Before you decide to do outdoor activities, it is importantthat you know what kind of weather it will be. If you look outand the sky is sunny without any clouds, you might predict,or be able to tell beforehand, what the weather will be likefor the next hour. However, just a look in the sky won’t tellyou what is in store for the next few days.

Meteorologists are the people who study weather. Theypredict what the weather will be like for the next few days.Before they can predict they have to collect information.

We have learned how to measure temperature, air pressure,precipitation, wind speed and direction, and humidity. Meteor-ologists collect this same information from many places, not justone. They know that the weather in other places influences theweather where we are.

Many meteorologists get this information from the NationalWeather Service. This is a government agency that has weatherstations collecting information from all over the U.S.

Weather balloons, radar, and satellites are three tools thatcollect information. Weather balloons collect information fromhigh in the air.

Radar sends radio waves into the air. They bounceoff of rain and snow. Radar is used to find where precipitationis and where it is moving.

Satellites high above the earth’s air collect and sendinformation about the weather all over the world.

Meteorologists need information about air masses to predict weather. An air mass is a large amount of air that hasthe same temperature and humidity. It can be warm or cold.It can have a large amount of water vapor or a small amount.Air masses are so large that two or three different air massescan cover most of the U.S.

Meteorologists also need information about fronts to predictthe weather. A front is the line where two air masses meet.The air masses do not mix together but stay separate.

A cold air mass often causes thunderstorms. Clouds from a warmair mass often cause a steady rain.

Meteorologists use information about the weather to predictwhat the weather is going to be like. This prediction is calleda forecast.

One way they predict weather is to look at the weather inthe west. Air masses that cause weather usually move fromwest to east.

Meteorologists know the kinds of weather that often happenwith certain air pressures, air masses, and fronts. High pressureareas often have fair weather. Low pressure areas often haveclouds and precipitation.

A warm air mass that comes from over the Gulf of Mexico might bring hot, humid weather on a summer day.A cold air mass from over Canada might bring coolerweather. Thunderstorms and snowstorms often happenat a cold front. Steady rain or snow often happen at awarm front.

Meteorologists study the direction air masses are moving.They study where high pressure areas and low pressure areasare moving. They try to predict what air mass, front, and airpressure are moving into your area. Then they predict what the temperature, chance of precipitation, and wind mightbe.