1. Weather

2. Heating the Earth Weather is the daily conditions of the atmosphere
The factors that interact to cause weather are heat energy, air pressure, winds, and moisture

3. Moisture in the Air
Water vapor or moisture in the air is called humidity
Humidity can vary from place to place and time to time
Latent heat is the amount of energy that is absorbed or released during a phase change.

4. Absolute humidity
The mass of humidity contained in a certain amount of air
absolute humidity = mass of water vapor (g)
volume of air m³

5. Relative Humidity
The actual amount of water vapor in the air relative to the amount of water vapor needed to reach saturation
relative hum = amt. of H2O vapor in air X 100
amt. of H2O vapor to saturation
If the temperature does not change and more moisture enters the air, RH goes up. If the temperature decreases RH goes up. If temperature goes down RH decreases.

6. Dew Point
When the air temperature and the dew point is the same 100% humidity occurs. This causes dew on cool objects. When the temperature is below freezing frost occurs.

7. Measuring Relative Humidity
Psychrometer has two thermometers, one dry and one wet. The difference in the temperature of the two will determine
the humidity using the table.

8. Water Drop Formation
Water needs to condense on a condensation nuclei

9. Clouds: collection of water drops

10. Stratus
Low altitude sheet like clouds may produce rain (nimbostratus)

11. Cumulus
Fair weather clouds, can form cumulonimbus if troposphere is unstable

12. Cirrus
Ice crystals high in atmosphere, usually rain within 24 hours

13. Fog: Surface Clouds Radiation fog forms with nightly cooling
Advection fog forms when warm, moist air moves across a cold surface

14. Some Unusual Clouds

24. Precipitation
When water vapor in the clouds becomes too heavy, it can fall as rain, sleet, snow, or hail
Cloud droplets must first increase in size until gravity pulls them down
If they pass through extremely cold layers of air, they can freeze and produce sleet
Snow is formed when water vapor changes directly into a solid
Hail is formed when water droplets hit ice pellets

28. Causes of Precipitation
Coalescence is the formation of a large droplet by the combination of smaller droplets

29. Measuring Rainfall A rain gauge is used to measure precipitation
Snow usually is measured as 10” of snow = 1” of rain

30. Doppler Radar
The intensity of precipitation can be measured using Doppler Radar which is the bouncing of radio waves off rain or snow.

31. Weather Patterns: Air Masses
Changes in the weather are caused by very large areas of air with specific temperature and humidity called air masses
There are four main air masses that affect the weather in the United States
They are named for the regions they originate in

33. Maritime masses
Maritime tropical air mass originates near the equator over the ocean, it brings warm moist air onto the continent
Maritime polar air mass forms over the Pacific Ocean in both winter and summer, it forms over the North Atlantic and brings cold winter weather in the winter and cooler temperatures during the summer to the east coast

34. Continental masses
The continental tropical forms over land in the Southwestern US it brings dry hot air
The continental polar mass forms over the land in Canada and brings very cold dry air into the US

35. Fronts
Fronts form when large air masses meet that have different temperatures and humidity
The weather at a front is can be very unstable and stormy
There are four different types of fronts: cold front, warm front, occluded front, and stationary front

36. Cold Front
A cold front forms when a mass of cold air pushes over a mass of warm air
The cold air pushes its way below the warm air
Violent storms, even tornadoes can be associated with these front
Fair, cooler, and drier air usually follows

37. Cold Front

38. Warm Front
A warm front forms when a mass of warm air overrides a mass of cooler air
Rain showers can accompany a warm front
Hot and humid weather follows

40. Occluded Front
When a very fast moving cold air mass overtakes a slower moving warmer air mass, an occluded front forms
It produces less severe weather than a warm or cold front can

41. Stationary Front
A stationary front is formed when a cold air mass and a warm air mass meet and do not move
This produces several days of rain

43. High and Low Pressure Systems

44. High Pressure
Some high pressure systems are associated with cold air systems that move in and change the weather
Subtropical high pressure systems are slow moving, usually bring very warm conditions

45. Low Pressure Systems
Low pressure systems are associated with precipitation and a change to the weather for an extended time
Low pressure systems can bring rain or snow
Low pressure systems can bring a sudden dramatic drop in temperatures

46. Measuring Air Pressure
A barometer measures the pressure of the air
Mercury Barometer
Aneroid Barometer

47. Winds
Both local winds and global winds are caused by differences in air pressure due to unequal heating of the atmosphere
Isobars that are closer together indicate stronger winds
Winds travel from areas of high pressure to areas of low pressure

48. Measuring Wind
Wind is measured by an anemometer for speed and a weather vane for direction

49. Storms A storm is a violent disturbance in the atmosphere
It is marked by a sudden drop in pressure
Some may cover a very large area

50. Rainstorms and Snowstorms
Caused when two different fronts collide
When a warm front overrides a cold front
Rain or snow occurs
During the winter, if the rain freezes it can cause an ice storm

52. Thunderstorms Occurs when a cold front meets a warm front
Thunder and lightning form within the clouds
Dangerous down drafts and wind shears are often present

53. Lightning
Occurs because areas of positive and negative charges build up inside the storm, then a sudden discharge between two clouds or the clouds and the ground

54. Thunderstorm Safety

55. Cyclones and Anticyclones
Areas of low pressure that contain rising warm air are cyclones
Winds spin in a counterclockwise inward movement with rain and storms
Areas of high pressure, cool and dry winds are anticyclones
Winds spin in a clockwise movement from the center outward

58. Hurricanes Powerful cyclone Warm moist air begins to rise rapidly
Cooler air moves in and the air begins to spin
The pressure in the center drops and more air rushes in causing the winds to spin faster
Air forms a doughnut shape wall of strong winds with a calm center
These storms are accompanied with strong winds and a high storm surge
These are the most powerful storms on Earth

62. Tornadoes Whirling funnel shaped cloud
Develops in heavy cumulonimbus clouds
Air pressure at the bottom is low so the funnel acts like a vacuum cleaning
Occur in the spring and summer in the area called Tornado Alley

65. Forecasting the Weather
Just think the end
is near!!!!

66. Predicting the Weather
Meteorologist is a person who studies and predicts the weather
They interpret weather information from local weather observers, balloons, satellites, and weather stations around the world

67. Weather Maps
Data from stations around the country is gathered and put on weather maps
This includes temperature, air pressure, precipitation, and the wind speed and direction
Information about cloud cover, air masses, and fronts may be included
The information is recorded by a number of symbols and numbers

68. Recording Weather Data

69. Isotherms and Isobars Isotherms connect points of equal temperatures
Isobars connect points of equal pressure

70. Symbols

71. Controlling the Weather
At the present time, weather control is limited to seeding of clouds
This is done by placing dry ice or silver iodine crystals into the super cooled layers of the stratosphere
These cause large ice crystals to form that eventually fall as rain

72. I know how you feel!!!!
Nothing is wrong
with your eyes!!