Temperatures in Denver hit 91 degrees on Labor Day, but the Rockies are seeing quite different conditions less than 24 hours later.
The Denver metro area is now in the mid-30s, with snow in the forecast.
Heavy snow was already falling Tuesday morning along Colorado State Route 127 just south of the Wyoming border.
The major storm system will bring freezing temperatures, measurable snow, and strong winds. Some of the highest peaks could receive one to two feet of snow.
Winter storm warnings stretch from Montana down into Colorado as a result of the system.
Snow ends by early Wednesday, with temperatures moderating through Friday across the area.
Heavy rain and thunderstorms will also be the focus along the same cold front, carving across the Central U.S. the next few days.
Meanwhile, along the West Coast, extreme heat continues for California, the Great Basin and the Southwest throughout the day.
Excessive Heat Warnings and Fire Weather Watches remain in effect.
The strong winds have also caused critical fire danger across the region.
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Temperatures in the 90s and 100s continue across the region, keeping fire weather conditions critical across these areas through midweek.
California has seen 900 wildfires since Aug. 15, many of them started by an intense series of thousands of lightning strikes in mid-August. There have been at least eight confirmed fire deaths and more than 3,300 structures destroyed.
One blaze was started by a gender-reveal party, officials revealed late Sunday.
Smoke from fires will also spread across the Southern U.S. this week.
Fox News' Brandon Noriega contributed to this report.