We have all been hearing for the past 24 hours that gusty, changing winds were occurring at about the same time 19 firefighters near Yarnell went "out of contact." A study of several weather stations in the area gives a general idea of what was happening Sunday afternoon.
Temperatures were running in the upper 90s to 103 degrees near Yarnell. And for most of the afternoon hours, winds of 10 to 15 mph were blowing generally from the south or southwest. However, that all changed when a thunderstorm collapsed near the fire.
Near 5 p.m., we see a nearly 180-degree swing in wind direction, from the SSW to NNE and winds pick up to 25 with gusts to 43 mph. (This is at the stations we can access … gives us a good general idea of what happened, but not specific. Fire weather is very dramatic and changes over short distances.)
There is a YouTube video posted by Matt Oss from Phoenix, www.youtube.com/watch?v=OVbCtY31HpE, that documents the rapidly changing fire. It also shows the downdraft coming down out of the dying thunderstorm.