50 FOREST DISTRIBUTIOX 



-17.2 degrees. For the elimatologieal sections established by the 

 Weather Bureau, the mean annual temperatures range as fol- 

 lows : 



Northeastern ilontana 39.6 to 43.3 degrees 



Southeastern Montana 42.9 to 47.2 degrees 



North Central Montana.. 36.8 to 45.8 degrees 



Southwestern Montana 34.1 to 4.5.5 degrees 



Western Montana ...38.9 to 45.8 .-legrees 



Northeastern ilontana is characterized by lower tempera- 

 tures usually and by higher winds and more su^dden changes of 

 temperature than other parts of the state. There is a sudden 

 transition from ^\inter to summer in the middle of June, from 

 snows and freezing weather to the long hot days of summer ; 

 autumn is dry, and mild weather often extends to December. 

 The normal temperature for April is about 40 degrees, which 

 marks the beginning of the spring growth of the prairie flora. 

 In the southeastern part of the State there is a wider range 

 of temperature, both daily and anniial. During the summer 

 the diurnal variations may be as much as 40 degrees or more. 

 Snow falls from October to ^larch. The north central portion 

 of the State is colder and drier than the northeastern part. The 

 winter minimum sometimes falls to 45 degrees below zero, and 

 the summer maximum of 100 degrees is experienced in many 

 localities. In southwestern ilontana the several high ranges of 

 mountains collect abundant snows. High altitudes, low humid- 

 ity and the absence of high winds are features of this section. 

 The tefnperature records are more uniform than might be ex- 

 pected, owing probabh' to the more or le.ss sheltered locations 

 of the various stations of observation. Western ^Montana is a 

 region of widely differing altitudes and topographic conditions, 

 and in some of the mountain valleys frosts and even snows may 

 occur in all months of the year. In some parts the snowfall is 

 exceedingly heavy. 



Two tables are provided aiving the significant facts of at- 

 mospheric temperatures. Table 5 gives the average mean tem- 

 peratures during the months of the growing season and the 

 average annual means at 29 different stations in the State. The 

 last six are within the timbered section of Montana and in 

 proximity to important forests. The others are mostly in the 



