Fetch daily or hourly reference evapotranspiration (ETo) and weather data from CIMIS for a station, zip code, or coordinate

Steps

1. Register a free account at cimis.water.ca.gov and generate an appKey; authentication is solely by appKey, no username/password is sent per request.
2. Call GET https://et.water.ca.gov/api/data?appKey=<key>&targets=<list>&startDate=YYYY-MM-DD&endDate=YYYY-MM-DD, where targets is either all station numbers, all zip codes, all lat/lon pairs, or all street addresses — target types cannot be mixed in one request.
3. Set dataItems to a comma list of needed fields (e.g. day-asce-eto,day-precip,hly-asce-eto); if omitted, CIMIS returns its default bundle of about 13 daily fields.
4. Set unitOfMeasure=E (English, default) or M (metric), and for zip-code requests set prioritizeSCS=Y/N to control whether the 2km-gridded Spatial CIMIS System or a physical Weather Station Network station answers the query when both could.
5. Set the Accept header to application/json or application/xml to choose response format, and check each item's Qc (quality-control) flag before trusting a value, since missing/flagged readings are still returned.