A spring snowstorm along the foothills of the Rocky Mountains in Colorado and Wyoming is ramping up, with heavy snowfall bringing traffic closures and scattered power outages.

The National Weather Service in Wyoming says up to 20 inches of snow is expected to fall through Sunday, posing a threat to livestock.

In Colorado, heavy snow was falling on Saturday across most of the state, with about 2 feet of snow in some areas.

Airlines at Denver International Airport canceled about 840 flights.

Meanwhile, heavy rain on the Eastern Plains prompted flood warnings in eastern Colorado, but no severe damage has been reported.

Forecasters in Oklahoma are warning of severe thunderstorms in western Oklahoma and northwest Texas, with large hail and damaging wind gusts. They also warned of possible flooding.

Organizers of a marijuana rally in Denver have canceled their scheduled festival to mark the April 20 pot holiday because of the storm.

The Denver rally leadership team said on its Facebook page that Saturday's rally will be rescheduled due to weather and other issues.