Colorado weather can change drastically over a day, and can see all weather conditions throughout the year. It's not uncommon to have wide temperature swings from one day to the next (40 degrees F!) or even in a summer day (a thunderstorm can drop the temperature30 degrees in 15 minutes). Colorado is a high desert, and typically sees less moisture as a result. Also, it's a little known secret that Colorado has more sunny days per year than Florida.

Typically, the lowest temperatures in the winter are 0F (usually 10-20F) and highest in the summer are 110F (usually 90-100F). The mountain areas are usually 10 degrees F colder (at least) than the Denver/Front Range area, and the Southern part of the state is typically warmer than the Northern half. Humidity is typically less than 30%, further showing this is a desert plains area.

It has snowed each month of the year in Colorado, but the snow is mainly during the months of late October - late April. Snow is usually heavier and wetter (more moisture) in the spring time than winter. The mountains receive more snow and it sticks around longer than Denver/Front Range area. Some mountain roads going over passes close during the winter, and others close temporarily. Most will reopen late May (Memorial Day), but it depends on the snow pack. Trail Ridge Road in Rocky Mountain National Park is one of these roads. Denver averages less than 1 major snowstorm per season; meaning several feet of snow in a few days shutting down roads, the airport and businesses.

During the summer, along the Front Range, it will get hot causing thunderstorms and hail to develop in the afternoon moving out East. Thunderstorms, lightning, hail, and sometimes tornado warnings and watches are quite common and frequent at this time. Less common in the mountains, but they can still have thunderstorms and hail.

Weather typically comes from the West/North West. Along the Front Range, you can look towards the mountains to see what weather is coming.

Rafting season is May - August, with peak runoff in mid-June. The best snow conditions are late-December to early-March. Ski areas typically close mid to late April; however, A-Basin is open until June and extends later each year it seems. You can play golf all year long, depending on the snow and weather. April - October are better golfing months with May - September the prime times.

It also can be very windy in Colorado, with sustained winds up to 40MPH and gusts exceeding 100MPH. This is usually preceding a storm front or weather change,  and for a day or two maximum. Driving along certain roads can be dangerous during these conditions and roads can be closed because of the winds.

BEST TIMES TO TRAVEL 

Summer-

The big tourist crowds appear from late June until early August. The best time to experience a Colorado summer is from about August 15th until the Labor Day weekend. The families have returned home to shop for school and the seniors like to wait until September to travel. You will generally have trails that are deserted and hotels that are 1/4 full. Look also for airfare discounts during this period as this is typically a slow time for air travel. Even the locals have to deal with school so attractions are slower at this time than in mid-summer. Second best time for summer travel is From Memorial Day Weekend until about June 20th for most of the same reasons. The only downside is that June tends to be a wetter and cooler month than August. Much of the snow melt is still occurring, so some high mountain trails might still be unpassable and the afternoons and nights have more of a "bite".

Winter- 

It is assumed that if one is coming in winter then snow is expected.  The snow generally doesn't start to really fly until January. Right after New Year until late January is a great time to have the mountain runs to yourself, but, in general, the snowpack doesn't get truly great until February. If you want  to avoid crowds, February and March are not your months, although early February can be less crowded. The spring skiing is delightful in April and the first two weeks of this month can be perfect: beautifully warm days and plenty of snow. Just make sure you don't rush out the door early unless there is fresh powder; the snowpack can get hard and fast (until mid-morning) from the warm days . Most resorts offer big discounts on lodging as well as lift tickets to squeeze the last few dollars out of the season.