202 Alaskan Science Conference 



high latitude there is a long day of over 20 hours during June 

 and part of July with a high percent of possible sunshine during 

 the months of May to August, as is shown on Table 2. There 

 are over 9 hours of sunshine daily during these months. 



During the winter months days are short and temperature is 

 low, sometimes with — 5o°F. and even — 6o°F. recorded in the 

 mainland of Alaska during the month of January. However 

 these low temperatures are associated with windless days or 

 "calms" occurring in December and January. These calms and 

 clear sky make winter cold more pleasant than windy cold 

 weather in the coastal regions of Alaska. The cold winter 

 weather of the interior of Alaska is connected with the Siberian 



Table 2.— Character of the day and number of sunshine hours, normal at 



Fairbanks, Alaska 



Month Clear 



April 11 



May 7 



June 6 



July 7 



August 5 



September 5 



anticyclonic high pressure prevailing at this time in the northern 

 hemisphere. 



Prevailing winds in the valley are southwestern in summer 

 and northern in winter with low velocity of 5 miles per hour. 

 The frostless period in Fairbanks, located at the center of the 

 region, extends from May 29 to August 26, or 89 days. How- 

 ever there is great variability, the season extending in some 

 years over 135 days. 



The amount of the thermal units— degree days during the 

 growing season in various parts of the region is shown on 

 Table 3. In this table three types of the thermal units are 

 indicated: (A) number of degree days above freezing point 

 32°F. (o°C), (B) degree days about 41 °F. (5°C), temperature 

 which is considered by plant physiologists as a minimum for 

 the beginning of plant growth, and (C) degree days above 



