25 



Average annual number of days with snow cover from 1 to 10 in 

 the extreme south to 30 to 60 in the extreme north. Average annual 

 frost-free season from 150 days northward to 220 days southward. 



REGION" 20, SOUTHERN BLACK SOILS 



Subhumid and mesothermal throughout ; precipitation deficient at 

 all seasons in the northwestern portion, adequate at all seasons in 

 the eastern fringe and southeastern portion. Intermediate in mois- 

 ture conditions between regions 16, 25, and 29. 



Average annual number of days with snow cover, 1 to 10 in the 

 north to less than 1 in the south. Average frost-free season, 220 to 

 more than 260 days, longest southward. 



REGION 21, NORTHERN PRAIRIES 



Subhumid, microthermal ; precipitation deficient at all seasons in 

 the north, changing to adequate at all seasons southward; drying* 

 winds and frequent droughts of more than 30 days occur in the, 

 western portion. 



Average annual number of days with snow cover from 60 to 90 in 

 the south to more than 120 in the north. Average annual frost-free 

 season from 100 days in the north to 160 in the south. 



REGION" 22, CENTRAL PRAIRIES 



Northwestern portion and western fringe subhumid, remaining 

 portions humid; northern portion microthermal, southern mesother- 

 mal; precipitation adequate at all seasons throughout. 



Average annual number of days with snow cover 30 to 60 except 

 in the southern part of the western portion, where it decreases south- 

 ward, ranging from 1 to 10. Average growing season 150 to 160 

 days in the northern portion to 180 in the southeastern portion and 

 230 in the extreme southwestern portion. 



REGION 23, WESTERN GREAT LAKES 



Western portion subhumid, eastern portion humid; microthermal; 

 rainfall adequate at all seasons. 



Average annual number of days with snow cover, 60 to 90 in the) 

 southern and southwestern portions to more than 120 in the northern 

 and northeastern portions. Average annual growing season 100 days 

 in the north to 150 days in the south, or in the southwest, 170 days. 

 Upper Peninsula of Michigan, 110 to 140 days. 



REGION" 24, CENTRAL GREAT LAKES 



Humid, microthermal, with adequate precipitation at all seasons. 

 Winter temperatures more moderate than in region 23. 



Average annual number of days with snow cover from 60 to 90 in 

 the southern half, from 90 to 120 in the northern half . Frost-free! 

 season averaging 110 days in the north to over 150 in the south 

 longest close to the lakes. 



