Severe thunderstorms and tornado watches are in place on Tuesday, with 40 million Americans on alert for strong winds, large hail and flash flooding.

Those with outdoor plans this Memorial Day weekend should have ways to receive warnings and stay tuned to changing weather conditions.

New guidance suggests most early afternoon development could happen north, with increased coverage by the evening. Most storms should be over southeast areas by 8 p.m.

Tornado sirens are usually the telltale sign to take cover during severe weather. In St. Louis, tornado sirens didn't go off during a deadly tornado.

Millions from Oklahoma, Kansas, Missouri and Nebraska are under severe weather threat. In St. Louis, Missouri, families are cleaning up after devastating storms in recent days. NBC News’ Shaquille Brewster is there.

WICHITA, Kan. (KWCH) - Storm Team 12 Weather Alert continues for the threat of some hail and high winds for south central and eastern Kansas. The potential of severe storms should end shortly after midnight, but some scattered storms may linger for the area even early Tuesday.

Severe weather conditions are possible in areas of Colorado’s Eastern Plains on Friday evening, with the potential of bringing up to apple-sized hail, wind gusts and tornadoes.

The IMD has issued red and orange alerts for Maharashtra and Goa as a depression forms over the Arabian Sea. Heavy rain, gusty winds, and traffic disruptions are expected.