BCTV Weather Station - Channel 193
The BCTV weather information system is broadcast on TV channel 193 and displays the current weather conditions at the BCTV station operating 24 hours a day. We use the Davis Vantage Vue weather station connected to a computer which generates the pictures for the broadcast. The audio is provided by the National Weather Service from Albany N.Y., with current conditions, forecasts and emergency warnings for the Pioneer Valley.
Besides the common quantities like temperature, wind speed, rain total etc., other measurements are displayed. Here is brief explanation of some of the other measurements we display.
The dew point is the temperature below which the water vapor in air (at constant barometric pressure) condenses into liquid water. The condensed water is called dew when it forms on a solid surface. The dew point is a water-to-air saturation temperature. The dew point is associated with relative humidity. A high relative humidity indicates that the dew point is closer to the current air temperature. Relative humidity of 100% indicates the dew point is equal to the current temperature and that the air is maximally saturated with water. When the moisture content remains constant and temperature increases, relative humidity decreases.
The heat index is an index that combines air temperature and relative humidity in an attempt to determine the human-perceived equivalent temperature or how hot it feels. The result is also known as the "felt air temperature" or "apparent temperature". For example, when the temperature is 90 °F with very high humidity, the heat index can be about 105 °F.
Absolute and Relative Humidity
Absolute humidity (expressed as grams of water vapor per cubic meter volume of air) is a measure of the actual amount of water vapor (moisture) in the air, regardless of the air's temperature. The higher the amount of water vapor, the higher the absolute humidity.
Relative humidity (expressed as a percent) also measures water vapor, but RELATIVE to the temperature of the air. In other words, it is a measure of the actual amount of water vapor in the air compared to the total amount of vapor that can exist in the air at its current temperature.
Barometric pressure is the force exerted on a surface of the Earth by the weight of air above.
Measurements of barometric pressure and the pressure tendency (the change of pressure over time) have been used in forecasting since the late 19th century. The larger the change in pressure, the larger the change in weather can be expected. If the pressure drop is rapid, a low pressure system is approaching, and there is a greater chance of rain. Rapid pressure rises are associated with improving weather conditions, such as clearing skies.
The more rapid and extreme the pressure change over a few hours, the more extreme the weather change you can expect. This is particularly true with wind changes. If the pressure is changing and if the tendency is downward, expect more stormy weather on the way. If an upward and quick change, storminess is moving out and clearing may be coming in the very near future.