884 Handbook of Nature-Study 



LESSON CCXXIV 

 How TO READ WEATHER MAPS 



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. Every intelligent person 

 should be able to understand the weather maps. 



Method Get several weather maps of the nearest Weather Bureau Sta- 

 tion. They should be maps for successive days, and there should be 

 enough so that each pupil can have three maps, showing the weather condi- 

 tions for three successive days. 



Observations i . Take the map of the earliest date of the three. Where 

 was your map used ? What is its date ? How many kinds of lines are there 

 on your map ? Are there explanatory notes on the lower left-hand corner of 

 your map ? Explain what the continuous lines mean. Find an isobar of 

 30 ; to what does this figure refer ? Find all the towns on your map where 

 the barometer stands at 30 inches. Is there more than one isobar on your 

 map where the barometer stands at 30? 



2 . 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 ? 



3 . What do the arrows indicate ? What do the circles attached to the 

 arrows indicate? 



4. In general, what is the direction of the winds with reference to this 

 high center ? 



5. Is the air rising or sinking at the center of this area? If the wind is 

 blowing in all directions from a center marked high, what sort of weather 

 must the places just east of the high be having ? Do the arrows with their 

 circles indicate this ? 



6. Find a center marked low. How high does the barometer stand 

 there? Does the air pressure increase or diminish away from the center 

 marked low, as indicated by the isobars? Do the winds blow toward this 

 center or away from it ? 



7. What must the weather in the region just east of the low be ? Why? 

 Do the arrows and circles indicate this ? 



8. Is there a shaded area on your map ? If so, what does this show ? 



9. Compare the map of the next date with the one you have just 

 studied. Are the highs and lows in just the same position that they were 

 the day before ? Where are the centers high and low now ? In what direc- 

 tions have they moved ? 



10. Look at the third map and compare the three maps. Where do the 

 high and low centers seem to have originated ? How long does it take a high 

 or low to cross the United States ? How far north and south does a high or 

 low, with all its isobars, extend? 



n. What do the dotted lines on your map mean? Do they follow 

 exactly the isobars ? 



12. What is the greatest isotherm on your map? Through or near 

 what towns does it pass ? 



13 . Do the regions of high air pressure have the highest temperature or 

 the lowest ? Do high temperatures accompany low pressures ? Why ? 



14. What is the condition of the sky just east of a low center ? What 

 is its condition just west of low ? 



