The Air Mass over Yosemite has changed. It gives the Firefighters an advantage.

A building and a pickup truck damaged by the Rim Fire in this United States Forest Service handout photo near Yosemite National Park, California, USA.

Reuters 
theguardian.com,
Monday 2 September 2013 16.52 EDT
 
Firefighters in California(click here)  gained ground on Monday against a massive wildfire burning part of Yosemite National Park, although complete containment may be weeks away, officials said.
Crews working through the night got an edge on the so-called Rim Fire, a 350-square mile (906-square km) blaze that has charred the California park's Northwest, said Andrea Capps, spokeswoman for the Rim Fire command center. They connected containment lines near the fire's northwestern and western borders, where most of the 4,500 homes threatened by the blaze are located, she said.
The fire was 60% contained by early Monday, a 15% increase from the night before.... 

This is when the high pressure in the Pacific began to close and water vapor moved in over the fire area. 

August 31, 2013
1430.19z
UNISYS Water Vapor Satellite of North and West Hemisphere

Below is the status of the air mass over Yosemite. Having the water vapor available over the fire region, which is at least six other major fires than Yosemite, will provide a shift back to enough humidity to reduce fire hazard. With an increase in humidity, the dangers of canopy involvement will reduce. Humidity has immediate impact on the canopies of the forests regardless of any sustained drought.

Example: If a flying ember lands on a small puddle of water on a leaf, it will diminish and extinguish the ability of the fire to ignite a larger danger. Do you put wet wood in a fireplace?

September 3, 2013
0930:18z
UNISYS Water Vapor Satellite of North and West Hemisphere (click here)