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What is Weather?

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Sarah Chrzanowski

on 31 January 2017

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Transcript of What is Weather?

What is Weather?
is the state of the atmosphere at a specific time and place.

What is the weather in South Lyon right now?
Weather Factor:
Air Temperature
Air is made of moving molecules.

is a measure of the average amount of motion of molecules:

- When the temperature is high, air molecules move rapidly ...it feels warm!

- When the temperature is low, air molecules move more slowly...it feels cold!
Weather Factors:
If something is
, what does that mean?
Dense means molecules are packed closely together.

What does
high (air) pressure
High air pressure means the air molecules are packed closely together. This dense air

What does
low (air) pressure
Low air pressure means the air molecules are spread further apart. This less dense air

Warm air
expands, becomes less dense,
and rises.
Cold air
condenses, becomes
more dense, and sinks.
How does the Sun affect weather on Earth?
*The sun provides almost all of Earth's energy*
Weather Factors:
Used to
Measure Wind

- wind vane or
- wind sock

To measure WIND SPEED:
- Anemometer
What is Weather?
P. 36-43 The Air Around You
Weather Factors
Weather describes conditions/factors such as:
- air temperature
- wind
- moisture content in the air (humidity)
- air pressure
(we will explore the first three in this prezi)
1) It gives us precipitation: The Sun evaporates the water on earth, which forms clouds, and falls again as precipitation (rain or snow).

2) It heats Earth's air and water: The Sun heats the Earth's surface, which then heats the air above it.
Weather Factors:
The sun heats the earth unevenly, so you have some areas that are
colder (high pressure area)

and some areas that are
warmer (low pressure area)

Air moving from areas of
pressure of areas of

Weather Factors:
Where does water go when it evaporates?
Water vapor molecules fit into spaces between the air molecules.
: The
of water vapor held in the air.
Weather Factors:

Air does NOT always contain the same AMOUNT of water vapor.
MORE water vapor can be present in WARM air than in cold air. WHY?
When more and more water vapor molecules stick together, they will (condense) turn into water droplets.

Water vapor molecules in
air move FAST, so the molecules CANNOT easily stick together to form water droplets. So MORE water vapor can be present before it (condenses) turns into water droplets.

Water vapor molecules in
air move SLOWLY, so the molecules DO easily stick together to form water droplets. So LESS water vapor can be present before it (condenses) turns into water droplets.

Weather Factors:
Relative Humidity
If you run a sponge under a faucet, eventually it becomes so full that it CANNOT hold any more water. When the sponge cannot hold any more water, we say the sponge is SATURATED.

The air is like a sponge, and can become so
water vapor
it cannot hold any more. At this point, the air is saturated. When the air is saturated and cannot hold anymore water vapor, the water vapor (condenses) turns into water droplets.

Weather Factors:
Relative Humidity
Relative Humidity:
A measure of the amount of water vapor present in the air compared to the amount needed for saturation.

Since this comparison is a ratio, it can be turned into a PERCENT.

Example: Let's say that the air can hold 22 grams of water, but at the moment, it only has 11 grams of water. The ratio would be 11g/22g or turned into a percent it would be 50%.

We would say the relative humidity is 50%.

Weather Factors:
Dew Point
1. There is a certain amount of water vapor in the warm air during the day.

2. The temperature drops at night and the colder air can't hold all of that water vapor. (Do you remember that warm air can hold more water vapor than cold air?)

3. The air will become saturated (too full of water vapor) and the water vapor will (condense) turn into water droplets.

4. You see those water droplets on the
grass in the morning- it's called

Let’s say it’s daytime and the air temperature is 15° C. At 15° C it’s a little bit warmer and warmer air can hold more water vapor. The total amount of water vapor the air can hold at 15° C is 11 grams. However, today, there is only 8 grams of water vapor in the air. At nighttime it starts to cool down to 10° C. At 10° C the air can hold 8 grams of water vapor because cold air can’t hold as much water vapor. During the day, we had 8 grams of water vapor and that stays the same as we lead into nighttime. Since we have the same amount of water vapor as the air can hold, we have reached our saturation point. That means if we have 8 grams of water vapor and the air can only hold 8 grams of water vapor, the water vapor will start condensing into water droplets. Those water droplets are what you see in the morning on the grass as dew. So the dew point is 10° C because this is the temperature at which the water vapor condensed into water droplets.

Weather Factors:
Dew Point
Forming Clouds
Dew Point:
The temperature at which air is saturated and condensation forms.

How are clouds formed?

1. Air heats up. WARM AIR is LESS DENSE (air
molecules are further apart), so the warm air RISES.

2. It's colder the higher you go in the troposphere, so the rising air begins to cool down.

3. Cooler air cannot hold as much water vapor, so the water vapor condenses into little water droplets that form around dust and salt.

4. The water droplets are not big/heavy enough
to fall to earth, so they stay suspended
in the air. Billions of these droplets
form a cloud.
Classifying Clouds
Clouds are classified mainly by shape and height.

The shape and height of clouds vary with temperature, pressure, and the amount of water vapor in the atmosphere.

- form layers or smooth even sheets in the sky
- form at low altitudes
- associated with fair weather, rain, or snow
- puffy, white clouds with flat bases
- sometimes tower to great heights
- can be associated with fair weather or thunderstorms
- appear fibrous or curly
- high, thin, white, feather clouds made of ice crystals
- associated with fair weather, but can indicate approaching storms
- high clouds
- middle-elevation clouds
- clouds at low elevations

Many cloud names combine the cloud height and cloud shape, such as alto cumulus.

Rain or Snow Producing Clouds
- Clouds associated with rain or snow often have the word NIMBUS attached to them.

- Nimbus is latin for "dark rain cloud"

- The water content of nimbus clouds is so high that little sunlight can pass through them.

- When a cumulus cloud grows into a thunderstorm, it is called a cumulonimbus (kyew myuh loh NIHM bus) cloud. These clouds can tower to 18km.

- Nimbostratus clouds are layered clouds that can bring long, steady rain or snowfall.
: Water falling from clouds.

Precipitation occurs when cloud droplets combine and grow large enough to fall to earth.

Two reasons why some raindrops are bigger than others:

1. Updrafts- the rain begins to fall and wind swoops it back upward into the cloud where it gains more water and gets bigger before it falls to earth.

2. Evaporation- if the air is dry, the water in the raindrop evaporates as it falls to earth, causing the raindrop to get smaller.

Four main types of precipitation:

- water falling when temperature is above freezing

- the air temperature is so cold that water vapor (from the cloud) changes directly to a solid

- raindrops pass through a layer of freezing air near Earth's surface, forming ice pellets

- Hail forms in the cumulonimbus clouds of a thunderstorm. Water freezes in layers around a smaller piece of ice forming larger lumps of ice that fall to earth's surface. The small piece of ice begins to fall and the wind swoops it back upward into the cloud where it gains more water and freezes into a bigger piece of ice. The hail begins to fall again, and can be swooped up many times, getting bigger and bigger each time before it finally falls to earth. Most hail is smaller than 2.5 cm, but can grow larger than a softball! Hail produces the most damage, often breaking windows, denting cars, and harming crops.

End =)
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