Two things: Gusty winds and onshore flow.
"We had the onshore flow strengthen, the winds coming from the ocean, and that brought about the rapid spread of fire for Southern California," explained National Weather Service Meteorologist Dr. Ariel Cohen.
The onshore flow provided the last needed element for the fires to grow in size.
"What that does is it pushes the fire in there, and as that fire gets bigger and grows, the fire out ahead of it, as it's consuming fuel and burning vegetation, it starts drawing wind in from the other side," said Cal Fire Battalion Chief Jed Gaines.
The Bridge Fire grew to more than 49,000 acres Wednesday, and the windy conditions were nearly impossible to ignore for some nearby residents.
"The winds ... I don't know if it's because of the fire but the winds ... it was like real big gusts of winds," said Wrightwood resident Christine Johnson. "It was scary. When you went on the other side of town, it wasn't like that."
As fires gain strength, they become weather systems of their own, creating their own clouds and sometimes even thunderstorms.
"The fire effectively turns into a heat engine when it becomes large enough, and it actually can interact with the background environmental conditions and even change them around them to effectively behave like a thunderstorm," said Cohen.
While there was not enough moisture to generate a thunderstorm, the powerful winds and terrain have given the three fires dangerous fuel to grow fast.
"When we look at these pictures of what looks like a thunderstorm, is a sign that we have a very dangerous explosive fire," added Cohen.
California is only now heading into the teeth of the wildfire season but already has seen nearly three times as much acreage burn than during all of 2023. The White House said President Joe Biden was monitoring the wildfires in the West and urged residents to heed state and local evacuation orders.
Cooler temperatures were expected to potentially start tempering fire activity as the week progresses.
The Associated Press contributed to this report.