What is an isobar?

1
Lesson 31 What is an isobar?
2
A weather map shows us weather conditions from
many places. How is air pressure shown?
3
Air pressure is measured in millibars.
All of the weather stations call in their
measurements to the National Weather Service.
(remember that from unit 30?)
4
The meteorologists at the NWS put all of the
millibar numbers on their master map.
They then connect all of the places with the same
air pressure, with a line.
5
See those black lines?
They are called isobars.
Every place on one of those lines has the same
air pressure.
6
As you saw, isobars follow a curved path. The
ends meet to form a closed figure.
7
Connect the millibar readings with isobars
1025
1030
1025
1025
1035
1035
1030
1035
1030
1025
8
Did the numbers get higher, or lower as you go
toward the center?
They got higher, so the isobars show a high
pressure area.
9
Dry air weighs more than moist air. The more the
air weighs, the higher the pressure is.
Weather in a high pressure area is generally dry
and fair.
A high-pressure area is shown with a H in the
center.
10
Try this one
980
980
950
950
925
950
980
925
925
950
980
11
What do you notice about the numbers?
Higher or lower toward the center?
Because they went lower, it is a low pressure
area.
How do you think you mark a Low pressure area?
12
Moist air weighs less than dry air.
The less the air weighs, the lower the pressure
is.
The weather in a low pressure area is generally
cloudy or rainy.
A low pressure area is shown with an L in the
center
13
You may see a map such as this on The Weather
Channel.