A powerful spring snow storm was expected over the next three days to blanket parts of the U.S. Rockies and central High Plains where forecasters warned of whiteout conditions, power outages and avalanches.

The National Weather Service (NWS) issued blizzard warnings for parts of Wyoming and western Nebraska, where quickly accumulating snowfall of up to 2 feet (61 cm) and fierce winds reaching 65 miles (105 km) per hour could cause dangerous conditions from Saturday through Monday.

The weather service told travelers who must be on the road to carry emergency supplies and flashlights. It also warned that strong winds and the heavy snow could cause extensive damage to trees and power lines.

“We’re preparing for a potentially historic winter storm to impact Southeast Wyoming,” Wyoming Governor Mark Gordon said on Twitter. “The best option is to stay off the roads this weekend.”

To the south in Colorado, conditions were forecast to deteriorate throughout the day on Saturday. The I-25 urban corridor, where five million people live in cities such as Denver, was expected to get 2 feet of snow and 35 mph winds throughout the weekend.

In Denver, rain turned to snow late Saturday morning as temperatures dropped to near freezing. A drier air pattern moving over the city in the afternoon temporarily slowed the rate of snowfall, the NWS said on Twitter.

“However, more intense snow will return by late afternoon/early evening and into Sunday,” the weather service said.

At Denver International Airport, 1,979 weekend flights in and out of the nation’s fifth busiest airport were cancelled ahead of the storm, according to aviation tracking web site Flight Aware.

Utility company Xcel Energy said this week that it was “ramping up the number of crews” to respond to any possible power outages caused by the heavy, wet snow.

The NWS warned travelers and skiers in higher elevations that avalanches could be easily triggered as snow totals could rapidly accumulate, while Colorado Governor Jared Polis activated the state’s National Guard to respond to search and rescue requests over the weekend.