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San Antonio, TX UV Index Today

Modelled for · GMT-5

What is the UV index in San Antonio right now?

2.3 Low

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

Today's peak is 8.7 (Very High) at about 1pm local time.

When is UV strongest in San Antonio today?

UV in San Antonio peaks at 8.7 (Very High) around 1pm local time (GMT-5). It stays at 6 or above — the high band — for 4 hours, roughly 12pm to 4pm. UV is 3 or above for 7 hours.

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

San Antonio today, in numbers

Latitude
29.4°N — 116 of 121 from the north
Today's peak
8.7 (Very High) — 12 of 121 nationally
Peak arrives
1pm local (GMT-5)
At or above 6
4 hours, 12pm to 4pm
At or above 3
7 hours, 10am to 5pm

The window from 12pm to 4pm is the practical answer for San Antonio 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 →

Near-overhead sun and the latest clock noon

Of the ten most populous cities in the country, San Antonio is the farthest south. At roughly 29.4°N it sits about a third of a degree below Houston and well below Phoenix, Los Angeles and San Diego. That position does two specific things to the index.

The first is the height of the summer sun. At this latitude the solstice sun reaches about 84 degrees above the horizon at solar noon, within six degrees of straight overhead, so the path the light takes through the atmosphere is near its minimum. The second is the winter floor. Midday sun around the December solstice still stands about 37 degrees up, which is why the index here does not collapse the way it does across the northern half of the country.

Longitude adds a wrinkle. At 98.5°W, San Antonio is the westernmost of the four largest Texas metros, and solar noon lands near 1:35 p.m. in daylight time, give or take the quarter hour the equation of time moves it through the year. That is later on the clock than in Houston, Dallas or Austin, and it means the day’s highest reading is an early-afternoon event on a watch rather than a midday one.

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.

Austin, TX 74 mi · 30.3°N peak 8.7 Houston, TX 189 mi · 29.8°N peak 8.6 Fort Worth, TX 239 mi · 32.7°N peak 8.7

What does San Antonio’s UV index mean today?

2.3 is Low. EPA describes low UV as needing no protection for most people. Today San Antonio also reaches Very 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 San Antonio 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 San Antonio

What is the UV index in San Antonio today?

2.3 right now (Low), peaking at 8.7 around 1pm local time. UV stays at 6 or above for 4 hours, from about 12pm to 4pm. This is a modelled value, not a ground measurement.

When is UV strongest in San Antonio 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.

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

Updated