More than 15 million people across the central United States are under fire weather alerts through Friday, as a combination of heat, dry air and strong winds fuel risks of "extreme" wildfire behavior, forecasters said.

Within that group are roughly 3.8 million who face what the National Weather Service calls "critical fire weather" conditions on Thursday, according to the National Oceanic and Atmospheric Administration's Storm Prediction Center.

The critical risk area covers parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma and Texas the prediction center said. Broader sections of those states, as well as parts of Arizona, South Dakota and Wyoming, are seeing "elevated fire weather" conditions, which are slightly less intense.

Meteorologists define critical fire weather conditions as those that create favorable environments for wildfires to develop. Criteria includes high temperatures, low humidity and gusty winds, and a mixture of all three generally triggers red flag warnings.

The weather service has said it issues red flag warnings, or less urgent fire weather watches, "when the combination of dry fuels and weather conditions support extreme fire danger."

Alerts currently active in the middle of the country include red flag warnings, which means critical fire weather conditions are currently occurring or expected to occur shortly, and fire weather watches, which are issued when those types of conditions are farther ahead in the forecast, according to the National Weather Service. 

Several moderately populous metropolitan areas are located inside the risk area, including Albuquerque, Denver and El Paso, in addition to Amarillo, Texas, and South Dakota's capital, Pierre.

This bout of fire-prone weather partially stems from a storm system moving into central states on Thursday, bringing wind gusts of up to 50 or 60 mph to the Southern Plains, said CBS News meteorologist Nikki Nolan. At the same time, forecasters anticipate that relative humidity values in the region will sink down to single-digit values, meaning the air will be very dry. 

Those conditions compound widespread warmth across the central and eastern U.S. on Thursday, with temperatures forecast to be between 15 and 25 degrees above average for this time of year, depending on the place.

The resulting fire danger is considered extreme because wildfires can grow quickly and spread uncontrollably over dry, arid land if they do develop.

Wildfire risks surfaced in central states as more than 100 wildfires were already burning in Florida  and Georgia, destroying homes, prompting burn bans and forcing hundreds of evacuations. The blazes come as weather data show drought conditions in the U.S. reached record heights, and meteorologists warned of the potential for a more destructive oncoming wildfire season.