438 ] Understanding the Weather 



OTHER CLOUD FORMS 



"Nimbus" is one of the descriptive words that are fre- 

 quently combined with the three cloud forms when dark, heavy 

 portions build up in them. For example, a cumulus that grows 

 black and threatening is a cumulus-nimbus, and a nimbo-stratus 

 is a rain sheet. 



"Alto" ("high") is also combined with cloud names, and 

 "fracto" ("broken") is another element of cloud descriptions. 

 Add these terms to combinations of main cloud forms like cirro- 

 cumulus and cirro-stratus and you have a descriptive name for all 

 the many cloud formations that decorate the sky. Cirro-cumulus 

 clouds are small and fleecy, arranged in even rows high overhead 

 and producing what we often call a "mackerel sky" a sign of 

 coming rain. 



How the Weatherman Operates 



Young children sometimes look upon "the weatherman" as a 

 very definite person either a hero or a villain, depending on how 

 well the weather fits in with their plans. Of course it does not take 

 long before they realize that this somewhat mysterious figure has 

 nothing to do with producing rain, snow, or sunshine he only 

 predicts them. In the next stage they begin to wonder why, when 

 predictions prove wrong for several days, we show any further 

 interest in them. 



FORECASTING THE WEATHER 



We can understand why some predictions fail to materialize 

 when we have a clear picture of the complex factors that enter 

 into weather forecasting. Our United States Weather Bureau has 

 more than five hundred observers stationed throughout the entire 

 country. Every morning each observer reports by teletype to head- 

 quarters in Washington, D. C. all the weather facts in his region 

 as recorded on sensitive instruments. These facts are all immedi- 

 ately recorded on a map by symbols. 



The Chief Forecaster studies this map, compares it with the 

 weather map of the previous day, and prepares his predictions for 



