DermUV
Monthly UV Index
St. Louis, MO
Monthly UV Index in St. Louis, MO
Average UV in St. Louis 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.
St. Louis UV Index by Month
Average UV in St. Louis 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 St. Louis is lowest during Jan, Dec.
| Month | Avg UV | Risk |
|---|---|---|
| Jan | 4.7 | Moderate |
| Feb | 6.1 | High |
| Mar | 7.9 | High |
| Apr | 9.6 | Very High |
| May | 10.6 | Very High |
| Jun | 11.0 | Extreme |
| Jul | 10.8 | Very High |
| Aug | 10.1 | Very High |
| Sep | 8.7 | Very High |
| Oct | 6.8 | High |
| Nov | 5.1 | Moderate |
| Dec | 4.3 | Moderate |
Highest UV Months in St. Louis
Peak monthly UV reaches about 11.0 in May, Jun, Jul. That is the period when unprotected skin burns fastest, especially near solar noon. Check the live UV index in St. Louis, MO 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 St. Louis
Monthly UV is lowest in Jan, Dec, around 4.3 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 St. Louis
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 St. Louis UV Pages
Context behind UV Index St. Louis, MO
Burn-time figures come from minimal erythemal dose (MED) values published for each Fitzpatrick skin type, divided by the erythemal irradiance at a given UV index. Personal MED varies by roughly 20 percent, so treat every number as a planning range.
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.
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.
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.
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.
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 st. louis, mo, from UV-scale reference material to definitions and city forecasts.
- UV and sunscreen glossary
- Minimal erythemal dose
- UV Index 8 explained
- UVA definition
- What UV index 8 means
- What UV index 3 means
- BROAD-SPECTRUM definition
DermUV forecast values come from Open-Meteo UV data (CC BY 4.0) and are refreshed throughout the day.