# Chicago, IL UV Index Today — hourly UV forecast

> Source: https://breathecheck.com/uv-index/us/illinois/chicago/
> UV index in Chicago, IL right now, today's peak and the hour it arrives, on the EPA scale. Modelled data, labelled as modelled.

# Chicago, IL UV Index Today

Modelled for 14 Sep 2026, 22:00 UTC · GMT-5

## What is the UV index in Chicago right now?

0.8 Low

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

Today's peak is 6 ( High ) at about 1pm local time.

## When is UV strongest in Chicago today?

UV in Chicago peaks at 6 (High) around 1pm local time (GMT-5). It stays at 6 or above — the high band — for 1 hour, roughly 1pm to 2pm. UV is 3 or above for 6 hours.

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

## Chicago today, in numbers

- **Latitude**: 41.9°N — 33 of 121 from the north

- **Today's peak**: 6 (High) — 81 of 121 nationally

- **Peak arrives**: 1pm local (GMT-5)

- **At or above 6**: 1 hour, 1pm to 2pm

- **At or above 3**: 6 hours, 10am to 4pm

The window from 1pm to 2pm is the practical answer for Chicago 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 →

## The lake clears summer sky and builds winter cloud

Lake Michigan does two opposite things to Chicago’s sky, on opposite halves of the year. In summer the water is colder than the land, and the lake breeze pushes that cool, stable air a few miles inland. Stable air resists the rising motion that builds afternoon cumulus, so on a lake-breeze day the clearing shows up as a boundary running roughly parallel to the shore, the lakefront under open sky and ground a few miles west under cloud.

Late fall and early winter reverse the temperature difference. The lake is then warmer than the air crossing it and feeds moisture into it. The Illinois State Climatologist’s account of Chicago’s climate has the lake increasing cloudiness over the area and enhancing winter precipitation through lake-effect snow, which reaches the city on winds out of the north or northeast rather than the prevailing westerlies. Those are the weeks when the sun has least to give anyway.

Sun angle sets the outer limit either way. At 41.9°N the noon sun reaches about 25 degrees at the December solstice and roughly 72 in late June, a swing of some 47 degrees. The lake widens both ends of it. It takes cloud off the shoreline in the season when the sun is already high, and puts cloud back in the season when the sun has nothing left. Most of the country gets those two effects from unrelated weather. Here they come from the same body of water, six months apart.

## 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.

## What does Chicago’s UV index mean today?

0.8 is Low. EPA describes low UV as needing no protection for most people. Today Chicago 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 Chicago 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 Chicago

**What is the UV index in Chicago today?**

0.8 right now (Low), peaking at 6 around 1pm local time. UV stays at 6 or above for 1 hour, from about 1pm to 2pm. This is a modelled value, not a ground measurement.

**When is UV strongest in Chicago 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.

## Related

On this page

Air quality alerts

We alert on AQI, not UV — UV is predictable from the calendar, air quality is not.

Updated 14 Sep 2026, 22:00 UTC