In addition to possible twisters, the storms are also expected to produce large hail, flooding rain and gusts strong enough to uproot trees and snap power lines. Forecasters expect weather conditions to worsen Wednesday and continue overnight through Thursday as storms increase in size.

The worst conditions are likely to affect the central Plains region, including southeastern Nebraska, northwestern Missouri, central and eastern Kansas and parts of northeastern Oklahoma, according to the National Weather Service. The weather service said the storms bring an increased threat of EF2 to EF5 tornadoes, which could produce winds as low as 110 mph and as high as 200 mph.

Forecasters say the storms will form as a cold front moving in from the west collides with warm, moist air moving northward from the Gulf of Mexico. Meteorologists are warning millions of residents in the central US to charge their phones and monitor their devices for emergency alerts.