SEATTLE - In Sept. 3's column, we talked about how Seattle is near the bottom in the U.S. with only an average of 58 sunny days a year. But it's not like a weather observer looks up at noon, sees the sun, and calls it a sunny day.
There are sensors that can actually measure when the sun is indeed shining on it. These sensors will track the number of seconds the sun was shining on it, and divide it by the number of seconds of daylight for that given day.
If the sun shone on the sensor for 70% or more of the day, it's considered a sunny day. If it was between 20-70% of the time, it was a partly cloudy day, and 20% or less, it's a cloudy day.