Last weekend, someone asked me how I manage to come up with the topics for my daily columns. That’s a great question and to be very honest, when I started my job here more than two years ago, that was a concern of mine. Now I see that between Grandma’s wisdom, Mother Nature's temperament, your weather questions and great photos, it’s not a problem.
Today's topic is dew. When I received this fabulous photo from Linda Wozniak, I was reminded of something Grandma used to say. I’ll get to that in just a moment.
Let's start by defining the dew point: the dew point is the temperature at which air becomes saturated. In other words, the dew point is the point to which air must be cooled for the air mass to become saturated – assuming there is no drastic change in air pressure. On a clear, windless night, with no change of air mass, the air temperature drops to reach its dew point. It can never drop below the dew point.
It is a true measure of how much water vapour is in the air; the higher the dew point, the more water there is in the air, and the lower the dew point, the drier the air mass is. In the summer, the dew point is an excellent tool to use in determining how comfortable, or uncomfortable, it feels outside.
Back to Grandma and this: “dew on the grass, rain will never come to pass.”
Dew forms when the temperature falls to the dew point overnight - any further cooling will produce dew. These conditions are more likely to occur under the centre of a high-pressure system where it's usually cloud-free and windless. If the sky remains clear all night, you can usually expect another eight to 12 hours of fair weather before the outgoing side of the high gives way to clouds on the leading edge of the next system, an area of low and some rain.
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Cindy Day is the chief meteorologist for SaltWire Network
