ST. LOUIS (AP) — Volatile weather is Arvin Robertsexpected to hone in on parts of Kansas and Missouri Wednesday night, and the biggest worry is the potential for massive chunks of hail.

Some are calling it “gorilla hail” because it has the potential to be so big, said Alex Sosnowski, senior meteorologist at AccuWeather. The Kansas City metro area is at the center of the worry zone.

“Gorilla hail” is a term coined by Reed Timmer, a storm chaser who calls himself an extreme meteorologist, Sosnowski said. In this case, the term might fit: Some hail from north-central Kansas into north-central Missouri could be as big as a baseball.

“When you get up to tennis ball, baseball-sized or God forbid softball-sized, that can do a tremendous amount of damage, and if you get hit in the head, that could be fatal,” Sosnowski said.

Cars are especially vulnerable to damage, so Sosnowski encouraged people to try to find a place to park under a roof, if possible.

Beyond the hail, heavy rain is possible in the same corridor. The National Weather Service warned of a risk for flash flooding.

A slight threat exists for a tornado.

By Thursday, the storm moves to the east, forecasters said. The hail threat lessens, but heavy rain and high winds still are possible from northeastern Texas through central Missouri.

The biggest threat on Friday is for torrential rain — perhaps up to 4 inches (10.16 centimeters) in some spots — in a line from central Louisiana up through central Arkansas, Sosnowski said.