MISSOULA, Mont. -

Every fire is different, but the root causes of wildfire can be broken down into three ingredients -- fuel, oxygen and an ignition source.

Our climate in western Montana is perfect for fire. The summer months are hot and bone-dry. Many days in a row without rain allows grass, shrubs, and trees to slowly dry out and become more likely to burn.

NBC Montana spoke with ecologist Matt Jolly at the Missoula Fire Lab. He studies how plants burn in different conditions.

"Fuels (trees, grass and other vegetation) are essentially like a sponge," Jolly said. "They absorb or release moisture to the atmosphere, and the more moisture a fuel has the less likely it is to ignite."

Jolly says that it's a long-term process, on a scale of weeks to months, to have fuel such as trees to dry out. Lighter shrubs and grasses can dry out over only a couple of weeks if conditions are exceptionally dry.

The weather doesn't stop interfering after a fire has started. The most dangerous days for firefighters are those with high winds and low humidity. Wind provides fresh oxygen to a wildfire, and strong enough winds can help fires create their own small-scale weather patterns, such as fire vortexes and large smoke columns.

Meteorologists with the National Weather Service issue a Red Flag Warning, also called a Fire Weather Warning, when winds are at least sustained at 20 miles per hour, gusting to 30 miles per hour, with relative humidity of 15 percent or less.

In cases where a lot of lightning is expected from dry thunderstorms, a Red Flag Warning can also be issued. The vast majority of fires caused by nature are caused by lightning.

Lightning-caused fires burn hundreds of thousands of acres in the Northern Rockies every year.

The factor that is most influenced by humans is the ignition source. Most of the time, natural causes are not to blame for starting a fire. According to the National Interagency Fire Center, 85 percent of all wildfires in the United States each year are caused by humans.

In 2013, the West Mullan Fire near Superior, and the Firestone Flats fire near Arlee were both caused by humans. Together, those fire burned more than 7,000 acres. In both cases the fires threatened homes.

Specific ignition sources range from campfires that aren't fully extinguished, sparks from lawn equipment, hot engine exhaust, fireworks, and even arson.

Experts urge everyone to be careful with fire during the summer, when one spark has the potential to start a massive blaze.