It's not unusual to get strong winds behind a cold front, but Monday's 81 knot (93mph) gust at the Roanoke Regional Airport had meteorologists scratching their heads. 


After some checking it appears a bird caused the erroneous report.

Phil Hysell, Meteorologist at the National Weather Service office in Blacksburg confirmed "It is believed a bird landed (as opposed to hit) the Roanoke ASOS ultrasonic wind sensor this morning, resulting in the erroneous  81 knot wind gust."

The sensor is much different from the anemometer and weather vane that is typically used on your average weather stations.

A three-pronged, stainless steel device has no moving parts and is virtually maintenance free. There's even a heater to keep snow/ice from building up during the winter months. 

So how did the bird cause the wind?

On these instruments, wind speed and gusts are obtained by the time it takes for sonic pulses to travel between the transducers (the three prongs that are transmitting and receiving pulses). Using the combined measurement from these transducers a wind speed and direction can be obtained.

Hysell explains, "When a bird lands on this sensor, the tail will block the path between the transducers, or generate wind by the shaking of the bird's tail feathers which results in an erroneous reading in both direction and speed." 

In this case, the 81 knot wind.

Click here for more info on the Vaisala ultrasonic wind senor used at the National Weather Service observing site.