Science Lesson 20

Environmental Science 5
Lesson 20
CLOUDS AND STORMS
At some time you have probably watched the clouds go by, and seen animals or shapes. Let's go more in-depth into cloud formations and what kinds of weather they bring. How do clouds form? As warm air passes over the ocean or large lakes, it picks up water vapor. Since warm air is not as heavy as cold air, it will rise as it gets warmer. Then, as the air rises, it cools, since the atmosphere is colder the higher up you go. The temperature at which air can no longer hold the water that it contains is called the dewpoint. When the dewpoint is reached, the water condenses, or "drops out" to form dew or clouds. These clouds change shape as parts evaporate, or are moved and re-shaped by the wind.

1. Try this: Fill a can 2/3 full with ice and water. Place a thermometer into the ice/water mixture. As soon as condensation forms on the outside of the can, read the temperature on the thermometer. This is the dewpoint of the air in your room.

We don’t have a thermometer.

Weather forecasters talk about the dewpoint because it affects how we feel. As the dewpoint rises above 70 degrees Fahrenheit (F), the air begins to feel uncomfortably muggy. When it is above 75 degrees F, the air feels very unpleasant, and above 80 degrees F it is considered to be hazardous. This is because the air is so moist that when humans sweat, the sweat is not able to evaporate and cool their bodies effectively. This can lead to heat stroke, or serious overheating.
Weather forecasting should take into account your local geography. If you live near a lake, you may have more rain if you live on the eastern shore than if you live on the western shore (remember, most weather in this country moves from west to east because of the jet stream).

As the air currents move over the lake, they pick up moisture. When the dewpoint is reached, this moisture will drop out as rain. If you live near a big mountain, you will have drier weather if you live on the western side of the mountain. As the air travels up and over the mountain, it is cooled and tends to drop precipitation in a "rain shadow" on the other side of the mountain.
A rain shadow exists where mountains get in the way of the flow of moist air. In the case of the Olympic Peninsula in Washington state, moist air masses blow in across the Pacific Ocean, and hit the 7,000 foot high Olympic mountain range. As the air is pushed up the mountains, much of the moisture drops out, and by the time the air has reached the top of the mountains it is fairly dry. This translates into an average yearly ranifall of up to 200 inches on the western side of the Olympics, and only 16 inches on the eastern side, in the "rain shadow."

2. Draw a picture of what happens as rain clouds move up and over a mountain range. Is there a rain shadow effect in your area?

No, there aren’t mountains high enough.

There are several different types of clouds, and each usually can tell you what kind of weather is coming.
Cirrus clouds are thin, wispy clouds that are high in the sky. The word cirrus is Latin for "curl of hair," which is what these clouds call to mind. They generally "point" in the direction that the wind is blowing. Cirrus clouds are usually made up of ice crystals, because they are high in the sky where it is very cold. These clouds usually mean that there will be fair weather, unless the winds are blowing from the northeast or east towards the south. Then there will be rain by the next day.
Cumulus clouds are also called "fair weather clouds." This word means "heap" in Latin, which is what they look like! They form from rising currents of warm air, and build up to great heights. These are the big, puffy clouds with big clear patches of sky in between them. Cumulus clouds usually have a flat base. They don't usually bring rain, but in the spring and summer they can turn into cumulonimbus (nimbus means "rain"), or thunderstorm clouds.
Stratus clouds are the low, gray clouds that cover the whole sky. This word means "layer" in Latin. They usually mean that rain is coming, and a dreary time is ahead. Fog is a stratus cloud on the ground.

3. The Cloud in a Bottle.
(Authored by Michael Kneese, Snake River Jr. High, Idaho.)
This activity will demonstrate the direct effects of pressure and temperature on cloud formation. Materials needed:
Wide-mouth gallon pickle jar
Heavy duty clear plastic bag
Rubber bands or masking tape
d. Place about 20 ml of water in the pickle jar.
e. With adult supervision, place a lit match into the jar.
f. Quickly place the plastic bag over the mouth of the jar, and secure a firm seal by placing the rubber band or masking tape around the top of the jar.
g. Push the bag into the jar quickly, then pull the bag out.
h. OBSERVE!

We need a match.

This activity shows how humidity, temperature and air pressure influence the formation of clouds. The water produces high humidity in the jar, and the smoke from the match provides nuclei on which the water can condense.
As the bag is pushed into the jar, pressure and temperature in the jar increases, causing the jar to clear. When the bag is pulled out of the jar, pressure and temperature decreases, allowing the water vapor to condense. This produces a "cloud" inside the jar.

4. Either go outside or look out of the window. Notice what types of clouds there are in the sky, and make a prediction about the weather. Write down your prediction and the cloud type(s). Tomorrow, write down whether or not your prediction was correct.

There are Cirrus clouds out, and even without them I can tell it’s going to be sunny tomorrow.
I was right!

One of the most common and beautiful weather events is the thunderstorm. Many stories and legends have sprung up around these storms. The Greeks thought that Zeus, their king of gods, shot lightning bolts from the sky. The Vikings believed that Thor, the god of weather, made thunder and lightning by hitting his golden hammer against a metal anvil. Native American legends told of the mighty thunderbirds that flapped their wings causing the thunder, while their flashing feathers were the lightning.

"Thunder is good, thunder is impressive; but it is the lightning that does the work." Mark Twain wrote this in a letter to a friend back in 1908, and scientists have found it to be true. Lightning originates 15,000 to 20,000 feet above sea level in the turbulent winds inside cumulonimbus clouds. Ice crystals and water droplets bump into each other, and scientists believe that this process builds up electrical charges. The positive and negative charges separate from each other, with the positive charges in the middle and upper area, and the negative charges in the lower part of the cloud. Positive electrical charges are also building up down on the ground. When the charges get big enough, the negative charges flow down to the ground, and the positive charges on the ground leap up to meet them. This lights up the negative charges into a jagged flash of light, or bolt of lightning. This all happens within a millionth of a second, which creates the optical illusion that the lightning is coming down, while in reality it is moving up from the ground.

So, how does the lightning "do all of the work?" Since the lightning bolt is so very hot, 30,000 to 50,000 degrees F, it heats the surrounding air so quickly that it expands in an instant. This creates a shock wave that we hear as an explosion of sound, or thunder. Our ears tell us that lightning comes first, and then the thunder follows. Actually, they happen at the same time, but sound travels slower than light.

Lightning can be very dangerous, killing an average of 73 people per year in the United States, and injuring about 300 people per year. In most cases, if you can hear the thunder, then it is no longer safe to be outside. The safest place to be is inside a building with plumbing or wiring extending to the ground, or inside of a vehicle with all of the windows rolled up. During a lightning storm, do not use the telephone, stay away from windows and televisions, and do not take a bath or do the dishes! Relax and enjoy the show from a safe distance.

Mark Twain also said, "We all grumble about the weather... but nothing is done about it!" The truth is that some of our actions do have an impact on the weather. Pollution can affect weather, as can forest fires. Some fires are so big and smoky that they block out the sun for extended periods of time. Clouds form when water condenses around microscopic particles like dust, smoke, or salt crystals. Scientists have discovered that if they add nuclei in the form of salt crystals or ice crystals, they can get more rain to fall from existing clouds. This is called "cloud seeding." Smoke and pollution can act to "seed" clouds as well.

Once the dewpoint has been reached and rain begins to fall, how does it turn into sleet and hail? Rain falls through layers of air as it moves towards the ground. If it falls though a layer of cold air, it may freeze and become sleet.

If these frozen drops rise and fall through warm and cold layers of air, they will turn into hail. Some hailstones can be as big as golf balls before they finally fall to Earth.
There are other awe-inspiring weather events, such as the tornado, the hurricane, and the blizzard.

Tornadoes basically "spin out" of a thunderstorm. They require warm air that can rise quickly, moisture in the lower to mid-atmosphere to form clouds and rain, and an updraft. Fronts, sea breezes and mountains can lift air. The strongest thunderstorms, which can lead to tornadoes, form under areas where the jet stream is speeding, pulling air upwards, and increasing the violence of the storm.
A tornado looks like a funnel-shaped cloud. It comes down to the ground and picks up dirt and debris. This is what gives the tornado its color. In areas with dark soil, the tornado looks black or brown. In areas with red soil, the tornado can appear reddish.
The United States has the most tornadoes of any country in the world! There are about 1,000 tornadoes in the U.S. every year. They mostly occur over the Great Plains, which has become known as "Tornado Alley." However, tornadoes have occurred in every state at one time or another. It is a good idea to know what to do in case of a tornado!

5. Read more about tornadoes, and make up a list of what to do in case of a tornado. Write a paragraph about a tornado that has happened in your state.

CA has had none! California is a very dull state in weather.

6. Go to this website, and follow the directions for creating your own tornado. Have you ever seen a tornado, or heard about one on the news?

Sorry, I have my own. A moterized... thing spins around, causing the water inside the tube to spin in a tornado-like fashion.

Hurricanes start out as thunderstorms over the ocean in the Tropics. They form between August and November, when the sea and air are at their hottest. As the storm picks up speed (pulled by the rotation of the Earth), it takes on a spiral shape. These storms are called by different names as their wind speed increases. When the wind speeds are up to 39 miles per hour, it is a "tropical depression." From 40 to 73 miles per hour, it is a "tropical storm." From 74 miles per hour on up, the storm is classified as a hurricane. These storms can be 300-600 miles wide. There are about seven hurricanes every year in the North Atlantic Ocean, and we give them names.
Why do we name hurricanes? These storms are named to make it easier for meteorologists to talk about them while they are happening. Since there may be more than one hurricane happening at the same time, trackers needed a way to keep them separate, while letting people know about watches and warnings. The first person to name a tropical cyclone (hurricane to you and me) was a forecaster in Australia. He named these storms after political figures that he didn't like. This way he could say that the politician was "causing great distress," or "wandering aimlessly about the Pacific." After that, Army and Navy meteorologists named tropical cyclones after their wives or girlfriends. This was an informal method, and in the late 1970s this system was replaced by a list that included both women's and men's names. In the Northwest Pacific, a new list is being used that consists mainly of names of flowers, birds, trees and even foods.

7. Go to the list of hurricane names. Do you find your name, or the name of someone that you know on the list? Make your own list of 10 possible names for hurricanes, using something other than personal names.

Xena
Matt
Bast
Cablen
Amen
Kathl
Lotila
Chark
Zillah
Elan

What is the difference between a tornado and a hurricane? They are both large, rotating storms, and start out as thunderstorms. That is where the similarity ends, however! Hurricanes form only above tropical seas, because they must have warm, moist air to keep them going. This is why hurricanes die out over land. Tornadoes, on the other hand, form over land, and become actual tornadoes only when they touch down. Hurricanes can be hundreds of miles wide, and last for up to nine days.
Tornadoes are much more restricted in their path (a few feet to a mile wide), and they last from a few seconds to an hour. Hurricanes raise the sea level by several feet, making water and waves the most dangerous thing about hurricanes. Tornadoes produce much more powerful winds, making debris thrown like missiles the most dangerous thing about tornadoes. Also, you can see the funnel-shaped tornado from the ground. A hurricane's swirling shape can only be seen from above, or in space.

Another amazing force of nature is the blizzard. Strictly defined, this is a snowstorm with winds of at least 35 miles per hour, and temperatures of 20 degrees Fahrenheit or lower. Where did the word "blizzard" come from? No one is quite sure, but it was used in writings by Davy Crockett back in 1830. He was describing being struck many times by violent punches as "being blizzarded." Later, in 1870 in Iowa, a newspaper used blizzard to describe a big snowstorm, and the term was in wide usage ten years later during the Blizzard of 1880.
These storms in winter can bring snow, sleet, freezing rain, and ordinary rain. These can all fall in the same place during the same storm! This happens when warm, moist air moves in over an established cold air mass. As the warm air rises up over the cold air, the moisture condenses and falls, freezing as it passes through the cold air layer. Sometimes there is a layer of colder air above that warm air, and precipitation can start as snow, melt to rain, and then re-freeze into sleet as it passes through the layers or air.

There have been many blizzards in the United States over the years, and as our weather forecasting improves, there are fewer lives lost from them. These storms do not hit us unawares anymore, as they did back in the 1800s. On Saturday, March 10, 1888, a great blizzard prevented Mark Twain's wife from joining him in New York City. He wrote: "And so, after all my labor and persuasion to get you to at last promise to take a week's holiday and go off with me on a lark, this is what Providence has gone and done about it. It does seem to me the oddest thing - the way Providence manages. A mere simple request to you to stay at home would have been entirely sufficient; but no, that is not big enough, picturesque enough - a blizzard's the idea; pour down all the snow in stock, turn loose all the winds, bring a whole continent to a stand-still: that is Providence's idea of the correct way to trump a person's trick. If I had known it was going to make all this trouble and cost all these millions, I never would have said anything about your going. Now in the light of this revelation of the methods of Providence, consider Noah's flood - I wish I knew the real reason for playing that cataclysm on the public: likely enough, somebody who liked dry weather wanted to take a walk. That is probably the whole thing - and nothing more to it."- Letter to Livy, 3/10/1888

8. Look up the blizzards that have happened in the United States over the last 100 years. Interview your parents or grandparents and find out if they remember any of these storms. Do you remember any recent blizzards? Write a paragraph about what you remember, and how it compares to the adult's memory.

No way! It dosen’t even snow here!

But there was the “Great Depression Blizzard” of New York.




TEST

1. Who made the first weather forecast?
Robert Fitzroy, in 1861

2. Where does weather "happen?"
In the toposphere.

3. What two factors make our weather?
Three: sun, water and wind.

4. What is a big area of air called?
An air mass

5. What is an air mass called if it forms over:

a. land?
A sheet
b. water?
A hurricane
c. the equator?
A tropical storm
d. Canada?
The Jet Stream

6. What happens when air masses collide?
They create thunderstorms

7. Why does weather in the United States move from west to east?
Because of the Jet Stream

8. Why is the temperature scale that we use called the Fahrenheit scale?
Because, Professor Fahrenheit invented it

9. What are some other tools that meteorologists use to forecast the weather?
Barometer, Hydrometer, Weather Vane, and a Thermometer

10. Explain how a barometer works.
It is tightly sealed, and when the pressure outside is more than the inside, the water inside floats.

11. Does wind chill make it colder outside?
Yes

12. Explain how clouds form.
Water is heated by the sun, evaporates, and collides with wind; the drops form in midair, and become a cloud

13. What is a rain shadow?
One side of the mountain block clouds from reaching the other.

14. List the cloud types, and what weather they signify.
Cirrus and Cumulus clouds both signify good weather. Cirrus clouds are thin, wispy, and made of ice.
Cumulus clouds are light, fluffy clouds, like the ones we have in our heads. They are also the most common clouds.
Stratus clouds cover the entire sky, and warn of rain.
Cumulonimbus clouds are thunderclouds. If you see one, it’s probably going to rain in… a max of 30 minutes.

15. Why do we see lightning first, and hear the thunder later, when they happen at the same time?
Sound travels much slower than light.

16. How fast does the wind have to be blowing to be called a hurricane?
74 MPH

17. What defines a blizzard?
It’s a VERY large ice storm that is VERY cold and can sometimes be VERY fatal.