WEATHER 



Annual precipitation, growing season (April-Julyj precipitation, and winter 

 (November-March) precipitation data were compiled from weather stations to 

 document moisture availability for vegetation and waterfowl, as well as the 

 amount of winter precipitation, which influences snow cover. Average January 

 and July temperatures were monitored as well, since they relate to the amounts 

 of thermal stress experienced by wildlife during the months that typically have 

 the lowest and highest average temperatures. A "severe" winter can be 

 identified as one with lower than normal January temperatures and higher than 

 normal November-March precipitation (for example, the winter of 1978-79). 



Figures 1 and 2 summarize year-to-year weather changes at the Circle and 

 Fort Peck recording stations. Spring and summer 1980 were much drier than 

 normal; precipitation was similar to that in 1979, a drought year. Both annual 

 precipitation and growing season (April-July) precipitation were well below 

 normal at the Circle and Fort Peck recording stations (Figure 1). Because much 

 of the summer precipitation comes from isolated thunderstorms, precipitation in 

 the study area can be markedly different than at these two stations. Although 

 precipitation gauges were not installed in the study area until after the 

 monitoring period ended, Prodgers (1981) estimates that only 1.5 inches of 

 precipitation fell on the study area from January through July 1980. By 

 comparison, 1980 growing season (April-July) precipitation at Circle and Fort 

 Peck was 4.15 inches (10.5 cm) and 3.12 inches (7.92 cm), respectively (Figure 

 2). Total 1980 precipitation in the study area was estimated to be less than 8 

 inches (McKeever, pers . comm.); this compares to a total 1980 precipitation of 

 11.26 inches (28.6 cm) at Circle and 7.73 inches (19.6 cm) at Fort Peck. The 

 summer of 1980 was the second consecutive summer that the area experienced 

 drought conditions. Average July temperatures were near normal (Figure 1). The 

 winter of 1980-81 was quite mild, with very little snowfall and essentially no 

 snow cover in the Mine Study Area. Winter precipitation (November 1980-March 

 1981) was near or below normal at Circle and Fort Peck (Figure 2) and was 

 similar to that of the previous winter. Average January 1981 temperatures were 

 an unusual 15 degrees F above normal (Figure 1). 



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