There isn't just one "instrument for weather". Weather forecasting relies on a whole array of instruments, each measuring different aspects of the atmosphere. Here are some examples:

Surface-based Instruments:

* Thermometer: Measures air temperature

* Barometer: Measures air pressure

* Anemometer: Measures wind speed

* Wind vane: Shows wind direction

* Hygrometer: Measures humidity

* Rain gauge: Measures rainfall

* Snow gauge: Measures snowfall

* Weather vane: Indicates wind direction

Upper Air Instruments:

* Weather balloons (Radiosondes): These carry instruments that measure temperature, humidity, wind speed and direction, and air pressure at various altitudes.

* Satellites: Provide images and data about clouds, temperature, moisture, and other atmospheric conditions over large areas.

* Radar: Detects precipitation and other atmospheric phenomena like storms.

Other Instruments:

* Doppler radar: Provides more detailed information about precipitation and wind speeds.

* Lightning detectors: Track and measure lightning strikes.

* Buoys: Measure ocean conditions like wave height and water temperature.

So, there's not a single instrument for weather, but a whole system of instruments that work together to gather information and provide a comprehensive picture of weather conditions.