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<br />. <br />o <br />z <br />z <br />. <br /> <br />- <br />~ <br />~ <br />~ <br />~ <br />" <br />z <br />u <br />E <br />" <br /> <br />OU1118 <br /> <br />FIGURE 5 <br />MONTHLY DISTRIBUTION OF AVERAGE ANNUAL PRECIPITATION <br />FOR REPRESENTATIVE LOCATIONS <br /> <br /> <br />.1 <br /> <br />" <br /> <br />'0 <br /> <br />, <br /> <br />o <br /> <br />"" <br /> <br />'" <br /> <br />"" <br /> <br />'" <br /> <br />... <br /> <br />lesser periods of deficient moisture may be interspersed <br />with periods of abundant precipitation. as may be noted <br />in figure 6 representing the weighted allnual precipita- <br />tion for the basin. <br />Most of the Great Plains. with the annual <br />precipitation varying between 12 anu 24 inches. agrkul- <br />lumBy is. a high risk area. Special farming practices are <br />required to conserve the moisture available, even under <br />normal conditions. <br />There are periods of extremely cold winter and hot <br />summer temperatures in the basin. Extremes range from <br />winter lows of - 60oF. in Montana to summer highs of <br />up to 110oF. in Nebraska. Kansas, and Missouri. The <br /> <br />. <br /> <br />,-' 20 <br /> <br />" <br /> <br />~ <br /> <br />HELENA,MONT. <br />BIS,",ARCK,NDAI( <br />DOoNEfl,COlQ <br />I KANSAS CITY, MO <br /> <br />JU"l~ <br /> <br />'UG <br /> <br />CCT <br /> <br />DEe <br /> <br />SEPT. <br /> <br />NO' <br /> <br />JUl."" <br /> <br />baSin regularly experiences over I DO-degree temperatures <br />in surllmer :md below.zero temperatures in winter over <br />most of its area. <br />One of the clim<.ltic facturs tlIat h3S an imp3ct on <br />much of the cultural and industrial activity III the basin. <br />but particularly agriculture, is the continuous period <br />with, temperatures above freezing conditions. The <br />freeze.free period is defined as the average number of <br />d~ys e~L'h 'ye~r between the last 320F. temperature in <br />the spring and the first 32oF. temperature ill autumn. <br />While the freeze-free periud does not completely define <br />the growing season for all crops and grasses, it is a <br />gener<lJ indicator of the most favorable period. Figure 7 <br /> <br />FIGURE 6 <br />WEIGHTED ANNUAL PRECIPITATION <br />IN INCHES - MISSOURI RIVER BASIN <br />1874 -1965 <br /> <br />" <br /> <br />190(\ <br /> <br />1910 <br /> <br /> <br />1920 <br /> <br />19~0 <br /> <br />19"10 <br /> <br />."' <br /> <br />1960 <br /> <br />\l <br />