Texas fires happen in the winter. Just never at this scale before.

Dozens of wildfires are tearing through the Texas Panhandle and Oklahoma after igniting earlier this week, including what’s now the second-largest wildfire in US history.

Dubbed the Smokehouse Creek Fire, the massive blaze, the largest in Texas’s history, has engulfed more than 1.1 million acres and was 3 percent contained as of Thursday morning, spurred by dry weather and high winds. The fire has killed at least one person, triggered evacuations, and shrouded a swath of the country in smoke. The encroaching flames forced the Pantex nuclear weapons manufacturing plant in Amarillo to shut down and sent cattle fleeing.

Texas Gov. Greg Abbott this week issued a disaster declaration for 60 counties in response to the fires. The region is expected to get some cooler temperatures, rain, and snow on Thursday and Friday, but forecasters warn that dangerous fire conditions will pick up again through the weekend.

Wildfires are not unusual in Texas and Oklahoma, even at this time of year, but the speed and scale of the current blazes did surprise researchers.

“We were monitoring that area for increased wildfire activity, but in terms of the magnitude and the outcome, what occurred outperformed our expectations,” said Luke Kanclerz, head of the predictive services department at the Texas A&M Forest Service. “We flipped the switch very quickly.”

Though recent weather is playing a key role in the Texas and Oklahoma wildfires, including a sudden burst of extreme heat this month, the foundations for the conflagrations were laid almost a year ago. There are three key factors that have made the situation so severe:

A wet spring in 2023 …

Following a severe drought in 2022, the Texas Panhandle was soaked last spring. “We had a copious amount of rainfall, above normal, 300 to 400 percent of normal rainfall in May and June in the Texas Panhandle,” Kanclerz said. “That rainfall produced a very robust grass crop across the region.”

… followed by a really hot summer …

The region was then baked in an intense, early-season heat wave followed by more bouts of scorching, record-breaking temperatures throughout the summer. Like much of the country, the heat in the southern Great Plains states was exacerbated by a strong El Niño. This phenomenon typically raises global temperatures, but across the southern US, it also shifts atmospheric air currents, and last year, these currents pinned hot air over the South for weeks at a time. Hot, dry air dried out the grasses that are fueling the current fires.

… over a complex landscape.

The region tends to be flat, but the Canadian River basin spanning Texas and Oklahoma has complex, rocky terrain, making it hard to monitor, access, and contain a fire once it has ignited. “Where the fires became established in the river drainages, they were able to burn freely with a lot of open range and become established very quickly,” Kanclerz said.

Investigators are still probing what ignited the fires, but the majority of wildfires in the region are ignited by people, though often by accident. While global average temperatures are rising, it’s not clear how climate change might be affecting the Texas and Oklahoma fires. Kanclerz noted that the region’s fires tend to vary drastically between seasons so it’s hard to pick up any trends.

But one of the strongest signals of climate change is warmer winters, and the heat waves across the South in the past few weeks line up with what scientists expect will happen as temperatures continue to rise.