1. Weather and The Water Cycle

2. Weather = the condition of the atmosphere at a specific time and place.
Meteorology = the study of the atmosphere and weather, including measurements of temperature, air pressure, wind speed wind direction, and the amount of moisture in the air.
Weather is studied and predicted by meteorologists.

3. Weather systems generally move WEST TO EAST across the United States.
Why?
The Coriolis Effect
and convection currents
…we’ll learn more about this later.

4. WEATHER TOOLS & TECHNOLOGY.
-Weather forecasting is an attempt to make predictions about future weather
-Short-range forecasting is easier than long-range.
Weather maps help make predictions by showing precipitation, wind direction, temperature, cloud cover, air pressure, and fronts.

5. WEATHER TOOLS & TECHNOLOGY.
Technology has helped make weather forecasting easier and more accurate.
Weather data is taken at thousands of locations, gathered instantly, and applied to weather prediction models.

6. Weather Questions:
To understand the weather, meteorologists must know:
1) How the atmosphere heats and cools.
2) How clouds form and produce rain.
3) What makes the wind blow.

7. How do clouds form and produce rain? THE WATER CYCLE
Evaporation: Heat (energy) is absorbed by liquid water at the surface of the earth and changes into water vapor (gas).
- Most evaporation comes from the ocean.

8. THE WATER CYCLE
Transpiration: water is released into the atmosphere as water vapor through small pores in plant leaves.

9. THE WATER CYCLE
Condensation: water vapor in the atmosphere cools and is converted to liquid water.
- Clouds
- Fog
- Dew
- Condensation on bottles, windows, etc.

10. Dew Point & Condensation
Dew Point: the temperature at which condensation occurs.
- Cooler temperatures are needed for condensation.
- Particles are needed for water vapor to condense on.

11. Then, Precipitation!
Precipitation: water released from clouds in the form of rain, drizzle, snow, sleet, or hail.
- Occurs when the water droplets get big enough to overcome gravity; cloud has become “over-saturated.”

12. What about hail?
Not all clouds produce precipitation, but some produce round blocks of ice called HAIL.
Hail starts as an ice pellet inside a cold region of a cumulonimbus cloud.
Gets pushed up by strong updrafts to the cold region many times, forming a new layer of ice around it every time (layered like an onion.)
Eventually heavy enough to fall to the ground.

13. Surface Runoff
= the flow of water that occurs when excess storm water, meltwater, or other sources flows over the earth's surface
- May carry pollutants or cause erosion.

14. Groundwater & Aquifers
Groundwater is the water found underground in the cracks and spaces in soil, sand and rock.
It is stored in geologic formations of soil, sand and rocks called aquifers.

15. Groundwater & Aquifers
Groundwater supplies are refilled by precipitation that seeps through the cracks beneath the land's surface.
People may face serious water shortages because groundwater is used faster than it is naturally refilled, or because groundwater is polluted by human activities.

16. Relative Humidity
Remember, humidity is the amount of water vapor in the air.
Relative humidity: the amount of water vapor the air is holding compared to the amount of water vapor the air can hold at that temperature.
Remember, warm air can hold more water vapor than cold air.

17. Why is the water cycle important?
-The water cycle is critical not only to weather, but to life on earth.  Rain is necessary for the survival of plants and humans. 
-Condensation is necessary for cloud formation. 
-Evaporation is necessary to cooling and keeping a good balance of water vapor in the air.

18. Why is the water cycle important?
-It influences the intensity of climate variability and change, and is the key feature of drought and floods. -Its abundance and timely delivery are critical for society and the environment.