1. Meteorology Part 2: Weather Variables
Earth Science
Golodolinski/Black
2009

2. Part II: Weather Variables
Temperature
Air Pressure
Relative Humidity

3. Weather Variables 1. Temperatures Measured in °F Fahrenheit °C Celsius
The measure of the average kinetic energy
How fast the molecules move
Instrument used to measure temperature:
Thermometer
ESRT: Temperature conversion chart on p. 13
Measured in °F
Fahrenheit °C
Celsius °K
Kelvin

4. 1. Temperatures Shown on a weather map with:
Isotherms- Lines that connect places of equal temperature

5. ESRT: Temperature conversion chart on p. 13 & Chart Blank p. 183

6. ESRT: Temperature Conversion Chart on p. 13 Chart Answers p. 183

7. ESRT: Temperature Conversion Chart on p. 13 Temperature Chart Blank p

8. ESRT: Temperature Conversion Chart on p. 13 Temperature Chart Answers p. 183

9. Weather Variables 2. Air Pressure The weight of Earth’s Atmosphere
Changes depending on the temperature
Instrument used to measure pressure:
Barometer
Measured in inches and milibars

10. 2. Air Pressure Shown on a weather map with:
Isobars- Lines that connect places of equal barometric pressures

11. 2. Air Pressure Mercury barometer
As the air pressure pushes on the surface of the mercury in the dish, the mercury travels up the tube.
As pressure increases, the mercury rises in the tube.
Cool air sinks- causes higher pressure
As the pressure decreases, the mercury sinks out of the tube.
Warm air rises- causes lower pressure

12. ESRT: Pressure Conversion Chart p. 13

13. ESRT: Pressure Conversion Chart p. 13 Blank Chart p. 184

14. ESRT: Pressure Conversion Chart p. 13 Answer Chart p. 184

15. 2. Air Pressure
State the relationship between altitude and air pressure.
As the altitude increases, the pressure decreases
Draw the relationship on the graph.

16. Weather Variables 3. Relative Humidity
A ratio between the amount of moisture is in the atmosphere and how much moisture the atmosphere can hold
Measured in %
When the air is holding as much water vapor as it can, the air is saturated. When saturated, warm air contains more water vapor than cold saturated air.
When the air is saturated, the relative humidity is 100%
To summarize, when the water-vapor content of air remains constant, lowering air temperature causes an increase in relative humidity, and raising air temperature causes a decrease in relative humidity.

17. 3. Relative Humidity Temperature & Relative Humidity
The warmer the temperature is, the more moisture it can hold
State the relationship between temperature and relative humidity:
As the temperature increases, relative humidity decreases
Draw the relationship on the graph.

18. 3. Relative Humidity- Insturements

19. 3. Relative Humidity Dew Point Temperature
The temperature in which the air is saturated
100% relative humidity

20. Determining Relative Humidity and Dew Point Temperatures
Dry bulb
Air temperature
Wet bulb
Temperature an air parcel cooled by evaporation of water (wet cloth)
When given the wet bulb and dry bulb temperatures, you can determine the dew point temperature and relative by follow directions provided and using ESRT p. 12

21. ESRT: Dew Point Temp. p. 12

22. ESRT: Relative Humidity p. 12

23. Example 1 p. 186

24. Example 2 p. 186
p. 187 chart and #1-5

25. Practice Dew Point & Relative Humidity p. 187

26. Practice Dew Point & Relative Humidity p. 187 Answers

27. Practice Dew Point & Relative Humidity p. 187 #1-5

28. Condensation Gas to liquid
Change of phase from water vapor (gas) to liquid vapor (water)
Examples:
Water on cold glass of water, water on mirror after a shower, dew on grass, fog, clouds
Evaporation
Liquid to gas

29. 3 Things Needed for Condensation to Occur
Water vapor must be present
Air must be separated (relative humidity 100%)
Condensation nuclei (ex. dust particles)

30. Density of Air Warm air rises because it is less dense
Cold air sinks because it is more dense

31. Formation of Clouds Warm moist air rises
Air expands and cools due to the dew point
Air becomes saturated
Water droplets form on dust particles
Clouds consist of water droplets and ice crystals

32. Cloud Classification

33. Adiabatic Cooling
The cooling of a parcel of air as it rises through the atmosphere
Dry adiabatic lapse rate
rate of cooling or heating that applies only to unsaturated air.
dry air cools faster
Wet adiabatic lapse rate
rate of adiabatic temperature change in saturated air.
moist air cools slower

34. Cloud Formation by Adiabatic Cooling

35. Precipitation
Cloud particles (any form of water) too heavy to remain suspended in the air fall to Earth from a cloud
Examples: rain, hail, sleet, snow, freezing rain
What does precipitation do for the environment?
Cleans the air
ESRT p. 13 Present Weather

36. Forms of Precipitation
The type of precipitation that reaches Earth’s surface depends on the temperature profile in the lower few kilometers of the atmosphere.
Rain & Snow
In meteorology, the term rain means drops of water that fall from a cloud and have a diameter of at least 0.5 mm.
At very low temperatures (when the moisture content of air is low) light fluffy snow made up of individual six-sided ice crystals forms.
Sleet is the fall of clear-to-translucent ice.
Hail is produced in cumulonimbus clouds.

37. ESRT p. 13 Present Weather

38. Wind The horizontal movement of air
Caused by the uneven heating of Earth’s surface
Differences in air temperature cause differences in air pressure
The greater the difference in air pressure, the faster the wind

39. Wind Named by the direction in which they come from Isobars
Ex. North wind comes from the North
Isobars
Connect places of equal barometric pressure on a weather map

40. Wind Instruments Anemometer Wind vane Measures wind speed
Determines wind direction

41. Sea Breeze Water heats up slower than land:
High specific heat
Cooler temperatures
Air sinks
*HIGH pressure*
Land heats up faster than water:
Low specific heat
Warmer temperatures
Air rises
*LOW pressure*

42. Land Breeze Water cools down slower than land (stays warmer)
High specific heat
Warmer temperatures at night
Air rises
Land cools down faster than water
Low specific heat
Cooler temperatures at night
Air sinks

43. Sea and Land Breezes

44. Coriolis Effect
The deflection of winds and ocean currents caused by the rotation of Earth
Deflection is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere

45. Weather Factors Associated with Different Pressure Areas
High Pressure
Cool/ cold air
Air sinks/ goes down
Air moves outward
Clockwise
No clouds
No precipitation
Low Pressure
Warm air
Air rises
Air moves inward
Counter clockwise
Clouds
Precipitation likely

46. ESRT: Planetary Winds p. 14

47. p. 191 Weather Changes- adobe
Planetary Winds
p. 191 Weather Changes- adobe

48. Weather Changes p. 191

49. Weather Changes

50. Air Masses
Large region of the atmosphere with uniform temperature and humidity
ESRT p. 13: Air Masses

51. Air Masses Table

52. Air Masses Map

53. Fronts
The boundary between 2 air masses
ESRT p. 13 Front Symbols

54. Cold Front Cold air pushes the warm, moist air upward
Cold air is located behind the front
The greater the differences in temperatures, the more likely there will be a major storm
Usually pass quickly
Brings colder but clear weather conditions

55. Warm Front Warm air gently rolls over the colder air
Warm air is located behind the front
Conditions are usually cloudy and rainy for several hours
Usually pass slowly
Brings warmer but rainy weather conditions

56. Occluded Front
Occurs when a cold air mass overtakes a warm mass and overtakes another cold air mass
Precipitation is possible but not definite
Very slight temperature change

57. Stationary Front
Notice no arrows to show direction in the weather map symbols
Stationary means the front is not moving
Final direction of the movement is difficult to predict
Winds are blowing in opposite directions on each side of the front
Clouds can last for days

58. Fronts are usually associated with…
Clouds
Precipitation
Change in temperature
Change in wind direction
p.195 Station Models- Adobe

59. Station Models
On a station model, barometric pressure is ALWAYS written in a three-digit format
Converting from millibars:
Drop the 9 or 10 in the front of the number and loose the decimal point
Millibars
Station Model mb
093
984.2 mb mb

60. Station Models Station Model Millibars 146 1014.6 mb 457 986
Converting from the station model format to milibars
First:
If the first number on the station model is 0-4, place a 10 in front of the number
If the first number on the station model is 5-9, place a 9 in front of the number
Second:
Place a decimal point between the last 2 numbers
Station Model
Millibars
146 mb
457
986
p. 195

61. ESRT: Weather Map Symbols

62. Weather Stations

63. Draw a weather station using the following information:

64. Need to know: Dew Point & Air Temperature
The closer the air temperature is to the dew point temperature, the greater the chance for precipitation.

65. Determining Weather Station Values
6 stations on p. 197; Weather Map practice p #1-31; More questions p #1-22