A baroclinic leaf is coming our way with a deluge of soaking rain, according to the National Weather Service in Seattle.

What is a baroclinic leaf, you say? It’s a rapidly developing region of thermal contrast in the atmosphere where a frontal system is forming. And it’s not that common, weather service meteorologists say. The leaf shape is created when air from the low level on the warm side of a cold front rises.

As the weather system develops, the shape will change to more of a “comma,” according to the weather service.

“It’s developing way off shore and its shape is an indicator it’s developing rapidly,” said Dana Felton, a meteorologist with the weather service. “You don’t want to see a baroclinic leaf develop right off your coast because it has the potential to be a strong storm that could produce widespread damaging winds.”

The baroclinic leaf heading toward the Seattle area was formed south of the Aleutian Islands, he said. Soaking rain will arrive in the Seattle area by Thursday, when the baroclinic leaf will be upon us, according to meteorologists.

But stay tuned. An upper-level ridge will bring a return of the sun on Friday, with temperatures near 60 on Saturday and a sunny 70 degrees on Sunday and Monday.

By Tuesday, the rain is expected to return.