Know your data sources.

NOAA NCEI historical climate data via the keyless Access Data Service: - Daily summaries (GHCN-Daily): TMAX/TMIN/PRCP by station + date range - Climate normals (1991-2020): annual, seasonal, monthly heating/cooling degree-days (HDD/CDD) - Station + dataset discovery (by bbox or id) CRITICAL USAGE RULES: 1. No auth — keyless /access/services path, NOT the token-gated CDO v2 API 2. Degree-days (HDD/CDD) drive heating-oil / natural-gas / power demand — getDegreeDays() weather-normalizes production/load and models seasonal gas demand 3. Daily temps scaled tenths-°C→°C, precip tenths-mm→mm; degree-days are whole, °F base (65°F) 4. searchStations() (bbox order north,west,south,east) finds station ids for the data methods

NOAA CO-OPS — water levels, tide predictions, currents, coastal met. No auth. - searchStations ⭐ NWLON 301 + tidepredictions 3.4K / currentpredictions 4.4K / historicwl 2.9K / watertemp / met / harcon - getStation (expand: datums | sensors | harcon | products) - getWaterLevels ⭐ observed (preliminary + verified). 31-day cap. - getTidePredictions ⭐ hi/lo (365d) or 6-min (31d) / hourly (365d). - getMeteorological ⭐ wind / air_temperature / water_temperature / air_pressure - getServiceInfo upstream quirks: HTTP 200 + body {error:{message}} on bad input — check body. 3 response shapes (water_level, predictions, currents_predictions). Datums product removed — discover via mdapi expand. Long-period stations only support hourly_height/high_low; Great Lakes accepts IGLD.