Το ASOS (Automated Surface Observing System) είναι το primary surface-weather-observing network των ΗΠΑ. Designed για nonstop updates κάθε λεπτό, ανεξάρτητα, σε >900 αεροδρόμια. Ανά την NWS Forecast Office, το ASOS αναφορά sky conditions (cloud height/amount) έως 12.000 ft, surface visibility, basic current weather (type/intensity βροχής/χιόνι/παγετός), pressure/altimeter settings sea level, air/dew-point temperatures, wind direction/speed. Δεν αναφορά tornadoes, funnel clouds, ice crystals, blowing obstructions (snow/sand), δεν βλέπει beyond horizon.
Radar (RAdio Detection And Ranging) χρησιμοποιείται από 1940s για precipitation detection. Enhancements για precise storm examination. Doppler radar = modern version, detects intra-cloud motions high resolution. Premier source severe weather, NWS relies heavily για weather-warning operations. Λειτουργία: emits short bursts near-light-speed radio waves από rotating antenna. Radio waves reflected ("echo") received between bursts. Distance/intensity εγγραφής/analyzed.
Το NWS λέγει radiosondes employed 60+ years για weather data ολόκληρο το atmosphere depth. Μικρό, expendable device κρεμασμένο από μπαλόνι, μετρά pressure, temperature, relative humidity. Data sent to ground receiver via battery-powered transmitter. Wind speed indirectly measured tracking radiosonde position in flight. Μπαλόνι 5ft tall x 4ft wide at liftoff, expands to 2-story building height at 100.000 ft. Ascends >115.000 ft before burst, small parachute slows descent. Drifts to ground, citizens can mail back to NWS.
