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Philadelphia, PA UV Index Today

Modelled for · GMT-4

What is the UV index in Philadelphia right now?

0.3 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 Philadelphia today?

UV in Philadelphia peaks at 6 (High) around 1pm local time (GMT-4). 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.

Philadelphia today, in numbers

Latitude
40.0°N — 54 of 121 from the north
Today's peak
6 (High) — 83 of 121 nationally
Peak arrives
1pm local (GMT-4)
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 Philadelphia 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 →

Longitude does more here than latitude

The Northeast corridor from Boston to Washington spans about three and a half degrees of latitude, which is not much sun. Philadelphia at 39.95 degrees north differs from New York and from Baltimore by under a degree of noon sun elevation on any date, so latitude is not what distinguishes it from its neighbors. Longitude is, and Philadelphia is the city sitting on the line.

It lies at 75.16 degrees west, within about ten miles of the 75th meridian that Eastern Time is defined from. Mean solar noon falls at 12:00 on standard time, or 1:00 p.m. once daylight saving is running, wandering up to about a quarter hour either side across the year as the equation of time drifts. Louisville, keeping the same clock from nearly 86 degrees west, does not reach its solar noon until close to 1:40. The World Health Organization frames peak exposure as the four-hour block centered on solar noon, and in Philadelphia that block needs no arithmetic to place: roughly 11 to 3 through the summer.

Elevation contributes nothing, the city being essentially at sea level on the tidal Delaware. That leaves cloud to do the daily work, and the sharpest readings here tend to arrive behind a cold front rather than in the middle of a humid stretch.

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.

New York, NY 80 mi · 40.7°N peak 5.9 Baltimore, MD 90 mi · 39.3°N peak 6.2 Washington, DC 124 mi · 38.9°N peak 6.3

What does Philadelphia’s UV index mean today?

0.3 is Low. EPA describes low UV as needing no protection for most people. Today Philadelphia 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 Philadelphia 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 Philadelphia

What is the UV index in Philadelphia today?

0.3 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 Philadelphia today?

Around 1pm local time (GMT-4), 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.

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

Updated