DermUV
Monthly UV Index
Flagstaff, AZ
Monthly UV Index in Flagstaff, AZ
Average UV in Flagstaff 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.
Flagstaff UV Index by Month
Average UV in Flagstaff 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 Flagstaff is lowest during Jan, Dec.
| Month | Avg UV | Risk |
|---|---|---|
| Jan | 6.2 | High |
| Feb | 7.9 | High |
| Mar | 9.9 | Very High |
| Apr | 11.7 | Extreme |
| May | 12.7 | Extreme |
| Jun | 13.1 | Extreme |
| Jul | 12.9 | Extreme |
| Aug | 12.2 | Extreme |
| Sep | 10.7 | Very High |
| Oct | 8.6 | Very High |
| Nov | 6.7 | High |
| Dec | 5.8 | Moderate |
Highest UV Months in Flagstaff
Peak monthly UV reaches about 13.1 in May, Jun, Jul. That is the period when unprotected skin burns fastest, especially near solar noon. Check the live UV index in Flagstaff, AZ 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 Flagstaff
Monthly UV is lowest in Jan, Dec, around 5.8 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 Flagstaff
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 Flagstaff UV Pages
What to do with this UV Index Flagstaff, AZ data
Sunscreen labels are tested at 2 mg/cm². Typical real-world application is closer to half that, so DermUV assumes about half the labelled SPF when it estimates protected time.
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.
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.
Reapplication matters more than the SPF number. Reapply roughly every two hours outdoors and immediately after swimming, heavy sweating, or towelling, regardless of what the bottle claims.
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.
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
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DermUV forecast values come from Open-Meteo UV data (CC BY 4.0) and are refreshed throughout the day.