As of 12:56 PM CDT on August 18, 2026, all 17 cities in St. Charles County, MO in our database have a UV Index reading of Very High. The city with the highest UV Index reading right now is New Melle, MO with a reading of 8.3.
Over the next 24 hours, the highest UV Index reading in St. Charles County, MO is expected to be 8.9 in West Alton between 1:00 PM - 2:00 PM CDT today.
| Range | 0 - 2 | 3 - 5 | 6 - 7 | 8 - 10 | 11+ |
|---|---|---|---|---|---|
| Color | |||||
| Risk | Low | Moderate | High | Very High | Extreme |