updated 5/12/2010 1:21:12 PM ET 2010-05-12T17:21:12

Residents in the southern Plains still reeling from a deadly tornado outbreak that forecasters had warned about for days were bracing for even more storms.

The National Weather Service said a storm system that was expected to move into the Plains and parts of the Midwest on Wednesday could bring more thunderstorms, heavy rain and possibly even tornadoes to a region that saw deadly twisters two days earlier.

Scientists were able to predict almost to the hour when Monday's twisters might strike, thanks to technological advances, particularly the use of supercomputers that can crunch vast amounts of atmospheric data.

The line of storms may have spawned as many as 19 tornadoes as it marched through central Kansas and into Oklahoma, leveling houses, flipping cars and dropping hail as big as softballs. Two people were killed and dozens more injured.

"What is disheartening is to tell people for a week that something is going to happen, get warnings out and still have people lose their lives," said Dick Elder, chief meteorologist with the National Weather Service in Wichita.

Since the storms, families have been picking through broken furniture and dented appliances outside their shattered homes. Garbage trucks have been scooping up mattresses and other debris.

"We're just worried about the next round coming through and water damage," said Sara Hasley, of Tecumseh, who emerged from a neighbor's storm cellar after the violent weather earlier this week to find shingles missing from her mother's roof.

State officials, meanwhile, revised the death toll from that storm system from five to two after discovering three critically injured Cleveland County children had survived. A miscommunication occurred when relatives called a hospital to check on the children, who had been transferred, and state officials were later told they had died, said Oklahoma Department of Emergency Management spokeswoman Michelann Ooten.

The children's 27-year-old mother was killed, as was a 41-year-old man who died in southeast Oklahoma City.

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