The National Weather Service (NWS) issued a “red flag warning” in eleven states on Friday as conditions are favorable for wildfires.

According to an NWS map, almost all of Wyoming is under a red flag warning, along with large parts of Idaho, South Dakota, Oregon, Nevada, Utah and Nebraska. Meanwhile, small parts of Northern California, Southern Montana, Northern Colorado and Eastern Washington have also been issued the same warning.

“A red flag warning is issued when we identify weather conditions that promote rapid spread of fire that could become life-threatening. This does not indicate a fire is underway. These conditions are occurring now or will soon begin,” the NWS explains in a message on her website.

Many of these red flag warnings won’t be in effect until tonight, when conditions are less ideal for a fire to start, although several regions in Montana, Wyoming, Nebraska and South Dakota are expected to keep the warnings in effect until Saturday afternoon .

The NWS issues red flag warnings to warn people of critical fire conditions that increase the risk of wildfires starting and spreading quickly. These warnings are usually based on a combination of factors, including low humidity, high winds, dry vegetation and warm temperatures.

When humidity drops below a certain threshold, fires can start more easily, while strong winds can fan flames and cause fires to spread quickly. In addition, warm conditions or a long period without rain can dry out vegetation, providing ample fuel for fires; dry grasses, trees and shrubs ignite easily and burn quickly.

“Winds will increase as a Pacific cold front sweeps across the Pacific Northwest. Very dry air and breezy winds will be present over parts of central and eastern Oregon and southeastern Washington ahead of the frontal passage in the afternoon. As a result, this area will be susceptible to rapid fire spread,” the NWS office for Pendleton, Oregon said Friday morning.

Comparably low humidity and high winds are responsible for the fire hazard conditions in all warning states, with parts of Colorado possibly seeing record temperatures for this time of year.

“Guy west-southwesterly winds will develop across the higher terrain Friday afternoon. The strongest winds will be in Jackson County and far northwest Larimer County with gusts up to 30 miles per hour. In addition, relative humidity is expected to increase in the lower teens will decline,” NWS Denver/Boulder CO said. “On Saturday, gusty winds from west to northwest spread across much of north-central and northeastern Colorado. Temperatures will be very warm (possibly record-breaking), leading to relative humidity of 10 to 14 percent.”

This is because large parts of California are sweltering under unusually high temperatures. The NWS has issued several “heat advisories” and “extreme heat warnings” in Central and Southern California, predicting temperatures as high as 114 degrees in some areas.

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