12 



convective rain showers; the winters are cold and 

 dry. Principal accumulations of precipitation occur 

 in the form of rain in spring and early summer. 



Physical characteristics. 



1. Climate. 



a. Koppen climate classification: Type BSw, 

 a steppe climate east of the Continental 

 Divide that is typified by cold dry 

 winters, and convective summer storms 



(Visher 1954) . 



b. Regional macroclimate: The summer climate 

 of southeastern Montana is predominantly 

 hot and dry. Spring rains bring the 

 highest amount of precipitation, while 

 summer storms are largely convective and 

 somewhat drier. Winters are cold and dry, 

 with precipitation occurring mostly in the 

 form of snow. Broadus, the nearest long 

 term climatological station (923 m. (3,029 

 ft.) in elevation), is located 64 km. (40 

 mi.) to the east of the Custer National 

 Forest sites, and 30 miles north of the 

 Biddle area sites. The mean annual 

 temperature for the time period 1951-1980 

 at this station was 6.9 °C (44.5 °F) . For 

 this same time period, the mean maximum 

 temperature for July was 3 0.6 °C (87.0 



°F) , while the mean minimum for January 

 was -15.8 °C (3.6 °F) . Mean annual 

 precipitation was 33.9 cm. (13.84 in.) 

 (U.S. Department of Commerce 1982) . 



c. Local microclimate: Astragalus barrii 

 populations occur on all slope aspects; 

 however, in areas which lack an overstory 

 and receive full light, populations appear 

 to be established more often on northern 

 aspects, and are thus shaded during 

 portions of the day (pers. obs.). 



2. Air and water quality requirements: Unknown. 



3. Physiographic province: The range of A. barrii 

 lies in the Great Plains Province of the 

 Interior Plains; the western extension of the 

 Central Lowland (semiarid) as outlined by Hunt 

 (1974). 



