The radar map above from WeatherUnderground at 4 p.m. MST June 30 shows a large thunderstorm cell north and northeast of the fire at Yarnell, Arizona. The pointer is at Yarnell. At 10:55 a.m., according to data from the MODIS satellite, the fire was approximately a mile or so north and northeast of the town, between the town and the approaching thunderstorm. At that time and until after 4 p.m., the wind blowing from the south-southwest and the southwest, most likely would have caused the primary spread of the fire to be toward the northeast.
Animations of weather satellite images that afternoon HERE and HERE, show the development and movement of the thunderstorm into the fire area. The red “X” and circle mark the approximate location of the fire.