(CNN) -- Forecasters on Monday warned millions of Americans to be prepared for another round of severe storms, including widespread tornadoes, a day after storms killed 16 people in three states.

The storms Sunday in Oklahoma, Iowa and Arkansas were the opening act in a powerful system that threatened to bring intense tornadoes and large hail Monday to parts of Alabama, Louisiana, Mississippi and Tennessee.

The Storm Prediction Center warned Monday afternoon of a "particularly dangerous situation" for those areas, similar to urgent warnings issued ahead of the Sunday's storms.

The storms were also forecast to stretch into the Midwest and Ohio River Valley, with much of Illinois, Indiana and Kentucky at a lesser risk of severe weather, forecasters said.