Pressure Maps
 Take a look at the map and discuss what you notice
with your group.
 Air pressure is important for understanding weather!
Labeling Parts of a Pressure Map
 The numbers- represent atmospheric pressure measured in
millibars. The pressure changes from place to place across
the U.S.
 The lines across the U.S. are isobars (iso= same; bar=
pressure). The isobars connect all of the recording stations
where the atmospheric pressure is the same.
Meteorologists know the pressures at the recording
stations and estimate where to draw the lines between
stations.
 The letters H and L on the map show where the pressure is
highest and lowest in a region. The numbers on the isobars
moving away from the H get smaller, and the numbers on
the isobars moving away from the L get larger.
Looking for Highs and Lows
 What is the lowest pressure reading on the map?
 What is the highest pressure reading on the map?
 Locate the low and high pressure areas on the map.
 Which direction do you think the wind is blowing, from
Billings, MT, to Kansas City, MO or from Kansas City to
Billings?
 Which direction do you think the wind is blowing, from
Kansas City to Buffalo, NY, or from Buffalo to Kansas
City?
Explore Isobar Intervals
 What is the interval, or difference, between isobar
lines?
 The pressure difference between two adjacent lines is
always the same (4mb), but the distance is not always
the same. What do you think that tells us?
 What do you think it means when the lines are father
apart?
 What could the distance between isobars tell us about
how fast the wind is blowing?
Nature’s Balancing Act
 When you see areas of high pressure and low pressure
on a weather map, think about what happens to
balance the difference. Air flows from areas of high
pressure towards areas of low pressure. This air
movement is called WIND!