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St. Louis, MO UV Index Today

Modelled for · GMT-5

What is the UV index in St. Louis right now?

1.2 Low

EPA describes low UV as needing no protection for most people.

Today's peak is 7.3 (High) at about 1pm local time.

When is UV strongest in St. Louis today?

UV in St. Louis peaks at 7.3 (High) around 1pm local time (GMT-5). It stays at 6 or above — the high band — for 3 hours, roughly 12pm to 3pm. UV is 3 or above for 6 hours.

Local time, midnight to midnight. Bar colour is the EPA UV band, never restyled.

St. Louis today, in numbers

Latitude
38.6°N — 67 of 121 from the north
Today's peak
7.3 (High) — 49 of 121 nationally
Peak arrives
1pm local (GMT-5)
At or above 6
3 hours, 12pm to 3pm
At or above 3
6 hours, 10am to 4pm

The window from 12pm to 3pm is the practical answer for St. Louis today. Nationally today the spread runs 11.4 in Hilo (20°N) to 1.3 in Fargo (47°N). Why latitude and the clock decide this →

Gulf Moisture Decides The Summer Sky

Gulf moisture runs north up the Mississippi valley through June, July and August, and it is the input that actually moves the numbers here. Water vapor itself does little to filter ultraviolet, but it feeds the haze and the afternoon cumulus that do, and it makes cloud a far less predictable variable than in a dry western city where a clear July morning is close to a given. The same calendar date can deliver two very different readings a week apart, and the difference is atmospheric rather than seasonal.

The geometry, by contrast, is fixed. At 38.63°N the noon sun reaches close to 75 degrees above the horizon at the June solstice and drops to roughly 28 in late December. That is the same arithmetic as Colorado Springs, two tenths of a degree north. Both cities take the same sun at the same hour on the same date, and St. Louis takes it through 5,500 more feet of atmosphere.

Ground level contributes nothing to any of it. The city stands about 466 feet above sea level on flat river land, downstream of the point where the Missouri joins the Mississippi, and there is no altitude term here worth writing down.

Nearest metros we model

UV changes with latitude, not with a city boundary, so a neighbour a hundred miles north reads differently for a reason.

Indianapolis, IN 230 mi · 39.8°N peak 6.7 Kansas City, MO 238 mi · 39.1°N peak 7.4 Memphis, TN 241 mi · 35.1°N peak 8

What does St. Louis’s UV index mean today?

1.2 is Low. EPA describes low UV as needing no protection for most people. Today St. Louis also reaches High at its peak — a different band from the one it is in right now, which is why the hour matters as much as the day.

The scale is open-ended: 11 is where the named bands stop, not the maximum. All five bands, with the EPA guidance for each →

Modelled, not measured

The UV figures for St. Louis are computed by the Copernicus atmosphere model, not read off an instrument here — unlike the AQI on our air-quality pages, which comes from a regulatory monitor. Cloud is where a UV model is weakest. What that means in practice →

Questions about UV in St. Louis

What is the UV index in St. Louis today?

1.2 right now (Low), peaking at 7.3 around 1pm local time. UV stays at 6 or above for 3 hours, from about 12pm to 3pm. This is a modelled value, not a ground measurement.

When is UV strongest in St. Louis today?

Around 1pm local time (GMT-5), not at noon — solar noon drifts across a timezone and daylight saving moves it later on the clock.

Is this measured or modelled?

Modelled. The figures come from the Copernicus atmosphere model via Open-Meteo, unlike the AQI on our air-quality pages, which is read from an EPA regulatory monitor. Cloud cover is where a UV model is weakest.

St. Louis air qualityThe AQI, from a regulatory monitor rather than a model UV across the USWhere St. Louis sits against every metro we track

Updated