Typically, this weather occurs due to westerly flow disturbance along the Arctic front. At the surface, the resultant anticyclones (high pressure areas) bring periods of high temperature and low humidity. This weather may last anywhere from a few days to a month.
High pressure ridges tend to develop over Alaska, the Yukon and the Northwest Territories of Canada. As summer progresses, the center of origination shifts to the east. Once formed, the ridges generally move in a southeasterly direction (Johnson, 1992, p. 19).
After a period of high temperatures, any breakdown in an atmospheric ridge can lead to forest fire. Thunderstorms and lightning are generally associated with the warmer, unstable air of low pressure areas. In addition, high and variable winds in front of or behind the atmospheric trough provide a mechanism for fire spread. Brotak and Refsnyder (1976) found that of major wildland fires in North America, most follow the passage of a cold front (Johnson, 1992, p. 19).
Once a forest fire has begun, a number of complex processes begin to occur. Initially, the fire spreads by heating and then igniting unburned woody and herbaceous fuels (Johnson, 1992, p. 22). This involves the evaporation of any remaining moisture within the fuel and the thermal breakdown of cellulose, as well as the ignition of volatiles to produce a visible flame. Heat is transferred primarily by convection and radiation as the front c