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Why Fog Pools in Valleys at Dawn

5th grade nonfiction passage about valley fog: 199 words, six questions, an answer key and vocabulary.

5th grade nonfiction valley fog 199 words

Why Fog Pools in Valleys at Dawn

On a calm, clear morning, people who live in hills often see a strange sight. The valley floor is filled with a thick white fog, like milk in a bowl, while the hilltops above it shine in the sun. The fog is no accident. It follows from how air behaves after dark.

When the sky is clear at night, the ground loses its heat and cools off. The air touching the ground cools too. Cold air is heavier than warm air, so on a slope it slowly slides downhill, much like water would, and collects in the lowest places. Valleys end up as pools of the coldest air.

Air always holds some water vapor, but cold air can hold less of it. When the air in the valley gets cold enough, the vapor can no longer stay invisible. It turns into countless tiny drops floating close to the ground. That cloud at ground level is fog.

Fog like this lasts only until the morning sun warms the ground. As the air heats up, the drops change back into vapor, and the fog thins and vanishes. Drivers are told to slow down in fog, because they cannot see far ahead.

Questions

  1. What does the valley fog look like from the hilltops? in the text

  2. Why does cold air slide downhill into valleys? in the text

  3. What happens to water vapor when the valley air gets cold enough? in the text

  4. Why are valley floors foggier than hilltops? think about it

  5. What makes the fog thin and vanish in the morning? in the text

  6. Why are drivers told to slow down in fog? think about it

Words to know

fog
a cloud of tiny water drops near the ground
valley
low land between hills or mountains
slope
the slanted side of a hill
vapor
water in the form of a gas in the air
vanishes
disappears completely
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One passage, three levels

The same topic and facts written three ways, so a mixed class can read and talk about one text. Each group’s sheet shows only a shape; the key says which is which.

● Easier · 181 words · Flesch-Kincaid grade 2.5

On a calm, clear morning, people in the hills may see a strange sight. The valley is full of thick white fog, like milk in a bowl. The hilltops above it shine in the sun. This is not an accident. It comes from how air acts at night.

When the sky is clear at night, the ground loses its heat and gets cold. The air touching the ground gets cold, too. Cold air is heavier than warm air. On a slope, it slides downhill, much like water would, and collects in the lowest places. So valleys get pools of the coldest air.

Air always holds some water vapor. But cold air can hold less. When the valley air gets cold enough, the vapor can not stay hidden. It turns into countless tiny drops near the ground. That cloud at ground level is fog.

Fog like this lasts until the morning sun warms the ground. The air heats up, the drops turn back into vapor, and the fog fades away. Drivers must slow down in fog, because they can not see far.

▲ This passage · 199 words · Flesch-Kincaid grade 4.4

On a calm, clear morning, people who live in hills often see a strange sight. The valley floor is filled with a thick white fog, like milk in a bowl, while the hilltops above it shine in the sun. The fog is no accident. It follows from how air behaves after dark.

When the sky is clear at night, the ground loses its heat and cools off. The air touching the ground cools too. Cold air is heavier than warm air, so on a slope it slowly slides downhill, much like water would, and collects in the lowest places. Valleys end up as pools of the coldest air.

Air always holds some water vapor, but cold air can hold less of it. When the air in the valley gets cold enough, the vapor can no longer stay invisible. It turns into countless tiny drops floating close to the ground. That cloud at ground level is fog.

Fog like this lasts only until the morning sun warms the ground. As the air heats up, the drops change back into vapor, and the fog thins and vanishes. Drivers are told to slow down in fog, because they cannot see far ahead.

■ Harder · 207 words · Flesch-Kincaid grade 7.5

On a still, cloudless morning, residents of hilly country are frequently treated to a remarkable spectacle. The floor of the valley is brimming with dense white fog, resembling milk in a bowl, while the summits above it glow in the sunshine. This scene is no coincidence. It follows directly from the way air behaves after nightfall.

When the sky is clear overnight, the ground radiates its heat away and grows cold, and the air in contact with the ground cools as well. Cold air is heavier than warm air, so on a slope it gradually flows downhill, much as water would, and gathers in the lowest places. Valleys therefore become reservoirs of the coldest air.

Air always contains some water vapor, but cold air is capable of holding less. When the air in the valley becomes sufficiently cold, the vapor can no longer remain invisible. It condenses into countless minuscule droplets suspended near the ground. This cloud at ground level is fog.

Fog of this kind persists only until the morning sun warms the ground. As the air heats up, the droplets revert to vapor, and the fog thins and disappears. Drivers are advised to slow down in fog, because they are unable to see far ahead.

Download as one PDF

How to use it

  1. Press Read it big (or B) to put the text on the projector, or Full screen (F) to fill the whole screen.
  2. Ask the questions one at a time and use Show answer when the class has decided. A shows or hides every answer.
  3. Print student copy for the class, or Print with answers for yourself.

Ideas for class

  • Before reading, put fog, valley, slope, vapor and vanishes on the board with their meanings from the Words to know section and have students predict what the text will be about.
  • Read it aloud once while students follow along, then have them reread it alone or with a partner. At a calm 100 words a minute it takes about 2 minutes to read aloud.
  • Use the Read it big button (or B) to put the text on the projector, and Show answer on one question at a time so the class commits to an answer first.
  • Question 4 asks the reader to infer. Ask students to point to the words in the passage that led them to their answer.
  • Ask students to write one question the passage did not answer, then look for the answer in a book or on a classroom screen.
  • Print the student copy for independent work and keep the answer-key copy for yourself.

Related

Questions

What reading level is "Why Fog Pools in Valleys at Dawn"?

It was written for 5th grade. It has 199 words and works out to a Flesch-Kincaid grade level of about 4.3. That is a formula's estimate from sentence length and syllables, and it is not a Lexile or a guided reading level, so check it against your students.

What do the questions ask?

There are six. 4 ask for something the text says directly and 2 ask the reader to work something out from clues. Each has an answer in the key, and the answers are written as a teacher would accept them, not as the only possible wording.

How long does it take to read?

About 2 minutes read aloud at 100 words a minute. For a one-minute fluency check, paste it into the fluency timer and use the word count.

Can I print it?

Yes. Print student copy gives the passage, the questions with lines to write on, and the word meanings. Print with answers gives the same page with the answers filled in. Both are made in your browser.

Is this passage from a published book?

No. It was written for Peabody Teach, so there is no book to buy and no login to read it.

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