Use only https://aviationweather.gov/api/data/metar?ids=EGLL&format=json for the newest valid METAR observation at EGLL, London Heathrow. Return uint256 = obsTime * 2 + wet, where obsTime is that row's Unix observation time, and wet is 1 if a current-weather group in wxString contains RA or DZ (rain or drizzle, including -RA, SHRA and FZRA); ignore groups beginning RE or VC. Otherwise wet=0. Absent, null or empty wxString means no reported rain only when rawOb is a valid EGLL METAR and not NIL. If the API fails, the report is missing/invalid, or obsTime is future or more than 90 minutes old at retrieval, report unavailable rather than a number. Never infer from clouds, humidity or forecasts.