An incredible day of weather is unfolding across the country on Tuesday, as a major winter storm develops across the Rockies and a major wildfire threat grows hundreds of miles to the West.

Temperatures in Denver hit 91 degrees on Labor Day, but the Rockies are seeing quite different conditions less than 24 hours later.

An unusually cold air mass is rolling across the Rockies and the Great Plains today, sending temperatures plummeting 50-70 degrees colder than the last couple of days.

SEPTEMBER SNOW IN FORECAST FOR DENVER, AFTER 100-DEGREE LABOR DAY WEEKEND HEATWAVE

The Denver metro area is now in the mid-30s, with snow in the forecast.

Forecast high temperatures for Tuesday, Sept. 8, 2020.

Forecast high temperatures for Tuesday, Sept. 8, 2020. (Fox News)

Heavy snow was already falling Tuesday morning along Colorado State Route 127 just south of the Wyoming border.

Snow was falling Tuesday morning in northern Colorado as a storm system moved into the area.

Snow was falling Tuesday morning in northern Colorado as a storm system moved into the area. (Colorado Department of Transportation)

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.

The forecast to snow to develop across the region by Tuesday afternoon.

The forecast to snow to develop across the region by Tuesday afternoon. (Fox News)

Winter storm warnings stretch from Montana down into Colorado as a result of the system.

Winter storm warnings and advisories stretch through the region.

Winter storm warnings and advisories stretch through the region. (Fox News)

Snow ends by early Wednesday, with temperatures moderating through Friday across the area.

COLORADO BRACING FOR EARLY-SEASON WINTER STORM WITH UP TO A FOOT OF SNOW EXPECTED

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 wildfire danger continues out West on Tuesday.

The wildfire danger continues out West on Tuesday. (Fox News)

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.

The national forecast for Sept. 8, 2020.

The national forecast for Sept. 8, 2020. (Fox News)

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.

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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.