When winds are light, a three-cup anemometer records the velocity, as it is especially sensitive. Wind speed is measured by the rate at which the cups turn. However, stronger winds, over 30 miles per hour, tend to put a lot of wear and tear onto such an instrument, and cause its bearings to wear out prematurely. Using a customized application for a piece of aviation hardware, the Observatory's pitot vanes into the wind and measures its speed essentially through the pressure exerted through a hole in the front of the instrument. The reading is then recorded on a wind chart in the Observatory's weather room, and is also converted to an electronic signal for other purposes.
Air extends to the top of the atmosphere and exerts pressure on all the air below.
On the summit there is less air above to exert pressure upon it than there is in the valley, thus causing the lower barometric pressure on the summit. After the storm had passed, the anemometer was taken down to be tested for accuracy. It proved to be correctly calibrated and thus the top wind speed become officially accepted.