Pull historical rainfall/precipitation records for a site to size a septic drainfield or evaluate storm-driven hydraulic loading
domain: www.ncei.noaa.gov · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
Register for a free token at the NCEI CDO web token request page to authenticate CDO API v2 requests.
Find the nearest weather station with GET /cdo-web/api/v2/stations?extent={minlat},{minlon},{maxlat},{maxlon} near the parcel.
Request daily precipitation with GET /cdo-web/api/v2/data?datasetid=GHCND&datatypeid=PRCP&stationid={id}&startdate=...&enddate=..., passing your token in the request header.
Aggregate returned PRCP values (tenths of mm) to compute design storm or seasonal saturation figures for the drainfield sizing worksheet.
For a longer daily-normals baseline instead of raw daily data, use the NORMAL_DLY dataset on the same endpoint.
Known gotchas
NOAA has been migrating CDO functionality toward the newer Access Data Service (ncei.noaa.gov/access/services/data/v1) -- if the v2 token endpoint or dataset stops responding, fall back to that endpoint, which uses different parameter names.
The free token is rate-limited to 5 requests/second and 10,000/day, which is easy to exceed if you loop station-by-station for a large service territory.
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