DermUV
Monthly UV Index
Fort Collins, CO
Monthly UV Index in Fort Collins, CO
Average UV in Fort Collins is highest during May, Jun, Jul and lowest during Jan, Dec. Use this month-by-month guide to plan sunscreen, shade, clothing, and outdoor timing.
Fort Collins UV Index by Month
Average UV in Fort Collins peaks during May, Jun, Jul, when high sun angles combine with longer days. The deceptive months are usually early spring and early fall, when air temperatures stay mild but UV climbs into the high category by mid-morning. Locals often skip sunscreen on cool, overcast days, which is exactly when UV-A continues to drive long-term skin damage. UV in Fort Collins is lowest during Jan, Dec.
| Month | Avg UV | Risk |
|---|---|---|
| Jan | 4.9 | Moderate |
| Feb | 6.5 | High |
| Mar | 8.5 | Very High |
| Apr | 10.5 | Very High |
| May | 11.7 | Extreme |
| Jun | 12.2 | Extreme |
| Jul | 12.0 | Extreme |
| Aug | 11.1 | Extreme |
| Sep | 9.4 | Very High |
| Oct | 7.2 | High |
| Nov | 5.3 | Moderate |
| Dec | 4.4 | Moderate |
Highest UV Months in Fort Collins
Peak monthly UV reaches about 12.2 in May, Jun, Jul. That is the period when unprotected skin burns fastest, especially near solar noon. Check the live UV index in Fort Collins, CO before outdoor plans because clouds, ozone, altitude, and reflection can move the real-time number above or below the monthly average.
Lowest UV Months in Fort Collins
Monthly UV is lowest in Jan, Dec, around 4.4 on this model. Lower UV does not mean zero UV. UVA can still pass through cloud and glass, and snow, water, or pale concrete can reflect UV back onto exposed skin.
Monthly Sunscreen Guidance for Fort Collins
For months that average UV 3 or higher, broad-spectrum SPF 30+, sunglasses, shade, and UPF clothing are the practical baseline. For months in the very-high or extreme range, reapply every two hours outdoors and after swimming or heavy sweat. These are educational estimates.
Related Fort Collins UV Pages
How to read this UV Index Fort Collins, CO page
The UV index is a measure of erythemal (skin-reddening) irradiance, where each whole point equals 25 mW/m² of UV energy reaching the surface. That is why burn-time estimates fall roughly by half when the index doubles.
UV strength on this page follows solar elevation, ozone thickness, cloud cover, altitude, and surface reflection. Snow can bounce back most of the UV that hits it, water and sand far less, but all of them add to the dose skin receives.
Plan outdoor blocks around the peak UV window, usually between 10am and 4pm local time. Shade, UPF fabric, a wide-brim hat, and UV-blocking sunglasses reduce dose more reliably than sunscreen alone.
Cloud cover is not protection. Thin or broken cloud can still pass most incoming UV, and light cloud edges can briefly scatter more UV toward the ground than a clear sky.
Cumulative dose drives photoaging and long-term skin damage more than any single day. Small daily exposures on commutes, walks, and driving add up across a season.
UV scale reference
The WHO scale groups UV 1-2 as low, 3-5 as moderate, 6-7 as high, 8-10 as very high, and 11 or above as extreme. Protection is recommended from UV 3 upward, and shade during the middle of the day becomes the priority from UV 8 upward.
A practical routine at moderate-to-high UV is roughly one ounce of broad-spectrum sunscreen for full-body coverage, applied 15 minutes before going out, then reapplied on schedule. Clothing, hats, and shade carry the rest of the load, especially for children and anyone with a history of easy burning.
Keep exploring DermUV
These pages give more depth around uv index fort collins, co, from UV-scale reference material to calculators and city forecasts.
- Sunburn time calculator
- UV learning center
- Vitamin D sun calculator
- SPF reapply timer
- vitamin d lesson
- What UV index 11 means
- reflection lesson
- UVB definition
- What UV index 9 means
All figures on DermUV are educational estimates built from public UV data and published dose literature. They are not personal advice.