 Radio transmissions from Idaho to a weather service office in Riverton , Wyoming , indicated a dry weather front had pushed through and was heading east . It is believed that forest managers at the Wapiti ranger station received this information , but it did not reach the men on the fire lines because of a lack of radio lines . The USFS did have spotters in an aircraft providing aerial observation of the fire behavior that was radioed to the Wapiti ranger station . At 12 : 40 pm on August 21 , several spot fires were reported near the fire lines by aerial observers . At 1 pm , the weather at Wapiti was 90 ° F ( 32 ° C ) with an extremely low relative humidity of 6 percent . Winds blowing generally from the southwest increased to 30 miles per hour ( 48 km / h ) as the dry front approached at 3 : 30 pm . At 3 : 45 pm , they shifted abruptly from southwest to west , causing increased crowning and spot fires over the fire lines . Convectional winds also increased and the fire front started up the drainage heading east . 
