What is the significance of dew point?
The dew point is the temperature at which moisture condenses from the air to form dew. The dew point is related to relative humidity: when the air is humid the dew point occurs at a higher temperature than when the air is dry. Once dew begins to form, the air temperature begins to drop more slowly. When temperatures reach freezing, the dew turns to frost. If the air is very dry, then the dew point will be very low, and it is often lower than 0ºC. If this occurs, frost injury can occur without the appearance of frost. Growers should not wait for frost to form before they turn on the irrigation system. Growers can use dew points to estimate how low and how quickly the temperature might drop in any given night. Dew points can be obtained from: • Environment Canada (This site provides current dew points and other current weather conditions, for certain locations.) • Farmzone.com. This site provides forecasted dewpoints. How much water to apply: The amount of water applied per hour is based
Growers can use dew points to estimate how quickly the temperature might drop in any given night. Once dew begins to form, the air temperature drops more slowly because heat is released. Frequently, the nighttime temperature drops to the dew point, but not much below it. Sometimes the dew point is referred to as the basement temperature. If the air is dry, then the dew point will be low. If the dew point is below 0°C (32°F), frost forms instead of dew. Black frosts occur when temperatures are below freezing but above the dew point. Don’t wait for frost to form before starting the irrigation system (especially when the humidity is low).
