1. Chapter 5 Weather

2. 5.1 A. What is weather? The state of the atmosphere at a specific time and place.

3. B. Weather Factors 1. Air Temperature -the higher the temperature, the faster the air molecules are moving

4. 2. Wind a) air moves from regions of high pressure to regions of low pressure a. warm air- less dense- low pressure b. cool air - more dense- high pressure b) wind speed is measured with an anemometer

5. c) wind direction Wind vane -points to the direction from which the wind came Wind sock -points in the direction the wind is blowing

6. 3.Humidity -amount of water vapor in the air  Warm Air More water vapor present Water molecules move quickly and don’t come together  Cool Air Less water vapor present Water molecules move slowly and stick together to form condensation When air is saturated, precipitation occurs

7. 4. Relative Humidity  The amount of water vapor present in the air compared to amount needed for saturation at a specific temperature  This measurement is given as a percent (think of it as how much water is in a sponge)

8. 5. Dew Point  The temperature at which air is saturated with water vapor and condensation forms  This temp. changes with the amount of water vapor in the air  P.121 (figure 4)

9. C. Clouds 5 Steps of Cloud Formation: 1. Warm air forced upward, expands, cools 2. Relative humidity increases 3. When R.H. reaches 100%, air is saturated 4. Water vapor condenses around small particles such as dust and salt 5. Billions of these droplets form a cloud

10. Cloud Classification  SHAPE Stratus- low altitude, fair weather, rain or snow Cumulus- puffy, white, tall, fair weather, thunderstorms Cirrus- high, thin, feathery, white, fair weather, indicates approaching storms  HEIGHT Cirro- high clouds Alto- middle clouds Strato- low clouds Dark Clouds- “nimbo”

11. D. Precipitation A. Water droplets combine and grow large enough to fall to Earth B. Forms: 1. Rain- temp. above freezing 2. Snow- temp. below freezing 3. Sleet- raindrops freeze near surface 4. Hail- windy conditions, ice pellets

12. 5.2 Weather Changes A. Air masses -develop over land with similar properties -changes occur when air masses move -four different air masses over the U.S. 1. Cold DryCanada, Northern Plains 2. Hot DryMexico, Texas 3. Cool MoistWashington, New England 4. Warm MoistS. California, Florida

13. B. Winds 1) cyclones -winds blow in a counter-clockwise direction -stormy weather 2) anti-cyclones -winds blow in a clockwise direction -fair weather

14. C. Air Pressure -measured with a barometer -low pressure = cloudy weather -high pressure = fair weather

15. D.Fronts- boundaries between air masses Cold Front Cold air wedges under warm air pushing it up Thunderstorms and tornadoes Warm Front Air advances over heavier, cooler air Hours and days of wet weather Occluded Front Colder air sandwiches warm air showers Stationary Front No advancing air Light wind and precipitation

16. E. Severe Weather 1. Thunderstorms -warm -moist air masses and along fronts -rain -hail -strong wind -lightning -flash flooding

18. 2. Blizzards -snow fall -low temps -more than 3 hours -visibility less than 400 meters -wind more than 56 km/hr

20. 3. Hurricanes -low pressure system -turn heat from ocean to wind -at least 119 km/hr Atlantic Ocean- Hurricanes Pacific Ocean- Typhoons Indian Ocean- Cyclones

22. 4. Tornadoes -winds blow at different heights -winds blow in different directions -winds blow at different speeds (wind shear) -rotating column parallel to the ground -funnel cloud forms when an updraft tilts the column of rotating air -Fujita Scale ranks the severity of the storm

24. 5.3 Weather Forecasts

25. -Meteorologist -person who studies the weather -gathers information on current weather -predicts future weather

26. A. Measurements - temperature -air pressure -humidity -precipitation -winds

27. B. Instruments Common -thermometer- temp. -rain gauge- rainfall -anemometer- wind speed -barometer- air pressure -psychrometer- humidity -wind vane- wind direction Modern -satellites -computers -Dopplar Radar

28. C. Weather Maps Air Pressure a) High pressure = good weather = b) Low pressure = poor weather = H L

29. Isobars a. lines connecting points of equal atmospheric pressure b. lines close together: -large pressure difference over a small area -results in strong winds Isotherms -lines connecting points of equal temperature

30. Weather Station Model -describes the weather at one location