19201 METEOROLOGY. 619 



nishod by tho native grasses. . . . The ' opeuness ' of tho winters encourages 

 grazing. . . . 



"Tin' chief climatic liandicaps are (1) irreguhirity in the amount and dis- 

 tribution of procii)itation, and (2) iiiiscasoniiljlo low temperatures in the grow- 

 ing season. Periods of drouglit are common, but the soutlieastrrn quarter of 

 the State never has had a general failure of both the corn and small grain 

 crops. In the western part of the State especially, the normal amount of rain 

 in some years may fall in such short, heavy showers that most of it runs off 

 and thus is of little benefit to the crops. Late killing frosts in the spring are 

 not infrequent and are a menace to fruit growing and occasionally injurious to 

 corn. Early autumn frosts occasionally damage corn and flax crops especially 

 in tho northern sections. . . . 



" The mean annual temperature of the State is about 45° F., for the eastern 

 half about 44. .5°, and for the western half about 4.5.6°. The northern counties 

 have an annual mean about 5° lower than the southern countries. . . , 

 Maxima temperatures of over 100° have been recorded for most of the stations 

 outside the Black Hills, and minima temperatures below — 40° having been 

 recorded from most of the long-established stations except those in the Black 

 Hills region. The extremes for the State are 115 and — 50°, a range of 165°. 

 Several stations have recorded an annual range of more than 150°. . . . 



" The interval between the last killing frost in the spring and the first in 

 the autumn — the crop-growing season — averages nearly 130 days. For the 

 northern half of the State it is nearer 120 days, and for the southeastern quar- 

 ter it is 140 days. The northern border has the shortest season (115 days) and 

 the lower Missouri Valley the longest (150 days). The frost-free period 

 around the base of the Black Hills and on the slopes of some of the buttes 

 where there is good air drainage is a week or two longer than the average for 

 the State. . . . 



" Because of the low relative humidity, high summer temperatures, and per- 

 sistent wind, the rate of evaporation is high. Experiments have shown that in 

 most parts of the State evaporation from a water surface would amount to 

 about 40 in. annually. In the northeast corner, however, it would be only 

 30 in. and in the southwest corner over 50 in. . . . 



" The average annual precipitation in South Dakota is approximately 20 in., 

 in the eastern half about 22.3, in the western half about 17 in. In the former 

 83 per cent, and in the latter 81 per cent, usually is received between March 

 1 and September 30. The amount of rainfall decreases toward the west and 

 north. Becau.se of the increased altitude, the central portions of the Black 

 Hills receive more precipitation, especially snow, than do the surrounding 

 plain.s." 



The evidence does not indicate that the climate of the State is changing. 



Tornadoes occur, especially in the southeastern part of the State, but are 

 very irregular in distribution, and the area affected is very restricted. The 

 blizzard, which has given the State a reputation for severe winters, is much 

 less frofpient than is generally supposed by nonresidents, "and as a result of 

 the conditions attending: tho settlement of the rural districts, the construction 

 of more comnuKlious and more substantial farm buildings, fencing, and the 

 more complete preparation for winter, such storms should be much less Injurious 

 than formerly. ... 



" It is not unlikely that the extension of the tilled area has reduced the 

 Injury inflicted on any given locality by hot winds. . . . Nevertheless, winds 

 which are very drying still occur, and If their occurrence coincides with a 

 period of deficient soil moisture, vegetation suffers severely, especially sorts 



