PRESCOTT, Ariz. (AP) -- Higher humidity overnight helped make conditions at a deadly Arizona fire a bit less volatile.
But fire spokeswoman Karen Takai says the Yarnell Hill Fire is still zero percent contained, and thunderstorms that bring little rain and a lot of lightning are a major threat because of the dry vegetation.
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She says winds are calm Tuesday morning but thunderstorm cells were already visible.
At last count, about 500 firefighters are on the scene, with more on the way.
The Yarnell fire has burned about 8,400 acres, or about 13 square miles.
It killed 19 firefighters Sunday when they were overtaken by the flames.
For information on how to help Arizona fire victims , visit http://bit.ly/helpariz.