EXPERIMENT STATION BULLETINS. 697 



passes over Micliigan, and the precipitation is therefore ample and well 

 distributed through the year. Chart IX brings out this matter of 

 distribution in different portions of the state, as well as graphically 

 showing the amount of rainfall available in each place. 



CLOUDINESS. 



The amount of sunshine is an important element in climate both on 

 account of its relation to crop growth and development and the general 

 welfare and happiness of mankind. It probably ranks next after tem- 

 perature and precipitation, in importance. 



Like precipitation the range of latitude found in Michigan has no 

 appreciable affect on the amount of cloudiness, but on account of the 

 fact that the possible hours of sunshine increases, during the summer 

 season, with distance from the equator, the fact should be noted that 

 the days are more than thirty minutes longer in summer, in the upper 

 peninsula, than in the southern portion of the lower peninsula. 



The range of elevation in Michigan is hardly sufficient to cause an 

 appreciable difference in the amount of cloudiness but the influence of 

 the Great Lakes is decided. As was explained in connection with the 

 discussion of precipitation, the warm, moist air over the Lakes in 

 winter, is carried land-ward by the prevailing westerly winds, and 

 clouds are continuously formed, by condensation, when the colder land 

 areas are reached. The weather is therefore unusually cloudy in Michi- 

 gan during the late fall and winter months, especially in the western 

 half of the lower peninsula. In fact with the exception of portions of 

 New York state, along the eastern end of Lake Erie, and in the eastern 

 portion of the upper peninsula of Michigan, there is less sunshine along 

 the Lake Michigan shore than in any other section of the country. In 

 January the actual sunshine in western Michigan is less than twenty 

 per cent of the possible amount. 



During the warmer portions of the year, however, the Great Lakes 

 have just the opposite effect. The cool water tends to prevent convection 

 and clouds are not formed to the extent that they are in warmer sec- 

 tions. As a result the amount of sunshine is greater in July, bj^ about 

 ten per cent, in western Michigan then it is in Ohio and Indiana. 



The alternate passage of areas of high and low pressure over the state 

 results in fluctuating cloudiness. Low areas usually cause more or less 

 cloudiness for one or two days during their approach and passage and 

 these are followed by two or three days of clear weather, as the anti- 

 cyclones pass over. This change from cloudy to clear weather and back 

 again is not noticeable in the winter season to the extent that it is in 

 summer on account of the almost continuous cloudiness caused by the 

 lakes. In the summer time the cyclonic and anti-cyclonic formations 

 often become so feeble that they fail to cause the normal changes in 

 cloudiness and there are long periods of uninterrupted sunshine. 



WIND. 



The wind direction and velocity are important largely on account of 

 their relation to the other climatic elements. The direction of the pre- 

 prevailing winds, for example, is especially important in this state on 

 account of the position of the Great Lakes. If the prevailing wind were 



