thunderstorms and tornadoes

hurricanes

blizzards and winter weather

clouds

web weather for kids
recipe for weather
combine ingredients

Remember some of the ingredients of weather?
Let's put them all together in the atmosphere.

If you look closely at the sections on temperature, pressure, volume, and density, you may notice that a relationship exists among these atmospheric variables. Atmospheric scientists express this relationship in one of two ways:

ideal gas law

This important relationship is called the "Equation of State" or "Ideal Gas Law" and can be used to help understand the atmosphere.

troposphere where the weather happens

The troposphere is the place in the atmosphere where our weather occurs - clouds, thunderstorms, tornadoes, hurricanes, and blizzards.

layers of the atmosphere

Check out the graph below to see how air density and air pressure change with altitude. Altitude is the distance above sea level.

Which of the following statements about the graph are true?

Air pressure is higher at lower altitudes.
True
False
Air density is higher at lower altitudes.
True
False
There is more space between air molecules at higher altitudes.
True
False
There is less oxygen to breathe at the top of a high mountain than there is at sea level.
True
False

Temperature changes with altitude, too!
Check out the graph below:

Which of the following statements about this graph are true?

 

If you follow the temperature line in the graph above from the surface of the Earth to the top of the atmosphere, moving to your left represents a decrease in temperature, to your right represents an increase in temperature, and straight up represents a constant temperature.

True
False
Temperature increases as you gain altitude in the Stratosphere and the Thermosphere.
True
False
Temperature decreases as you gain altitude in the troposphere and mesosphere
True
False
Air temperature varies in complicated ways with altitude.
True
False

What happens to air temperature in the troposphere as altitude increases?

As you climb a mountain, you can expect the air temperature to decrease by 6.5 degrees C for every 1000 meters you gain. This is called the standard (average) lapse rate.

If air temperature is 30 degrees C at sea level as shown above, you can expect it to be around 10.5 degrees C at air altitude of 3000 meters because of the lapse rate.

 

Plan an expedition!
You are going to climb Mount Audubon in Colorado today!

When you leave your house at 2000 meters, the air temperature is 15° C. What is the temperature likely to be at the 4000 meter summit?

10° C
28° C
2° C
7.8° C

Weather is strongly affected by changes in the lapse rate. That is because it determines how stable or unstable the atmosphere is.

   

 

   
    Click here to see how a marble and a bowl show examples of stable and unstable conditions!
       

Picture an invisible box of air called an air parcel. If we compare the temperature of this air parcel to the temperature of air surrounding it, we can tell if it is stable (likely to remain in place) or unstable (likely to move).

           
Check out these examples of stable and unstable air!
 
           

What Is Humidity?

There are three types of water.

  • When it is a solid we call it ice.
  • When it is a liquid we call it water.
  • When it is a gas we call it vapor.

These three different types of water are called states.

Water can change its state. When ice melts, changing into water, or when water evaporates, changing into vapor, a little heat is needed. When water freezes into ice or condenses from vapor to a liquid, a little bit of heat is released. The heat that is needed for or released from these changes in state is called latent heat.

Have you ever noticed that your skin feels cold when you get out of a swimming pool, lake or ocean on a windy day? It feels much colder than if you were dry. That’s because the wind helps the liquid water on your skin to evaporate becoming water vapor, and a little latent heat is needed for this change. In this case, the heat comes from you!

Measuring Humidity

Some people describe humid weather as muggy. The maximum amount of vapor that can be in the air depends on the air temperature. Warmer air can hold more water vapor within it. That’s why the muggiest days usually happen at the height of summer heat. But as the temperature goes down, the air can hold less vapor and some of it turns into liquid water.

In the pictures below, Dewdrop has a box that is one cubic meter in size. The air in the box is very humid when it is warm. Notice that as the temperature decreases, there is more liquid water at the bottom of Dewdrop’s box. That’s because the water vapor must come out of the air as it cools.

The amount of water coming out of the air is exaggerated in the picture above. In fact, the total amount of water in the warmest air, 1.85 grams, would only fill a measuring cup about 1/8 full.

What's the Dew Point?

Why are there water droplets on the grass on a cool summer morning, even though it did not rain the night before? The water most likely came from water vapor condensing from the air when it cooled to the dew point. The dew point is the temperature when water will start to condense out of the air.

The air in Dewdrop’s box above is always at the dew point, saturated as much as possible with vapor. However, usually air is holding less vapor than it actually could. If the temperature is 95 degrees and the air in Dewdrop’s box is only holding 0.44 cubic centimeters of water, how much would you have to lower the temperature to reach the dew point? To find the answer, take a look at Dewdrop’s box in the pictures above. What is the temperature when air is saturated with 0.44 cubic centimeters of water?

Calculate Relative Humidity

On a warm 76°F day, you measure that there is half a gram of vapor for each cubic yard of air.

At that temperature, air is able to hold 1 gram of water for each cubic yard of air. So what is the relative humidity?

Divide the amount of vapor in the air (0.5 grams) by the total amount the air can hold (1 gram) and multiply by 100 to figure out relative humidity as a percentage.

 


  What's a Weather Front?

An air mass is a large body of air that has similar moisture (density) and temperature characteristics. A front is a transition zone between two air masses.

A cold front is a warm-cold air boundary with the colder air replacing the warmer. As a cold front moves into an area, the heavier cool air pushes under the lighter warm air that it is replacing. The warm air becomes cooler as it rises. If the rising air is humid enough, the water vapor it contains will condense into clouds and precipitation may fall.

As the cold front moves, warm, moist unstable air is usually replaced by cold, dry stable air.

A warm front is the boundary between warm and cool (or cold) air when the warm air is replacing the cold air. Warm air at the surface pushes above the cool air mass, making clouds and storms. Warm fronts often bring stormy weather. Warm fronts often form on the east side of low-pressure systems where warmer air from the south is pushed north.

A warm front typically replaces cool dry air with warm moist air.

 


Now that you know some of the ingredients of weather,
pick some stormy weather from the links below!


[Temperature] [Pressure] [Volume] [Density] [Combine Ingredients]

[Thunderstorms & Tornadoes] [Hurricanes] [Blizzards & Winter Weather] [Clouds]

[Predict the Weather!]

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