A powerful storm making its way east from California is causing major disruptions during the year’s busiest travel weekend, as forecasters warned that intensifying snow and ice could thwart millions of people across the country hoping to get home after Thanksgiving.

The storm caused the death of at least one person in South Dakota and shut down highways in the Western U.S., stranding drivers in California and prompting authorities in Arizona to plead with travelers to wait out the weather before attempting to travel.

The storm was expected to track east through the weekend — into the Plains on Friday, the Midwest by Saturday and the Northeast on Sunday — pummeling a huge portion of the country with snow, ice or flash flooding.

The National Weather Service said travel could become impossible in some places.

The weather could be particularly disruptive on Sunday, when millions of holiday travelers head home.