IPMA vs US Weather

IPMA's open-data service is a plain directory of continuously-refreshed static JSON files, not just a single forecast endpoint: it covers daily/hourly weather forecasts, real-time station observations, sea-area and district warnings for mainland Portugal, the Azores and Madeira, plus separate seismic and biology (pollen) datasets from the same institute. No registration is required, though IPMA asks heavy users to email its webmaster for usage statistics.

The National Weather Service API serves official US government forecasts, active alerts, and observation-station data as GeoJSON and JSON-LD feeds, with no signup or API key required. It's widely used by third-party weather apps and accepts direct browser calls, though it requires a descriptive User-Agent header identifying your application on every request.