Book 7, Question 60
Why Do H and L Letters Appear on Weather Maps?
On a weather map, a big H marks the center of an area of high pressure. A big L marks the center of an area of low pressure. They are the main characters in the weather story, and they help us guess what is coming.
From the book
Page from A Million Whys Book 7
More fun facts
- On many weather maps, the center of a high-pressure area is marked with a blue H.
- In the United States, air pressure is usually measured in inches of mercury or millibars.
- Normal air pressure at sea level is 29.92 inches of mercury, or about 1013 millibars.
- Inches of mercury refers to the height of a column of mercury, the liquid metal used in some barometers.
- Fronts on weather maps grow out from the L's, the centers of low pressure.
Sources: NASA Science, NOAA, NOAA
Questions kids ask
What is normal air pressure?
About 29.92 inches of mercury, or 1013 millibars, at sea level.
What color is the H on a weather map?
It is often blue.