This work presents a thermal sensor that can simultaneously measure wind velocity and ambient temperature. It consists of a silicon chip that is heated slightly above ambient temperature and is exposed to, and thus, cooled by the wind. Wind speed and direction are determined via two thermal sigma-delta (TΣΔ) modulators, which control and digitize the 2-D heat distribution in the chip. Ambient temperature is determined by measuring the modulator's period of oscillation, which depends on the thermal diffusivity of silicon, and is a well-defined function of ambient temperature. For wind speeds ranging from 1m/s to 25m/s, the sensor's error is less than ±4% (speed), ±2° (direction) and ±1°C (temperature) for temperatures ranging from -40°C to 50°C.