Weather

1. Weather Section 1: Water in the Atmosphere

2. Basics • The Water Cycle is the movement of water between the atmosphere and earth’s surface • Evaporation: Process where liquid water turns to a vapor • Condensation is when water vapor changes back to a liquid (#6) • Dew Point: Is the temp where condensation happens (#7)

3. Humidity • The measure of the water vapor in the air • Air can hold various amounts at different temperatures • Relative Humidity: is a percentage…it tells how much is in the air in relation to what it can actually hold. • Psychrometers: are instruments used to measure relative humidity • Measures based on the temperature change in the wet bulb of the psychrometer.

4. Clouds • Cirrus Clouds: • Soft, feathery • Form at high levels in low temperatures • Made of ice crystals • Cumulous Clouds: • Fluffy like cotton balls • Lower to the ground but can extend higher • Can be combined with the suffix –Nimbus to indicate a rain cloud

5. Stratus Clouds: • Form in flat layers and cover most of the sky • Can produce rain or snow (nimbostratus)

6. Other Clouds • The Prefix “—Alto” may be added to a cloud if it is one of the three main types, but higher than usual • Examples: altocumulus, altostratus • Fog is formed when hot, humid days lead to cooler nights, causing vapor to condense lower to the ground. • Fog tends to form over areas with more water…

7. Pg. 439 Section 2: Precipitation

8. Precipitation • Any form of water that leaves clouds and comes back to Earth’s surface • Does Precipitation always fall from clouds? • No • Remember: precipitation occurs when ice or liquid is heavy enough to fall • Types of Precipitation: Rain, Hail, Snow, Sleet, Freezing Rain

9. Rain • Precipitation that falls as drops of water • Small drops are called Drizzle or mist • These usually come from stratus clouds

10. Hail • Round pellets of ice (larger than 5mm---about the size of a pea) called hailstones • Updrafts of wind carry the ice pellet through the cloud many times, forming many layers of ice • Hail tends to have rings when cut in half (like an onion)

11. Snow • Water in the clouds is changed strait to ice crystals—ie. Snowflakes • Powder happens when snow falls in cool, dry air • Clumpy snow happens in moist, humid areas.

12. Sleet • Raindrops freeze after leaving the cloud • Sleet is usually smaller than 5mm (the size of a pea)

13. Freezing Rain • Rain that freezes when it touches a cold surface • Causes ice to build up and coat things at the surface level

14. Pg. 442 Air Masses & Fronts

15. Air Masses • A huge body of air that has it’s own temperature, humidity, and air pressure. • Can spread over millions of kilometers and be up to 10 kilometers deep • Characterized by temperature and humidity • 4 kinds(North America): Tropical, Polar, Maritime, and Continental.

16. Tropical • Warm air masses that form in the tropics • Have low air pressure

17. Polar • Cold air masses that form in polar regions • High air pressure

18. Maritime • Form over oceans • Can become very humid

19. Continental • Air masses that form over land • Drier than maritime because they don’t have the evaporation process.

20. Combining Air Masses • Types of air mass can be combined to imply area of Earth and the part of the Earth it forms over • Example: • Maritime Tropical---Forms over tropical oceans • Maritime Polar---Form over polar ocean areas • Continental Tropical---Form over tropical Land • Continental Polar---form over polar land areas

21. Air Mass Movement • Moving air masses interact with other masses causing the weather to change • Prevailing Westerlies: Major wind belts of US • Push Air masses west to east • Jet Streams: Bands of high speed winds 10 kilometers from the surface of Earth

22. Fronts: Huge masses of air that move across oceans and collide • Don’t’ mix well due to different densities • Area of the collision develops a “Front” • 4 types---type of front depends on the characteristics of the air masses and how they are moving.

23. Fronts • Cold: • Cold air (dense) sinks…Warm air (less dense) rises • Cold air mass slides under warm air mass, pushing the warm air up • As it rises, it expands and cools, making vapor change rapidly to water or ice crystals…forming clouds • Can move quickly and cause thunderstorms…brings colder, drier air and lower temperatures.

24. Warm: • Fast air mass overtakes a colder air mass • Warm air moves over the cold air • Rain or snow forms if the air is humid…clouds if the air is dry • Warm fronts move slow, lasting several days…. • After---weather is warm and humid

25. Stationary: • Warm and cold meet, but neither move the other • Water vapor can condense along the front causing rain, snow, fog, or clouds for days. • Occluded: • Warm air mass trapped between two cold air masses • Cold is denser, so they go under the warm and push it upward • Temperature near the ground becomes cooler • As warm air cools, weather becomes rainy.

26. Read pg. 448… • Complete the double bubble map for cyclones and anticyclones • Complete 2c pg. 449

27. Pg. 450 Section 4: Storms

28. Storm • A violent disturbance in the atmosphere • 4 types: Thunderstorms, Tornadoes, Snow Storms, Hurricanes

29. Thunderstorms • A small storm that often has heavy rain and frequent thunder/lightning • Form in Cumulonimbus clouds (thunderheads) • Thunderstorms form on hot, humid afternoons when warm air is forced upward along a cold front (warm air rises rapidly) • Lighting is a sudden spark, or electric discharge that happens when charges jump.

30. Tornadoes • A rapidly whirling, funnel-shaped cloud that reaches down from a storm cloud to touch Earth’s surface • Over a lake or ocean, it is called a waterspout. • Formation: • Commonly—in thick cumulonimbus clouds • When thunderstorms are likely • Warm air mass and cold air mass meet going opposite directions

31. Snow Storms • Occurs mostly in Northern US and at higher elevations • Large amount of precipitation is snow • Heavy snow can block roads • Can be extremely dangerous if wind picks up, blowing the snow and hindering visibility

32. Hurricanes • A tropical cyclone that has winds of 119 kilometers per hour or higher • Begins over warm ocean water as a low pressure area or tropical disturbance. • Grows into a tropica storm, then a hurricane The hurricane gets its energy from the warm, humid water creating bands of wind and heavy rain.