An anemometer is a device used for measuring wind speed, and is a common weather station instrument. This well made anemometer is designed to sit outside and measure wind speed with ease.
To use Anemometer Wind Speed Sensor w/Analog Voltage Output, connect the black wire to power and signal ground, the brown wire to 7-24VDC and measure the analog voltage on the blue wire. The voltage will range from 0.4V (0 m/s wind) up to 2.0V (for 32.4m/s wind speed). The sensor is rugged, and easy to mount. The cable can easily disconnect with a few twists and has a weatherproof connector.
Adafruit Web Site: https://www.adafruit.com/products/1733