As monsoon nears, time for a refresher on dew point
From June 15, 2004:
What is the dew point, and why should we care?
This is like the mockingbirds-singing-at-night question.
Every year I explain this to you people, and every year it comes up again. I attribute this to newcomers, and being a genial, accommodating sort of person with a boyish mien, I shall patiently answer it again.
It is not just the dew point. It is the dew point temperature. The dew point temperature is the temperature of the air when it is cooled to saturation.
Remember that warm air can hold more water than cold air. When the air temperature is 95 degrees, 1 cubic yard of air can hold 1.85 cubic inches of water. At 50 degrees, the same cubic yard can hold only 0.44 cubic inches of water.
Now if the dew point temperature is, for example, 55 degrees, that means that at 55, the air is saturated with water and cannot hold more. So dew forms.
What it comes down to is that when the dew point is high, it’s pretty muggy out. But then you probably already knew it was muggy even without knowing the dew point.
What is the difference between isolated showers and scattered showers?
OK, the National Weather Service uses words like “slight chance,” “chance” or “likely” to describe the degree of the threat (or promise) of rain.
If they say there is a “chance” of rain, that means there is a 30 to 50 percent possibility that measurable rain will fall somewhere in the forecast area.
“Isolated,” “scattered” and “numerous” come into play when it seems almost 100 percent likely that rain will fall somewhere in the forecast area.
Those words describe the percentage of the forecast area expected to get rain.
“Isolated” or “few” means 10 to 20 percent of the area probably will get rain. “Scattered” means 30 to 50 percent, and “numerous” means 60 to 70 percent.
And mockingbirds sing at night to attract mates.