The document explains various weather instruments, including thermometers, psychrometers, anemometers, and barometers, detailing how each measures temperature, humidity, wind speed, and air pressure. It outlines concepts like convection currents, isobars, and pressure systems, emphasizing their roles in weather forecasting. Additionally, it discusses interpreting weather charts and maps to predict weather conditions.

1. Weather Instruments
Anemometers, Barometers, Sling
Psychrometers, Thermometers, and Weather Charts.

2. Air Temp and Thermometer
• “Thermo” = Heat
– Measures the amount of heat
energy in the atmosphere.
– Heat comes from solar radiation
that was absorbed by the OZONE
layer in the Stratosphere and goes
into the air.
– Measured by THERMOMETER

3. Can you
read this
thermometer?

4. Humidity and Sling Psychrometer
• “Psychro” = Cold
– Measures the amount of water vapor in the air.
– Relative humidity is the current amount of water
vapor in the air compared to the total amount of
water vapor the air can hold.
• When the air is nearly completely filled with vapor, it
feels “muggy” if the air is hot. What word would you
use to describe humidity?
– Measured by PSYCHROMETER

5. Comparing Humidity Levels

6. How humid is it?
• If the
relative
humidity
of the air
is 88%...
How
would it
feel
outside?

7. Wind Speed and Anemometer
• “Anemo” = Wind
– Measures the wind speed in the air.
– Changes in the heating of Earths surface
(uneven), air temp, and air pressure cause air to
move
– Horizontal (side to side) movement of air: WIND
– Vertical (up and down) movement of air: AIR
CURRENT
– Measured by ANEMOMETER

8. Anemometer… Close Up!

9. Convection Currents or Cells
• Wind is caused by…
– Warm air rises because it is less dense, cooler
sinks because it is more dense.
– This pattern
is called a
convection cell

10. Air Pressure and Barometer
• “Baro” = Weight
– A barometer works by measuring the amount of
force exerted by the air’s molecules hitting a
surface area.
– Measured in millibars (mb)
– When air heats up, the molecules spread apart
and become less dense and the air pressure goes
down (becomes low pressure).
– Measured by BAROMETER

11. Reading a Barometer
• Can you read
this
Barometer?
• Standard air
pressure is
1013.25 mb.
Does this
barometer
read at
standard air
pressure?
1018 mb

12. Air Pressure and ISOBARS
• Isobar = (baros, meaning 'weight') is a line of
equal or constant pressure on a graph, plot, or
map.

13. ISOBARS – lines of pressure
The rules for drawing isobars are…
1. Isobar lines may never cross or touch.
2. Isobar lines may only pass through pressures
of 1000 + or - 4. In other words, allowable
lines are 992, 996, 1000, 1004, 1008, & so on.
3. The atmospheric pressure is given in millibars
(mb).
4. Low Pressure – increase with distance.
5. High Pressure – decreases with distance.

15. Weather Charts
• Weather Charts have lots of symbols and
information.

16. Fronts and Symbols
• Warm air mass behind a cold air mass
– warm front
• Cold air mass behind a warm air mass
– cold front
• Occluded fronts can signal weakening of
storm
• Stationary fronts prolong bad weather

18. Pressure Systems
• High pressure: typically fair weather 
• Low pressure: typically cloudy, unstable
conditions… Bad weather 
• General movement: west to east in the US

19. Can you read this map?

20. Map Questions…
• What is located where the rain is happening High or Low pressure?
• What do you notice the weather conditions
are like near the H’s?
• What type of front is located in the central
United States?
• What can you predict about future weather
conditions in Arkansas based on this map?