1934 ] 
Mosquito Investigations in Alaska 
205 
cause storms and precipitation on the southern slopes of the 
Alaska Range. Occasionally a low pressure area will move 
through the interior, coming up from the Bering Sea. These 
give southerly winds throughout the interior. During the 
summer the heated interior of Alaska is conducive to low 
pressure areas of slight intensity which, in turn, induce 
precipitation. 
The precipitation over the greater part of the interior is 
small. Around Fairbanks it averages from 10 to 14 inches. 
About 25% of this occurs in the form of snow. Normally 
the wettest months are July and August with June and 
September following. These four receive over half the 
year’s precipitation. Over a period of 15 years the records 
show that the wettest years gave over twice the precipitation 
of the dry years. This disparity is due largely to the ex- 
cess of rainfall in the summer months of the wet years and 
a deficiency of rainfall in dry years rather than marked 
changes from normal in other months. Around Fairbanks 
snow is usually gone by the last of April, although an occas- 
ional fall of snow in May or June is not uncommon. During 
the summer months rainfall is sometimes attended by mild 
thunderstorms and sometimes hail. 
The summers of interior Alaska have delightful tempera- 
ture conditions. They are warm enough for comfort, but 
are not oppressively hot. The long days and continuous 
sunshine cause rapid growth of vegetation. The highest 
temperature ever recorded over many years was 100° F. at 
Fort Yukon in July, 1915. The spring months have the 
highest percentage of possible sunshine and the late fall and 
the early winter months the least. Fairbanks averages 17 
clear days in April and only 8 in September. Winter tem- 
peratures are as low as 75° F. 
The situations in which mosquito larvas were found de- 
veloping fall into two fairly well defined categories. The 
first included those areas in which the water was present 
during the greater part of the summer while the second 
included those areas in which the pools were temporary in 
