Excerpt from Valley 101: A Slightly Skewed Guide to Living in Arizona, a collection of Clay Thompson’s columns for The Arizona Republic. (Originally published April 2, 2000.)

What a question! Could you possibly be any dumber? Did you think of this question while you were getting dressed in the dark?

Partly cloudy or partly sunny?

What were you thinking? Is that it?

Sorry, just venting a bit there.

Actually, this is a very good question and one that I never really thought about much, but which now intrigues me greatly, especially because it came in twice in a week.

My first guess would have been that there’s not much difference at all, kind of like the difference between the two major political parties or the difference between Madonna’s cover of “American Pie” and a that crud under the refrigerator.

You know, there should be some sort of law about stuff like that.

But I digress.

It turns out there actually is a difference between partly cloudy and partly sunny, according to Austin Jamison, a meteorologist at the Phoenix office of the National Weather Service and a very patient person who is willing to speak slowly and in words of few syllables for those of us who don’t catch on very quickly.

First of all, says he: It is a somewhat subjective matter. But in a nutshell, if there is going to be less than half opaque cloud cover, the forecast will be partly sunny. If there is going to be more than half opaque cloud cover, it will be partly cloudy.

There also is a day/night issue here. The degree of daytime cloud cover tends to affect, obviously, the partly sunny question because a partly sunny forecast for the night hours would be fairly remarkable and perhaps the subject of an entire column.

Opaque is one of those words that has always given me trouble (see question No. 2 above). I always have to look it up. In the case of cloudiness, it means you can’t really see the blue sky very well or the
stars or very much moonlight.