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.

14.
Weather Charts
• Weather Charts have lots of symbols and
information.

15.
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

16.
Pressure Systems
• High pressure: typically fair weather 
• Low pressure: typically cloudy, unstable
conditions… Bad weather 
• General movement: west to east in the US

17.
Can you read this map?

18.
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?