2. Weather! Weather!

3. Weather – the present state of the atmosphere Caused by the interaction of air, water, and the sun Caused by the interaction of air, water, and the sun The water cycle plays a large role in this The water cycle plays a large role in this Evaporation→Condensation→Precipitation Evaporation→Condensation→Precipitation

4. The Water Cycle

5. 4 Main Factors that Determine Weather: 1. Air Pressure 2. Wind 3. Temperature 4. Humidity A Weather Balloon

6. Humidity Humidity – the amount of moisture (water vapor) in the air Humidity – the amount of moisture (water vapor) in the air Water Vapor – water in a gas Water Vapor – water in a gas state state

7. Two types of humidity 1. Specific humidity – the actual amount of water vapor in the air at a given time and place 2. Relative humidity – the measure of the amount of water vapor in the air compared to the total amount of water vapor that the air could hold a particular temperature

8. More on Relative Humidity If an air mass has 50% relative humidity this means that the air is holding 50% or half of the water vapor that it could hold at its present temperature. If an air mass has 50% relative humidity this means that the air is holding 50% or half of the water vapor that it could hold at its present temperature. Saturated air has a relative humidity of 100%. Saturated air has a relative humidity of 100%. We can measure relative humidity by using a Psychrometer. We can measure relative humidity by using a Psychrometer.

9. Dew Point – temperature at which the air is saturated and condensation takes place Question: Why don’t we typically have dew on a cloudy night? (Hint: Remember, warm air has the ability to hold more water vapor than cold air)

10. Reading a Psychrometer

11. Parts of a Psychrometer 1. Wet-bulb – water soaked gauze on a regular thermometer 2. Dry-bulb – regular thermometer 3. Handle – with attached wet and dry-bulb thermometers

12. How does a Psychrometer work? The dry-bulb thermometer shows the room temperature The dry-bulb thermometer shows the room temperature The wet-bulb thermometer shows temperature dropping as heat is taken from the thermometer and water evaporates off of the thermometer and the gauze into the room The wet-bulb thermometer shows temperature dropping as heat is taken from the thermometer and water evaporates off of the thermometer and the gauze into the room Using a chart and the wet and dry-bulb temperatures, you can find the relative humidity Using a chart and the wet and dry-bulb temperatures, you can find the relative humidity

13. Relative Humidity Chart Dry Bulb = 28 ºC Wet Bulb = 18 ºC Difference between wet and dry bulb = ? 10 ºC What is the relative humidity? 37%

14. Reminders when slinging a Psychrometer…… DO: DO: Be a safe distance away Be a safe distance away from your peers from your peers Hold the Psychrometer Hold the Psychrometer at a 90º angle, parallel at a 90º angle, parallel to the floor to the floor DO NOT: DO NOT: Let Go!!!! Let Go!!!!

16. Cloud Formation A cloud is billions of tiny water droplets suspended in the air. A cloud is billions of tiny water droplets suspended in the air. Clouds form as humid air is cooled to its dew point and condenses. Each cloud drop forms around a tiny bit of dust in the atmosphere. Clouds form as humid air is cooled to its dew point and condenses. Each cloud drop forms around a tiny bit of dust in the atmosphere. Water always needs a surface on which it can condense → this surface is called a condensation nuclei. Water always needs a surface on which it can condense → this surface is called a condensation nuclei.

17. Condensation Nuclei

18. Clouds continued… Cloud drops remain suspended in the atmosphere because they……. are so small! Cloud drops remain suspended in the atmosphere because they……. are so small! When billions of these water droplets come together, a cloud is formed. When billions of these water droplets come together, a cloud is formed. Clouds are classified according to their shape and altitude. Clouds are classified according to their shape and altitude.

19. The Main Types of Clouds

20. 1. Stratus – gray, smooth clouds Layered, can cover the whole sky Layered, can cover the whole sky Low Clouds, made of water Low Clouds, made of water Stratus clouds at the Earth’s surface are called fog Stratus clouds at the Earth’s surface are called fog

21. 2. Cumulus – puffy “cotton ball” like clouds Fair weather clouds Fair weather clouds Middle clouds, made of water and ice Middle clouds, made of water and ice

22. 3. Cirrus Clouds – high altitude clouds Feathery, wispy Feathery, wispy High clouds, made of ice High clouds, made of ice

23. Cumulonimbus Clouds - These clouds are thunderstorm clouds - “nimbus” means rain - They form from convective updrafts and downdrafts in a cumulus clouds

24. Precipitation - As long as cloud droplets remain small, they will remain suspended in the air. - When water droplets in a cloud reach.2 mm in size, they become too large to remain suspended and fall to the ground as precipitation. remain suspended and fall to the ground as precipitation. - Air temperature determines whether the droplets will fall as rain, snow, sleet, etc.

25. Types of Precipitation Rain – drops of water that fall Rain – drops of water that fall in temperatures above freezing Snow – forms when air temperatures are so cold that water vapor changes directly to a solid Snow – forms when air temperatures are so cold that water vapor changes directly to a solid Sleet – forms when snow passes Sleet – forms when snow passes through a layer of warmer air, melts, and then refreezes near the surface.

26. Freezing Rain – forms when snow melts and Freezing Rain – forms when snow melts and then cools to below freezing in cold air; it remains a liquid however and does not become ice unit it hits something on the surface (black ice) Hail – forms in cumulonimbus clouds; drops of water freeze around a small nucleus of ice. As the ice is tossed up and down by air currents within the cloud they grow larger. When they grow too large to remain suspended, they fall to the ground (the strength of the air currents determines how large a hailstone will become) Hail – forms in cumulonimbus clouds; drops of water freeze around a small nucleus of ice. As the ice is tossed up and down by air currents within the cloud they grow larger. When they grow too large to remain suspended, they fall to the ground (the strength of the air currents determines how large a hailstone will become)

27. Hail is the most damaging form of precipitation! Hail is the most damaging form of precipitation!

28. Severe Weather

29. Thunderstorms result from the rapid upward movement of warm, moist air result from the rapid upward movement of warm, moist air can occur at frontal boundaries (cold) and also within warm, moist air masses (late afternoon thunderstorms) can occur at frontal boundaries (cold) and also within warm, moist air masses (late afternoon thunderstorms) Thunderstorms with winds in excess of 89 kph are considered severe Thunderstorms with winds in excess of 89 kph are considered severe

30. Thunder and Lightning Cumulonimbus clouds cause static charges (positive and negative) to build up as they move across the sky Cumulonimbus clouds cause static charges (positive and negative) to build up as they move across the sky Lightning occurs when a Lightning occurs when a current flows between these current flows between these regions of opposite charges regions of opposite charges between the sky and the between the sky and the ground or cloud to cloud. ground or cloud to cloud.

31. Thunder Thunder – results from the rapid heating of the air around a bolt of lightning (temperatures reach 30,000ºC) You can tell how far away a lightning strike is by counting the number of seconds between the lightning and thunder (5 sec = 1 mile) You can tell how far away a lightning strike is by counting the number of seconds between the lightning and thunder (5 sec = 1 mile)

32. Tornadoes - violent whirling wind that moves in a narrow path over land - form in severe thunderstorms; winds inside tornado can be over 300 mph - The US has many more tornadoes each year tornadoes each year than any other than any other country in the world; country in the world; Tornado Alley Tornado Alley

33. Hurricanes - large, swirling low pressure systems that form over tropical oceans - Form between 5 and 20 degrees North Latitude - Hurricane season lasts from June to November - Must have sustained (constant) winds of over 74mph - Largest and most destructive storms on Earth - Hurricanes get their energy from the warm, moist ocean; when they hit land they begin to die out! ocean; when they hit land they begin to die out!

34. Hurricanes

35. Pressure Systems

36. High Pressure Systems – cold, dense air that is sinking Spins clockwise in the Northern Hemisphere Spins clockwise in the Northern Hemisphere Also known as an anticyclone Also known as an anticyclone Associated with clear, fair weather Associated with clear, fair weather (Remember, clouds don’t form when cool air is sinking!) The High Pressure Symbol on a weather map

37. Low Pressure Systems – warm, rising air Spins counterclockwise in the Spins counterclockwise in the Northern Hemisphere Northern Hemisphere Also known as a cyclone Also known as a cyclone associated with cloudy weather associated with cloudy weather (warm, rising air cools as it rises, reaches its dew point, and forms clouds – clouds can lead to precipitation) (warm, rising air cools as it rises, reaches its dew point, and forms clouds – clouds can lead to precipitation) The Low Pressure Symbol on a weather map

38. Isotherms and Isobars

39. Isobars – connect points of equal barometric pressure on a weather map (used to identify Highs and Lows on a weather map) Isobars – connect points of equal barometric pressure on a weather map (used to identify Highs and Lows on a weather map) close isobars = windy conditions close isobars = windy conditions Isotherms – connect points of equal temperature on a weather map Isotherms – connect points of equal temperature on a weather map

40. Fronts A change in weather from one day to the next is due to the movement of air masses. A change in weather from one day to the next is due to the movement of air masses. Air masses with different temperatures and humidity do not mix well together! Air masses with different temperatures and humidity do not mix well together! Front – boundary between any two air masses of different densities Front – boundary between any two air masses of different densities

41. Warm Fronts Forms when a warm air mass meets and replaces a cold air mass Forms when a warm air mass meets and replaces a cold air mass Cirrus clouds often signal the advance of a warm front Cirrus clouds often signal the advance of a warm front Nimbostratus clouds often produce steady rain Nimbostratus clouds often produce steady rain

42. Warm Front

43. Cold Fronts Cold Fronts Forms when a cold air mass meets and replaces a warm air mass Forms when a cold air mass meets and replaces a warm air mass Cumulus and cumulonimbus clouds form & produce heavy rain and thunderstorms Cumulus and cumulonimbus clouds form & produce heavy rain and thunderstorms The leading edge of a cold front is much steeper than a warm front The leading edge of a cold front is much steeper than a warm front

44. Cold Fronts

45. Stationary Fronts Stationary Fronts Fronts that do not move forward are called stationary fronts Fronts that do not move forward are called stationary fronts Sometimes pressure differences can cause a warm or cold front to stop moving forward Sometimes pressure differences can cause a warm or cold front to stop moving forward Light wind and precipitation all along this type of front Light wind and precipitation all along this type of front These can remain in place for several days These can remain in place for several days

46. Occluded Fronts Occluded Fronts If a cold front catches up to a warm front the result is an occluded front If a cold front catches up to a warm front the result is an occluded front Two cold air masses meet and force a warmer air mass between them to rise Two cold air masses meet and force a warmer air mass between them to rise Strong winds and heavy precipitation may develop Strong winds and heavy precipitation may develop

47. Occluded Front

48. At each frontal boundary you will find: At each frontal boundary you will find: Low Pressure – because along all fronts warm air is being forced upward, cooled to its dew point, and condensing to form clouds Low Pressure – because along all fronts warm air is being forced upward, cooled to its dew point, and condensing to form clouds Precipitation is found at most frontal boundaries! Precipitation is found at most frontal boundaries!

49. Weather Forecasting

50. Meteorologist – a scientist who studies the weather; they make observations to use Meteorologist – a scientist who studies the weather; they make observations to use on weather maps and to make weather forecasts on weather maps and to make weather forecasts Modern-day weather forecasts are based on computer weather models Modern-day weather forecasts are based on computer weather models Different models may produce different predictions Different models may produce different predictions These models cannot predict the weather perfectly, therefore meteorologists use more than one model and make predictions accordingly These models cannot predict the weather perfectly, therefore meteorologists use more than one model and make predictions accordingly

51. National Weather Service – issues weather advisories when severe weather is observed or could occur National Weather Service – issues weather advisories when severe weather is observed or could occur Weather Watch – prepare for severe weather that is observed or could occur in your area Weather Watch – prepare for severe weather that is observed or could occur in your area Weather Warning – severe weather conditions exist in your area and you should take immediate action Weather Warning – severe weather conditions exist in your area and you should take immediate action

52. Weather Forecasting Weather Station Model – created by meteorologists, they contain information about the weather at a specific location Weather Station Model – created by meteorologists, they contain information about the weather at a specific location These are provided by meteorologists from all over the world These are provided by meteorologists from all over the world They are uniformly written so any meteorologist can read them They are uniformly written so any meteorologist can read them

53. Example of Weather Station Model

54. Determining Air Pressure on a Weather Station Model Rule #1 If the number begins with a 7, 8, or 9, you will add a 9 in front of the number and a decimal point before the last number. Example: 994 → 999.4 mb

55. Pressure Rules Continued… Rule #2 If the number begins with a 0, 1, or 2, you will add a 10 in front of the number and a decimal point before the last number. Example: 046 →1004.6 mb

56. Change in Pressure Rules Rule #1: A plus sign (+) means it went up the last three hours A minus sign (-) means it went down the last three hours Rule #2 If there is two numbers, the decimal goes in between the numbers. If there is one number, the decimal goes before the number. Examples:+ 5 → up.5 mb - 12 → down 1.2 mb

57. Station Model Practice a) Temperature – b) Dew Point – c) Pressure – d) Change in Pressure – e) Cloud Cover – f) Wind Speed – g) Wind Direction – 45 42 841 -7

58. Climate Climate – the average of all weather conditions over a long period of time (30 years) Climate – the average of all weather conditions over a long period of time (30 years) The Three Major Climate Zones on Earth

59. Climate Zones Tropics Tropics Fall between 23.5º North (Tropic of Cancer) and 23.5º South (Tropic of Capricorn) latitude Fall between 23.5º North (Tropic of Cancer) and 23.5º South (Tropic of Capricorn) latitude Always receive the most direct rays from the sun Always receive the most direct rays from the sun Warm temperatures year round Warm temperatures year round

60. Polar Zones Polar Zones Fall between the Poles to 66.5º North and 66.5º South latitude Fall between the Poles to 66.5º North and 66.5º South latitude Always receive indirect rays from the sun Always receive indirect rays from the sun Cold temperatures year round Cold temperatures year round Temperate Zones Temperate Zones Fall between the Tropics and Polar Zones Fall between the Tropics and Polar Zones Weather generally changes with the seasons Weather generally changes with the seasons In the summer the sun’s rays are more direct so it is warmer and in the winter the rays are less direct so it is cooler In the summer the sun’s rays are more direct so it is warmer and in the winter the rays are less direct so it is cooler

61. Within each zone, a number of factors can affect weather patterns. Large bodies of water – have a moderating effect; coastal areas are warmer in the winter and cooler in the summer Large bodies of water – have a moderating effect; coastal areas are warmer in the winter and cooler in the summer Mountains – act as barriers over which winds must flow Mountains – act as barriers over which winds must flow

62. Windward and Leeward Sides of a mountain