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Wind and Wind Chill Questions Answered

Can you explain wind chill?

The wind chill is an index set up for human comfort, based on heat transfer theories between the air and body as well as skin exposure.

We all have a very thin layer of air just above our skin that helps insulate our body against the cold. When we expose our skin to windy conditions during the winter, that layer of air is displaced. That exposes the skin to the harsh winter air. If the temperature was to only reach 22 degrees with a wind of 15 mph, that would produce a wind chill of 9 degrees.

If you want to calculate the wind chill as we go through the winter months log onto www.noaa.gov.


Have you ever heard of wind prospecting?

Just as prospectors ran to California for gold in the early 1800s, power producers seek the windiest places on Earth to place windmills for power generation. To produce adequate power to pay for a windmill, each power generation site must have an average wind speed greater than 10-12 miles per hour.

Remember that the relationship between wind speed and the force that wind produces on a given surface is not a linear function in mathematics. As a result, a site with average wind speeds of 15mph will produce over three times the amount of energy as a site with 10mph average winds over the course of a year. Variations in tree cover and elevation greatly impact wind prospecting.

A local windmill for power generation can be found east of Webster on Rt. 104.


Can you explain what the term “shear” means?

When 13WHAM meteorologists use the term shear, we are referring to a change in the wind; either vertically or horizontally. But to be more specific, there are two types of shear; directional and speed.

Directional shear is when the wind direction, when traveling up or down through the atmosphere, changes significantly. In contrast, speed shear is when the wind speed changes with height.

For example, at the surface the wind might be blowing at 10mph, but at 5000 feet, the speed might be 70mph. This difference represents speed shear. When forecasting weather, shear can have an impact on such diverse elements as thunderstorms or lake effect snow


How does an anemometer measure wind speed?

Meteorologists use a few different types of anemometers.

One type of anemometer is a hot-wire anemometer. The hot-wire anemometer measures the wind speed based on variations in temperature or electric resistance of a metal wire. As the wind speed increases more energy is used to keep the metal wire at a preset temperature. Wind speed is determined by measuring the electrical consumption of the wire. This device is not typically used for official National Weather Service wind measurement.

Another type of anemometer and probably more familiar type is a rotation anemometer. This device measures wind speed based on the rotation of a sensing element such as a propeller or spinning cups. As wind speed increases the anemometer will rotate faster. Portable versions of this anemometer are also available.


How is wind direction measured?

Wind direction is one of the most recorded measurements in meteorology today.  However, it still carries a bit of confusion. Meteorologically speaking, the wind direction is the direction that the wind is coming from, not the direction it is blowing to. The wind is measured in terms of degrees (going clockwise) with zero representing north.

There is also the question of whether we measure wind from true north or magnetic north. The answer is true north, and this is an important distinction to make. The difference between true and magnetic north can be as much as 25 degrees in some places, which is enough to produce significant errors.


What causes the wind to happen?

Before the wind even starts blowing, we must look toward the sun for this answer.

Incoming solar radiation heats the surrounding land and water which then produces heat for the Earths surface and atmosphere. But not all surfaces or locations heat at the same rate. This difference in heating creates a difference in air pressure. The resulting "pressure gradient force" causes air to move from areas of high pressure toward areas of low pressure. This movement of air can be considered the wind.

Most often we observe what is called a large-scale wind circulation, which is driven by low or high-pressure centers. This wind pattern may affect an area in the range hundreds or thousands of miles. However, wind can also be felt on a local scale such the Lake Ontario lake breeze.


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