What is Weather?

Key Words Weather, p. 36 Front, p. 45 Humidity, p. 38 Tornado, p. 48 Relative Humidity, p. 38 Hurrricane, p. 50 Dew Point, p. 39 Blizzard, p. 51 Fog, p. 41 Meteorologist, p. 52 Precipitation, p. 42 Station Model, p. 53 Air Mass, p. 44 Isotherm, p. 53 Isobar, p. 53

Big Ideas Chapter Goals I will explain how solar heating and water vapor in the atmosphere affect weather.  I will discuss how clouds are form and how they are classified.  I will describe how rain, hail, sleet, and snow develop.

What do you think? What is Weather? Is there a difference between weather and climate? What is temperature? What causes wind? Why does a cold drink develop water on the outside of its container?

Weather is the state of the atmosphere at a specific time and place. Includes such conditions as air pressure, wind, temperature, and moisture in the air.

What is that coming off of his head. It looks like his HEAD IS ON FIRE What is that coming off of his head? It looks like his HEAD IS ON FIRE!!! that can't be right! The Sun's heat evaporates water into the atmosphere forming clouds and returning the water to Earth as rain or snow; the Sun also heats air. See if you can explain the picture using your knowledge of physical changes. Hint: Chris Zorich was a Chicago Bear. This week he was in Green Bay. Football in Wisconsin is COLD...dare I say freezing cold)

Temperature is a measure of air molecule movement. a. The Sun's energy causes air molecules to move rapidly; temperatures are high and it feels warm. b. When less of the Sun's energy reaches air molecules, they move less rapidly and it feels cold.

"Boiling" does not mean hot. It can feel hot to us sometimes, (like with water) but what would you say about liquid Nitrogen boiling at -198 degrees Celsius? It bubbles but would freeze off your hand! Boiling is heating a liquid to a gas.

"Freezing" does not mean cold. It can feel cold to us sometimes, (like with ice) but what would you say about a solid cookie sheet that has been at 200 degrees C for 8 minutes? An Aluminum pan wouldn't melt until 660 degrees C. It BURNS but is still frozen solid.

4. Wind—air moving in a specific direction a. As the Sun heats air, it expands, becomes less dense, rises, and has low atmospheric pressure.

b. Cooler air is denser and sinks, causing high atmospheric pressure. c. Air moves from high pressure areas to low pressure areas, causing wind.

Differences in pressure from one area to another causes air to move about quickly in an attempt to equal out the different pressures. This rushing of air is what we know as wind. Pressure differences also creates differences in temperature.

5. Humidity—the amount of water vapor in the air 5. Humidity—the amount of water vapor in the air. The more water that is in the air there is, the higher we say that the humidity has risen.

a. Warmer air can hold more water vapor, tending to make it more humid. Humidity can be measured in a number of ways. Relative humidity compares how much water is in the air, with how much could be in the air.

b. Relative humidity—the amount of water vapor in the air compared to what it can hold at a specific temperature How does the temperature Of air influence the amount of Water vapor?

c. When air cools, it can't hold as much water vapor, so the water vapor condenses to a liquid or forms ice crystals.

d. Dew point—the temperature at which air is saturated and condensation forms

The dew point varies from day to day, and from location to location, and depends on both the temperature, and on the amount of water in the air.

Clouds form as warm air is forced upward and cools Clouds form as warm air is forced upward and cools. Then the water vapor condenses in tiny droplets that remain suspended in the air. The shape and height of clouds vary with temperature, pressure and the water vapor in the atmosphere.

When air is cooled to its dew point near the ground, it forms a stratus cloud called fog.

At any given moment, about one half of the surface of the Earth is surrounded by a cover of clouds.

B. Shape a. Stratus—smooth, even sheets or layers at low altitudes

b. Cumulus—puffy, white clouds, often with flat bases

c. Cirrus—high, thin, white, feathery clouds made of ice crystals

3. Height a. Cirro—high clouds b. Alto—middle-elevation clouds c. Strato—low clouds

4. Nimbus clouds are dark and so full of water that sunlight can't penetrate them.

C. Precipitation—water falling from clouds When water droplets in clouds combine and grow large enough precipitation falls to Earth Air temperature determines whether the droplets form rain, snow, sleet, or hail.