A blast of cold Canadian air was expected to push through Nevada, Utah, Wyoming and Colorado, bringing with it at least 6 inches (15 cm) of snow and winds gusts of 35 mph (56 kph) throughout the day and into Wednesday, the National Weather Service (NWS) said.
The cold front follows a long spell of hot, dry weather that plagued the region for the last two months.
At midday on Tuesday, the temperature dipped to 35 degrees Fahrenheit in Denver, where snow was falling with gusty winds, a day after Colorado's capital reached 93 degrees, the 73rd day of temperatures above 90 degrees, tying the city's record.
Since forecasters began keeping records about 150 years ago, a one-day change in temperature of 55 degrees or more has occurred two dozen times in Denver, according to the NWS.
The NWS warned the storm could produce freezing rains and white-out conditions, while downing trees and power lines, potentially causing electricity outages.
The precipitation was welcome news to crews battling Colorado wildfires, particularly the 102,000-acre Cameron Peak blaze in the Arapaho and Roosevelt National Forests.
The cold front will push east into the Southern Plains and central United States, where heavy rain and thunderstorms are in the forecast through the week.