* If it thunders on All Fool's Day, it brings good crops of corn and hay.

* Red skies at night, sailor's delight. Red skies at morning, sailors take warning.

* If the woolly worm's head is more black than colored, the coldest part of the winter will come in the first months of winter.

* If oaks bud earlier than ash trees, it will be a wet summer; if ash buds first, it will be dry in July and August.

* When you see a mackerel sky, 'Twill not be many hours dry.

* When it rains before seven, 'Twill clear before eleven.

Weatherwise School Gardens

"My seventh graders had created a blueprint for their dream school garden, but realized they'd have to revise their plans once they thought about the amount of sun required by their proposed plants," reports Lostant, IL, teacher Jean Smith.

Jean's students had learned enough about climate to know that the sun would shift positions throughout the year, and realized they hadn't factored that into their initial plan. In March, the students investigated where the school building's shadow hit the garden site, then used what they knew of the sun's movement to predict where the shade would fall in the summer. Each week, the students drew an additional line on their original blueprint, showing how the building shadow was progressing. "We used our predictions of where the shade would hit to rethink which plants we put where in the garden, based on how much sun each required," explains Jean.

School gardeners have lots of opportunities to think about the influence of climate and weather. Although your students might like to grow bananas in their school garden, for instance, chances are that your growing season and climate conditions wouldn't permit it. How does our climate affect what we can grow and when we can grow it? How can we find a site that offers at least six hours of sun a day? When is the danger of frost past in the spring? Can we extend the season so we can garden earlier in the spring? As your class plans to grow plants indoors and out, seize the opportunity to examine how gardeners notice and work with the climate and modify conditions for plants.

Zoning In

Many seed catalogs, packets, and gardening resources depict charts or maps indicating conditions -- first and last frost dates, average minimum temperatures, or amount of sunshine or rainfall -- in different climatic zones throughout the country. A commonly used map type assigns zone numbers indicating which perennial plants can adapt to each area. If the winter temperature in your area dips below a certain temperature, for instance, certain tender perennials will simply not survive. Excessive summer heat can also spell the end of certain plants.

Invite students to use gardening references or Internet resources to examine different climatic zones throughout the U.S. Brainstorm which geographic factors might influence the climate and, in turn, zone designations. Some of the factors influencing climate are proximity to equator (latitude), oceans, mountains, and so on. Ask, Do the temperatures in your schoolyard or garden reflect those in your zone? Have students regularly measure high and low temperatures in these locations, then compare these with temperatures in your local paper. Is your garden (or other spot) warmer or cooler? What factors do you think might affect this? How does this affect what you might be able to grow?

Plant Cover-ups: The Greenhouse Effect

Unlike many individuals, gardeners are people who actually do something about the weather. That's because we like to extend mother nature's growing season and we enjoy growing plants that are not naturally adapted to our climates. (For instance, tomatoes, a favorite garden crop, are actually native to tropical regions of South America.) Many gardeners use strategies for extending the season and protecting plants from frost and cold temperatures. Cold frames, plastic milk jugs, and plastic or nylon row covers keep sun-warmed air around plants and soil, prevent frost from settling on plant leaves, provide wind protection, increase humidity, and may protect plants from insects.

All these plant protectors operate on the same basic principle. Radiant (light) energy from the sun can pass through transparent and semi-transparent materials. When the light arrives inside a closed space, it is absorbed by the surfaces within, then radiated again as thermal (heat) energy. The heat energy is less able to pass through the materials, so heat is trapped inside. This energy warms the air, encouraging plant growth.

As a simple but powerful exploration of this phenomenon, invite students to place a thermometer inside a clear, covered glass jar in the sun. Place a second thermometer next to the jar. After half an hour, compare the two temperatures. Once students have explored this concept, invite them to try designing plant protectors for their seedlings. Have them compare different types of designs, predicting and then monitoring differences in temperature and plant growth rates. (Although there are many commercial products available, homemade gadgets can provide a good design challenge for students.) Be sure that students also consider other plant needs as they create and monitor their setups. For instance, Is the temperature too high under the plant protector? How can we provide ventilation? How can we ensure that plants get enough water?

Predicting Frost

Concerns about frost damaging precious plants run high in the spring and fall for many school gardeners. Challenge students to check with gardening references, area gardeners, the Cooperative Extension Service, or other local sources to find out the typical last spring frost or first fall frost in your area.

Regardless of the weather station's prediction on a given day, the microclimate in each garden is unique. Invite your young sleuths to use what they've learned about factors that influence weather to try to predict when a frost might occur.

When the sky is clear and there is low humidity, temperatures may drop enough to cause frost. (Without clouds to act as a blanket, the earth loses heat to the atmosphere.) To more accurately predict frost, students can find out the dew point from the weather forecast. When air cools to the saturation point (can no longer hold water vapor), the vapor condenses and forms dew. If the air temperature is below the dew point and below freezing, frost occurs.

If your students are concerned about frost, but don't have enough sheets or other materials to protect the whole garden, encourage them to discuss which plants might need the most protection, and why. (Typically, crops like tomatoes and peppers that originated in warmer climates are the most sensitive to frost. Crops adapted to cooler conditions, such as spinach, lettuce, and broccoli, can handle modest frosts without damage.)

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