It's best to wait until temperatures are consistently above 50 degrees before trading winter tires for all-seasons. Winter tires are made of a softer rubber that does not hold up well on hot pavement. On very warm spring days, the rubber can become quite soft – which can cause your winter tires to wear out much faster. Softer tires also create more drag and friction, requiring more power to move the vehicle, therefore decreasing fuel efficiency.
Generally in Colorado late April is a good time to take the winter tires off and get the all-seasons back on. This is typically when the chances of severe winter weather begin to diminish.