1. L.O: SWBAT to determine dewpoint and relative humidity.
Do Now: take your reference table, a PENCIL, and a scrap piece of paper (you can share (you only need half of the paper, must have 1 straight line) or grab one from the back by the printer.

2. When weather people know the relative humidity and the air’s dewpoint they can predict rain.

3. Dew Point Temperature
Dew Point – The temperature at which air becomes saturated with water vapor.

4. When air is cooled to the dew point, condensation occurs.
The dew point temperature depends on the amount of water vapor in the air.
The closer the dew point gets to the temperature, the better the chance of precipitation. (*Important*)

5. Relative Humidity
Relative Humidity – Compares the actual amount of water vapor in the air with the maximum amount of water vapor that the air can hold. (Tells you how much water vapor is in the air)
Relative Humidity is expressed as a percent (%)

6. Relative Humidity is constantly changing
Relative Humidity changes based on:
1) Temperature
2) The amount of water vapor

7. Relative Humidity & the Amount of H2O
The Box can hold 20 molecules
Relative Humidity & the Amount of H2O
20/20
15/20
10/20
5/20
100% % % %

8. Cold Air
WARM AIR
vs.
Warm Air is Less Dense
Cold Air is More Dense

9. Cold Air WARM AIR vs. Cold Air holds LESS Water Vapor Warm Air holds
Warm Air is Less Dense
Cold Air is More Dense
Cold Air holds LESS Water Vapor
Warm Air holds
MORE Water Vapor

10. Relative Humidity & Temperature
The amount of water vapor that air can hold depends on the temperature.
Warm Air can hold more water vapor

11. When the relative humidity is near 100% , it rains
When the relative humidity is near 100% , it rains! Because the air is saturated & it can’t hold anymore moisture!

12. Turn to ESRT pg 12. used to find dewpoint

13. This chart is used to calculate the relative humidity

14. this is a psychrometer: psychrometer is used to determine dew point and reletive humidity.

15. a Psychrometer is just two thermometers
a Psychrometer is just two thermometers. One thermometer is called the “dry bulb”(can also be called air temperature), the other is called the “wet bulb”

16. How can we determine dewpoint temperatures?
Step 1. WRITE OUT the wet bulb and the dry bulb temperatures.
Step 2. Calculate the difference between wet bulb and dry bulb. (also known as the depression)
Step 3. Take out your ESRT’s and turn to page 12

17. Step 4. Locate the dry bulb temperature reading on the left side of your chart.
Step 5. Locate the difference between wet bulb and dry bulb on the top of your chart.
Step 6. DRAW A LINE IN PENCIL TO DETERMINE THE DEW POINT!

19. 1. If the dry bulb is 11oC and the wet bulb is 8oC.
2. What is the wet bulb temperature if dry bulb is 16oC and the dewpoint temperature is 9oC?
5 degrees C
12 degrees C

20. Relative Humidity
You can determine the % Relative Humidity the SAME way you found the dewpoint temperature on the chart in the ESRT’s.
What happens to the relative humidity as the air temperature approaches the dewpoint temperature?
It increases!

21. Relative Humidity
1. What is the percent relative humidity if the Air Temperature is 20oC and the Wet Bulb is 11oC?
2. What is the percent relative humidity if the Dry-bulb temperature is 14oC and the Wet- bulb temperature is 14oC?
30%
100%

22. EXIT TICKET Fill in the chart
EXIT TICKET Fill in the chart. Depression= difference between Wet&Dry bulb
4oC
24oC
72%
11oC
5oC
54%
17oC
15oC
20oC
74%
3oC
16oC
74.5%