Add NOAA NWS weather fallback

Docs/TechnicalDesignDocument.md

@@ -165,6 +165,15 @@ contract and can perform a live Open-Meteo request for every source-backed tile
 in `Data/Tiles/tile_weather_manifest.json`. This keeps the provider global for
 all future real tiles instead of adding one-off Ground Zero weather code.
 
+NOAA/NWS is the US-only fallback and enrichment path. The provider contract is
+stored in `Data/Weather/noaa_nws_us_fallback.json`. The weather provider
+subsystem can check whether an active tile center coordinate is inside the
+approximate NWS coverage window, request `api.weather.gov/points/{lat},{lon}`,
+follow `properties.forecastGridData`, and parse gridded temperature,
+precipitation probability, and wind speed as fallback inputs. The NWS path is
+only used for eligible US/NWS-covered tiles; Open-Meteo remains the global
+source for all tiles.
+
 ## Terrain And Tile Delivery
 
 ### MVP Tile