Southern California firefighters began on Friday to stem the growth of several destructive wildfires as much cooler and wetter weather blanketed the West.

Three major blazes erupted in mountain communities east of Los Angeles during a recent heat wave that pushed temperatures as high as 115 degrees. Together, the fast-moving fires displaced tens of thousands of people, burned dozens of homes and strained the state’s firefighting resources.

But firefighters have started to gain the upper hand as winds quiet, moisture levels increase and temperatures drop. Forecasters said that even cooler weather was expected next week and that there was a 30 percent chance that light rain would fall where the fires are currently burning.

“Weather-wise, we are in a starkly different situation than we were when these fires erupted,” said Jonathan Suk, a meteorologist with the National Weather Service’s San Diego office, which provides forecasts for a large swath of Southern California. Here’s what we know about the three major fires.

Fires ignite all the time, but it’s only under certain conditions that they turn disastrous. Those very conditions were in place earlier this month, when extremely high temperatures and low humidity levels baked California.

To make matters worse, California’s heavy rains in recent years have fueled thick plant growth. All of that vegetation turned to tinder after a warm summer and the brutal heat wave, leaving it primed to burn.

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