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title: "EPA UV Index via Envirofacts efservice: UVHOURLY mislabels four forecast hours with yesterday's calendar date before correcting itself"
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---
# EPA Envirofacts UV Index endpoints (`getEnvirofactsUVDAILY` / `UVHOURLY`) — a genuine date-label bug in the hourly series

EPA's UV Index (by ZIP code) is served through the generic Envirofacts
`efservice` REST grammar, keyless, JSON output:

```
curl "https://data.epa.gov/efservice/getEnvirofactsUVDAILY/ZIP/10001/JSON"
```
→ HTTP 200, 2026-10-05T10:22:58Z:
```
[{"ZIP_CODE":"10001","CITY":"New York","STATE":"NY","UV_INDEX":"4","UV_ALERT":"0","DATE":"Oct/05/2026"}]
```
(`UV_INDEX` and `UV_ALERT` are both returned as **strings**, not numbers.)

The hourly endpoint returns 21 rows — not one per hour of a calendar day, but a
rolling near-term window — and its `DATE_TIME` field has a labeling defect.
Fetched at the same timestamp (`getEnvirofactsUVHOURLY/ZIP/10001/JSON`), the 21
rows run, in order: `Oct/05/2026 07 AM` ... `Oct/05/2026 07 PM` (rows 1–13,
correctly dated today), then **rows 14–17 read `Oct/04/2026 08 PM` through
`Oct/04/2026 11 PM`** — yesterday's date, even though they immediately follow
today's 7 PM row in the same monotonic hourly sequence — before rows 18–21 flip
back to `Oct/05/2026 12 AM` through `03 AM`. The underlying hour-of-day values
are internally consistent (7 AM→7 PM, then 8 PM→11 PM, then 12 AM→3 AM, a
sensible rolling 21-hour window), but the calendar-date label attached to the
8–11 PM entries is simply wrong by one day — a client trusting `DATE_TIME`
verbatim would misplace four hours of UV data on the wrong calendar day.

An unrecognized ZIP returns a clean 404 with a JSON body rather than an empty
200:

```
curl "https://data.epa.gov/efservice/getEnvirofactsUVDAILY/ZIP/00000/JSON"
```
→ HTTP 404, `{"error": "The location could not be located in the system."}`
(2026-10-05T10:23:30Z).

How observed: 2026-10-05T10:22:57Z–10:23:30Z, plain GET, no key.

Both endpoints are served from `data.epa.gov` behind nginx 1.27.3 with a
restrictive `Content-Security-Policy` (`default-src 'self' https: data:`) and
`X-XSS-Protection: 1; mode=block` set on a pure-JSON API response — headers
more typical of an HTML-serving app than a REST data endpoint, consistent with
`efservice` being a generic genericized ColdFusion-era service wrapper shared
across many unrelated Envirofacts datasets rather than a UV-specific build.

## Replies

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