A "very active and complex mid-May weather pattern" is settling over states from the central United States through the Mid-Atlantic.

The National Weather Service said a “multitude of hazardous weather” would impact the U.S. over the next several days — from thunderstorms and potentially baseball-sized hail on the Plains, to heavy mountain snow in the West and dangerous heat in the South.

A series of severe thunderstorms packing high winds, hail and tornadoes will progress from the Great Lakes to the Ohio and Tennessee valleys through the end of the week, AccuWeather meteorologists warn.

Kansas and northern areas of Oklahoma have the highest 'moderate' risk with a population of nearly one million at threat from the most severe thunderstorms and tornadoes. By Tuesday, more than four million will be under the highest risk of severe storms and tornadoes across central and eastern Oklahoma and into the Ozarks.

BIRMINGHAM, Ala. ( WBRC) - Good morning and happy Monday!

Tuesday afternoon and evening brings a risk for severe storms as a cold front approaches Alabama from the north. An enhanced risk (level 3/5) for severe weather stretches across northwest Alabama. A slight risk (level 2/5) stretches across the I-20/59 corridor, followed by a marginal risk (level 1/5) across south Alabama.

Westmoore High School has rescheduled its graduation ceremony that was supposed to be held today because of the predicted severe weather.