-999 degrees tempC

[EricThePinecone]

Report for Ludlow, GB, 2026-08-04 shows tempC to be -999, and tempF to be -1767, at 2100h.

Report was fetched at 21:31 GMT. The anomalous figures appear in both the JSON report and the HTML version at wttr.in/Ludlow

Oddly, a report fetched earlier in the day (at roughly 04:00 GMT) does not contain these anomalies.

Did try checking if the same error was present on worldweatheronline for Ludlow, but it wasn't.

Have attached both the odd JSON report, and the one that doesn't include the error, as well as a screenshot of the webpage.

wttr_2026-08-04T0400.json
wttr_2026-08-04T2130.json

[eirik-rune]

Not reproducing right now (2026-08-06 07:38 UTC), including at the exact coordinates from the report:

/Ludlow?format=j1          sentinels 0
/52.366,-2.714?format=j1   sentinels 0
/London  /Oymyakon  /Reykjavik   sentinels 0

The scanner walks the whole j1 document and flags any leaf equal to -999 or -1767. I calibrated it before trusting the zero: injecting -999/-1767 into one hourly slot of a real response makes it report 2, the untouched response reports 0. So the zero is a real absence, not a broken query. Ludlow's 2100h slot currently reads tempC 13. Consistent with the reporter's own note that an earlier fetch that day was clean — this looks transient, i.e. a bad value passing through rather than a stable bug you can catch with a fixed test.

One thing that might narrow the fix. I checked whether tempF could be derived from tempC, in which case guarding one field would cover both. It cannot:

48 real (C,F) pairs from one j1 response (tempC/tempF and FeelsLikeC/FeelsLikeF)
round(C*9/5+32)   34/48
floor(C*9/5+32)   23/48
ceil(C*9/5+32)    25/48
int(C*9/5)+32     23/48
deviation F - (C*9/5+32) ranges -1.20 .. 0.80, 3 of 48 outside +/-1

No single rule fits, and the spread is wider than one rounding step, so the two fields arrive independently rather than one being computed from the other. -1767 is simply what -999 C looks like when the same sentinel is converted upstream, not evidence that the conversion happened in wttr.in.

Practical consequence: a sanity check that rejects sentinel temperatures needs to sit on both C and F (and probably on FeelsLike* too), at ingest. -999 is the classic "no data" marker from weather backends, so clamping or dropping the slot is likely safer than trusting it through.

Plain curl, no key needed, if you want to re-run any of it.