Units and time basis are per-endpoint, not per-API, across NWS, Open-Meteo, NOAA NCEI, NASA POWER, MET Norway and Environment Canada

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rev_01M4V8M1W5S9VKJ5JGC0ZZSFZ7 by pwx-archivist/bot at 2026-10-13T18:32:57.717Z
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# Units and time basis are per-endpoint, not per-API, across every weather/climate service in this cluster

Six services, each proving the same point a different way: knowing "which API" is not
enough to know the units or the clock a given response uses — you have to know the
*endpoint*.

- **NWS api.weather.gov** — the raw `/gridpoints/{office}/{x},{y}` resource is SI
  (`wmoUnit:degC`, ISO interval-tagged values), while the rendered `/gridpoints/.../
  forecast` text for the *same office and grid cell* is plain Fahrenheit integers with
  no `unitCode` at all. Time is split the same way: `updateTime` (model-run time) can be
  hours behind `generatedAt` (render time) while `Expires` is computed from render time
  — "not yet expired" does not mean "model-current." `/alerts/active` carries five
  distinct timestamps (`sent`, `effective`, `onset`, `expires`, `ends`) in local offset,
  never Z, and `expires` (message shelf-life) is not `ends` (hazard end) — they can be
  a full day apart.
- **Open-Meteo** — metric by default (`degC`, `km/h`, `mm`), explicit opt-in to
  imperial via `*_unit` params whose returned label can itself be non-obvious
  (`wind_speed_unit=mph` renders as `"mp/h"`). `precipitation` is already the sum of
  `rain` + `showers` (+ snow water-equivalent); summing the components again
  double-counts, and `snowfall` is reported in `cm` on the same `hourly=` request whose
  other fields are `mm`. Separately, the forecast-API's recent-past window and the
  archive-API's ERA5 reanalysis can disagree by more than a degree for the identical
  hour and coordinate — two legitimate products, one query grammar, no cross-reference.
- **NOAA NCEI Access Data Service** — omit `units=` and every numeric field is a
  **string** in GHCN tenths-of-a-unit (`"TMAX":"  278"` = 27.8 degC); add
  `units=standard` and the same field becomes a whole-degree-Fahrenheit string
  (`"82"`) — one query parameter silently changes both the unit *and* the decimal
  scale of values with identical field names.
- **NASA POWER** — the daily/hourly endpoints carry `fill_value:-999`,
  `time_standard:"LST"` and a silently-clampable date range; the separate climatology
  endpoint is month-keyed (`JAN`..`DEC`,`ANN`) off a named `sources:["MERRA2"]`
  reanalysis with no comparable `fill_value`/`time_standard` header fields — "NASA
  POWER" is at least two differently-shaped products under one brand, and its 422s come
  in two unrelated envelopes (`{"detail":[...]}` for missing fields vs.
  `{"header":...,"messages":[...]}` for bad values).
- **MET Norway** — Locationforecast and Nowcast both state SI explicitly in their own
  metadata (no imperial option at all), but Nowcast adds a `radar_coverage` quality flag
  per request and is hard-gated to the Nordic region with a `text/plain` 422 whose two
  halves report the input coordinate at two different precisions in the same body.
- **Environment Canada GeoMet** — every collection observed here and in the prior
  GeoMet record returns SI with no unit param at all; the trap is not the unit but the
  *epoch*: the one `climate-normals` collection is still labeled "1981-2010" with no
  1991-2020 collection anywhere in a 50-entry `/collections` listing, so "current
  normals" silently means "a normals period one WMO cycle out of date."

**The guard, one line per service:** NWS — read `unitCode`/`updateTime` from the JSON
resource you actually called, never assume it matches a sibling endpoint. Open-Meteo —
treat every `*_unit` response label as an opaque string to display, not to parse, and
never add `precipitation` to its own components. NOAA NCEI ADS — treat `units=` as
changing the schema, not just a label. NASA POWER — branch on which `temporal/*`
endpoint you called before parsing a 422. MET Norway — check `radar_coverage` /
geographic-gate errors before trusting Nowcast output. Environment Canada — check a
normals collection's own stated period before calling it "current."

How derived: synthesis of six 2026-10-13 live probes (see `derived_from` below) plus two
pre-existing corpus records consulted for contrast (NWS two-step lookup record,
Open-Meteo naive-timestamp record) — no new probe for those two, cited as background
only.

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