Forecasting the Weather 



8 9 



be foretold a few hours in advance by 

 the form and movement of the clouds. 



In the colder months, viz, November, 

 December, January, February, March, 

 and April, the winds are stronger than 

 at other seasons of the year, and storms 

 also move with greater rapidity. The 

 signs of falling weather in the colder 

 months ai e the formation of a high sheet 

 cloud covering the whole sky, an in- 

 crease in the temperature and moisture 

 of the air, and the change of the wind 

 to some easterly quarter. The precise 

 direction that the wind takes, whether 

 northeast, east, or southeast, varies for 

 different localities and the direction from 

 which the storm is approaching. In 

 New England, the Middle States, and 

 the Ohio Valley northeasterly winds 

 precede storms that approach from the 

 southwest, and southeasterly winds pre- 

 cede storms that approach by way of 

 the lake region. On the Pacific coast 

 southeasterly and southerly winds pre- 

 cede rain storms. In Wyoming and 

 other Northwestern States the heavy 

 snowstorms of winter and spring gen- 

 erally come from the north or north- 

 west with a strong wind from the same 

 direction. The direction of the wind 

 depends very much on the position of 

 traveling storms that pass across the 

 country. 



The storms of the cold season have 

 certain well-marked characteristics that 

 should be easily recognized by every 

 worker in the open air. These are: ( r ) 

 The changes in the aspect of the sky ; 

 (2) the direction of the wind before, 

 during, and after the storm ; and (3) 

 the shift of the wind, whether with or 

 against the sun. 



The clouds that precede the storm by 

 from twenty-four to thirty-six hours are 

 almost invariably light, wispy cirrus, of 

 the general character shown in Fig. 1. 

 Soon after the appearance of clouds of 

 this class a sheet cloud forms at a slightly 

 lower elevation and gradually thickens 

 until the sun is hidden. Figure 2 illus- 



trates the sheet cloud in the first stages 

 of formation. 



The subsequent clouds are much 

 darker than those above mentioned, and 

 appear to form at much lower elevations. 

 When the .sky becomes overcast the 

 wind generally freshens, the tempera- 

 ture rises, and the air becomes humid ; 

 in popular speech, " it feels like rain." 



LOW PRESSURE AND HIGH PRESSURE 



The weather experienced from day 

 to day depends upon the frequency and 

 the course followed by areas of low pres- 

 sure and the succeeding areas of high 

 pressure which generally follow them. 

 These are exceedingly variable both as 

 to direction and rate of movement. 

 Some move rapidly from the northeast- 

 ern Rocky Mountain slope to the mari- 

 time provinces of Canada at a uniform 

 rate, while others have a rapid rate 

 of progression at the beginning, but 

 quickly slow down and finally cease to 

 move. There are, however, certain 

 characteristics possessed by both highs 

 and lows, which, if once fully under- 

 stood, would greatly assist the individ- 

 ual observer in making a forecast of the 

 weather for the morrow. Figure 8 is a 

 reduced copy of the daily weather map 

 of December 15, 1892, and is introduced 

 to illustrate some of the characteristics 

 above mentioned. 



If we divide the diagram into four 

 equal parts by lines passing east and 

 west and north and south through the 

 word low, and calculate the average tem- 

 perature for each part or quadrant of 

 the oval figure, we will find it to be 17 

 for the northwestern quadrant, 50 for 

 the southwestern, 59 ° for the south- 

 eastern, and 35 for the northeastern. 

 The distribution of temperature is also 

 shown by the dotted lines (isotherms). 

 In the upper left-hand corner of the 

 diagram the temperature is io° below 

 zero ( — 10); between that line and the 

 one next below, temperature varies from 

 io° below to zero, and so on until the 



