Colorado
In my opinion, Colorado has just about the best climate in the country (if you like four seasons). People say Denver has 300 sunny days a year. Well, myth aside, the reality is closer to 300 days where the sun shines at least part of the day. Summers are hot with pleasant nights in the eastern part of the state and on the Western Slope. The mountain comminties have warm days and cool nights. The winters are cold and snowy in the mountains and the front range and western slope have a mixture of cold snowy days and a nice number of warm days. It's not uncommon to have 60 degree plus days on the eastern slope (Denver and east). The East and West slope can get some heavy snows during the winter, but it usually melts in a week or two. The bottom line, except in the mountains, it's quite possible to be able to cycle, with the right clothing, almost year-round. Having said that, any cyclist must always be prepared for sever weather and quickly changing conditions. Case in point, April and May have wild temperature swings. In the course of a day it can go from sunny and 80 down to zero and snowing. it's mid-April and a mere sixteen hours ago, I was cycling in 70-degree weather south of Denver. It's now 15 degrees outside, with six inches of new snow. Note: April and May can be cold and drippy/snowy months throughout the state.
General Thoughts
US Climate Data has a nice website at https://www.usclimatedata.com/climate/colorado/united-states/3175 that lists averages for many cities in Colorado. The key here is AVERAGES. At any time in any year, you can have huge temperature swings anywhere. It can get down to the 30's in Denver in the summer and up in the 70's in winter in the mountains.
Temperature Change: Colorado typically has a dry, very dry climate. That means that air can 1) cool off very quickly at night and 2) warm very quickly during the day. If camping, don't be surprised that you need to switch from shorts and t-shirts during the day, to heavy coats at sunset. It can easily be in the 80s or 90s during the day, but can easily cool to the 40s or lower at night. Day to night temperature changes of 30 plus degrees is very common. As noted above 60 degree 24-hr temperature changes are not unheard of.
Altitude: It's 7AM in Cedaredge, CO and a beautiful July morning. Clear, dry, and a light breeze. it's a very pleasant 52 degrees and you expect the temp to rise quickly into the 70s and hit 90 by early afternoon. You throw on some cycling shorts and a jersey, and head up an epic 4700-foot climb: The Grand Mesa. Life is good. Or is it? At this moment, are you aware that it's likely 27 degrees at the top? In general, if the weather is clear and dry, the temperature will drop 5.5 F degrees for every 1000 feet you climb. If it's foggy, raining, or snowing, the temperature drop is about 3.3 F per 1000 feet. And while it will take some time to get to the top and, as the day goes on, it will warm at the top... but it will still be some 25 to 28 degrees cooler at the top.
Humidity: Did I mention that Colorado is dry. I can't tell you the number of times the clouds build in the afternoon and you start seeing lightning, hearing thunder, and you can see veils of precipitation falling from the sky. The weird thing, standing on the ground, you stay dry. The air can be so dry, the falling precip evaporates before it falls on you and your bike. Our nice dry climate keeps you cool while riding on even the hottest days and the low dew point evaporates any sweat on your skin, acting like a swamp cooler, and keeps you cool and dry. This can be both good and bad at the same time: Nice comfortable temeratures and no humidity, but dehydration and even hypothermia in summer.
I laughed at people when I first moved out here when they told me I could become dehydrated just reading a book while sitting in the shade of a large tree. Well, I'm now a believer. Drink water and drink lots of it. If you have an adult beverage, for every beer, drink two glasses of water. For every cocktail, drink two glasses of water. Have liquids with you either in bottles on your bike or in a camel back. Don't rely in finding a place to buy hydration during a ride, as there are often times that you are very very remote.
Hypothermia in summer? I saw this firsthand one day on an organized tour. We rode up Mt Evans and then ended the day in Idaho Springs. After a long hot cry climb up Mt Evans, the weather changed quickly. I, as many on the ride, were prepared for a completely dry, hot, day. I did not have gloves, a jacket, or leg warmers with me. With lightning in the area, the tour closed the route and directed everyone to get to Idaho Springs quickly. The wind changed direction and dropped the temps from the high 70s to the 50s in a matter of seconds. With rain starting to fall behind me, I bolted, almost recklessly, downhill and made it down without a drop of rain on me and got my tent set up in record time. Within two minutes of finishing, the skies opened up and the temps were now in the 40s. When the rain stopped, I walked into the high school, and saw, literally, 40 to 50 riders on gurneys, tables, and the floor, all wrapped in thermal blankets and being attended by emergency services. The rain, wind, and low dew points combined to give rides who got wet, early hypothermia. I do not believe any of the cases were serious, but it was shocking to see how a perfect hot day could turn to hypothermia in minutes. Colorado's dry climate, low dew points, could cause hypothermia very very quickly. In the summer, always plan for late day rain and carry, at a minimum, leg and arm warmers, a helmet cover to keep you head dry, and a jacket or bag to keep your torso dry.
Sever Weather: The mid-west might be tornado alley, but Colorado is hail alley. Colorado and Wyoming are two of the most hail prone spots in the country. And, since hail is ice, it hurts when it hits you and is difficult, if not impossible to ride through in a bike. If caught in a hailstorm, take cover in a safe structure, under a bridge, or someplace covered. Also, hail is usually accompanied by lots of lightning. Stay away from trees. The good news is, you can usually see a storm approaching, so you should have time to find shelter. Hailstorms are most likely in May and June, but could happen any time.
Snow could actually happen any time of the year in the high country. We were in Estes Park one mid-June evening, after finishing a nice hot ride from Fort Collins. Our next day route brought us over Rocky Mtn National Park. A storm brought us a cold rain in the afternoon. Above 10,000 ft. Snow. Six inches of the stuff. We were ultimately bussed around the park- A major disappointment. When cycling in Colorado, expect the unexpected. Chances are your cycling trip will be warm and uneventful. Do plan on getting wet if you ride after 1 or 2PM. But, also be prepared for cold weather on hot days. We had a storm roll in out of Durango on Red Mtn pass. Not only did the storm cause a landslide that closed the road for a few hours, but everyone was soaked at the top of Red Mtn and freezing. A late day storm rolled in on a hot day over Loveland. The route stayed open, but we had several inches of slushy snow on the road. Made the downhill interesting. On a very hot day out of Crested Butte over Cottonwood pass, we had 60 MPH winds, no visibility, and the temps dropped from 80 to 39 in about 30 minutes. At the top, the rain was mixed with sleet and snow.
Monsoon Season: Colorado is known for bright sunny mornings, but those sunny days can give way to building scattered storms in the afternoon. From mid-July through August, these rain chances greatly increase as Monsoon Season has arrived. I'm not talking about endless days of torrential rain... But, after a nice sunny start, any day could result in heavy rain and lightning after 11AM in the mountains, after 2PM on the front range, and into the evening on the eastern plains. It's not every day. It's not everywhere. But, as they say, when it rains, it pours. For afternoon rides in the summer, have rain gear with you and take lightning safety seriously.
Bottom-Line
BE PREPARED AND DON'T GET CAUGHT UNPREPARED. One of the people I rode with always carried the kitchen sink with him on tours. He was always prepared but ended lugging a ton of excess weight up passes. Another person I rode with was quite the opposite and never carried jackets or gloves with him. In addition, he was a late start person. We typically broke camp 2-3 hours before he did. Needless to say, he got caught in a lot of rain and then complained about getting wet. There is a happy medium here. In Colorado summers, especially during monsoon season (July and August), the chances of morning rain are virtually 0. Afternoon storms... that's another story. In a normal year, plan on rain or cold weather if you will be riding past 2PM. It will only last an hour or two and will dry up quickly, but plan in getting wet. If riding between 6 and noon. Mornings will be cool, but the ride will be likely warm and dry. You likely won't need much spare equipment and it should be easy to get 60 to 80 miles in during the six hours in the morning. Obviously, ma nature may disagree, and bad weather can happen any time... but on average, in summer, mornings are dry, and afternoons are wet. My recommendation is always carry gloves, leg, and hand warmers. Add a jacket and helmet cover, always, for afternoon rides. If you are on the western slope, base your equipment on the daily forecast. If going over 11,000 feet and it's after 12, carry something warm and waterproof.
WHAT TO WEAR CYCLING IN COLORADO
