1. How is Weather Predicted?
Lesson 4-3
How is Weather Predicted?

2. Meteorology – study of weather
A. Instruments used to study weather:
1. Thermometer – measures air temperature
2. Barometer – measures air pressure (barometric pressure)
a. rising barometer -> increase in air pressure -> arrival of colder air
b. rising barometer -> less humidity -> lower chance of rain
c. falling barometer -> more humidity -> higher chance of rain

3. 3. Anemometer – measures wind speed
a. windsocks & wind vanes measure wind direction
4. Hygrometer – measures humidity
5. Observe the sky and clouds
a. Cirrus & small Cumulus clouds -> fair weather ahead
b. Large gray Cumulus clouds -> rain is probably on the way

4. Air Masses – large body of air that has the same temperature & humidity throughout
A. Take on characteristics of region over which they form
B. When weather changes in an area, the air mass over the area also changes
C. Change in air mass -> change in air pressure -> winds
D. Most move West to East in the U.S.

5. Front – border where two air masses meet (high pressure meets low pressure)
A. Most weather changes occur along fronts
B. High pressure usually is Cold, dense and dry air.
C. Low pressure is usually Warm, light and humid air.
D. A Warm front usually brings rain or snow that can last for hours.
E. A Cold front usually brings heavy rain for a short time, then clear cool weather.

6. Cold Front

7. Cold Front

8. Warm Front

9. Warm Front

10. Weather Maps – give information about what the weather is like in an area
A. Show:
1. sun/clouds/rain/snow
2. warm/cold fronts
3. temperature