Handbook of Nature-Study · Lesson CCXXIV · Topic 36: Water and weather
224. How to read weather maps
Goal: Your child can find the highs, lows and isobars on a weather map, follow a storm across three days, and keep a daily weather record.
You'll need
- Weather maps for three days in a row (printed or saved from your national weather service's website)
- Red and blue pencils and a ruler
- An outdoor thermometer
- A nature notebook and a pencil (colored pencils if you have them)
What's in the book
The lesson has a leading thought, a method using maps for three successive days, sixteen observations on isobars, highs and lows, winds, isotherms and storms, a second set on tracking the highs and lows, and directions and a chart for keeping a daily school weather record.
The lesson, step by step
Get your maps
Save or print the surface weather map for the same hour on three days in a row. The book's maps came by telegraph; yours come from the internet, but they show the same things.
The leading thought
Weather maps are made with great care by the Weather Bureau experts. Each map is the result of many telegraphic communications from all parts of the country.
Highs and lows
Isobars are the curving lines that join places with the same air pressure.
Where is the greatest air pressure on your map? How high does the barometer stand there? How are the isobars arranged with reference to this region? What word is printed in the center of this series of isobars?
Find a center marked low. How high does the barometer stand there?
Do the winds blow toward this center or away from it?
What must the weather in the region just east of the low be? Why?
Follow the storm
On the first map of the series of three given, put an X in red pencil or crayon at the center of the high and a blue one at the center of the low
Mark the same centers on the next two maps, and join the marks with lines.
What do you find to be the general direction of the movement of the highs and lows?
How fast?
With your ruler find out how many miles one area of high or low has moved in twenty-four hours; in three days. Divide the distance which the area has moved in three days by three and this will give the average velocity for one day.
What we know now
Today's maps show pressure in millibars (1013 millibars is about 29.92 inches), and they add fronts: a blue line with triangles is a cold front, a red line with half-circles is a warm front. Forecasts now use weather satellites, radar, weather balloons sent up twice a day all over the world, and computers. They are good for about a week ahead.
Keep a weather record
The book says to read the weather at the same hours every day. Hang the thermometer at eye level on the north side of a post, not on a building, as the book advises. Each day write the date, hour, temperature, wind direction, clouds and any rain, snow, frost or fog. Stay indoors during thunder and lightning; record the storm from a window.
Nature notebook
Make a weather chart page with columns like the book's: Date, Hour, Temp., Wind, Cloudiness, Rain or Snow, Remarks.
Afterwards
Keep the weather record every day for a month (the book hopes for six months) and compare it with the maps once a week.
Answers to the book's problems
"High" is printed in the center of the ring of isobars with the highest pressure; "Low" in the center of the lowest. Winds blow out from a high and in toward a low (in the Northern Hemisphere they turn clockwise around a high and counterclockwise around a low). Highs usually bring fair weather; the area east of a low usually has clouds and rain or snow, because air rising into the low cools and its vapor condenses. Across the United States, highs and lows generally travel from west to east, taking several days to cross.
Worked out for this site from the scan. If a number in your copy differs, trust the book.