• Haines, Donald A.
  USDA Forest Service: North Central Region
  
• Sando, Rodney W.
  USDA Forest Service: North Central Region
  

Weather conditions that increase the threat of forest fires are well known. Low precipitation and humidity, coupled with high temperature and maximum solar radiation, lower the forest fuel moisture and therefore increase the fire potential. Winds also play a part in this drying process. After ignition, wind force and direction are of great concern; high, variable winds make suppression difficult, and sometimes impossible.

Little detailed information exists on the characteristics of climatic conditions occurring before historical forest fires. In this paper we will attempt to quantitatively assess the "drought" conditions that preceded a number of great fires and to determine the climatic extremes referred to by such terms as "hot summer" and "low humidity." Sunshine records will also be examined, when available, and in some cases the general wind conditions and synoptic situations that immediately preceded these fires.