Trivia 082: It never rains but pours

Wintertime in western Washington is usually pretty dreary. Lots of rain, near constant cloud cover, and really early sunsets. However, once summer arrives, this gets flipped on its head. Lots of clear skies, and nights where the sun doesn’t set until after 9pm. Right now, though, we’re approaching the liminal state of spring. You can’t quite ever tell what the weather is going to be like, so you have to be prepared for most anything. Case in point, it’s been pretty wintry the last week, but we’ve had a few days of clear weather. Enough that I could go out to do some photography. I am keeping an eye on the forecast this week, because we are supposed to have some nice clear days coming up.

If you have ever watched a meteorologist on the nightly news, you know that their forecasts don’t necessarily match up with what actually happens. Now, although it may feel like this is fairly common, keep in mind that you are more likely to notice the one time the forecast is wrong, rather than the hundred times it is correct. But this isn’t helped by the fact that meteorologists use some specialized terms when referring to weather phenomena. Some of these terms have rather specific meanings, which are not always apparent. For example, rain versus drizzle. To me, “raining” means water is coming from the sky, and “drizzling” refers to a kind of constant, slow rain. But here are the definitions according to the American Meteorological Society:

  • Rain: Precipitation in the form of liquid water drops that have diameters greater than 0.5 mm, or, if widely scattered, the drops may be smaller.
  • Drizzle: A type (or form) of precipitation consisting of water droplets less than 0.5 mm (0.02 in.) in diameter and larger than 100 μm.

As you can see, the distinction has nothing to do with the intensity of the precipitation or its duration, simply the size of the drops.

Another good set of terms to know are the terms used for intensity and uncertainty. For example, when a meteorologist says “chance of snow”, many people think that means it’s more or less a coin toss as to whether or not there will be any snow. And that’s not far off. “chance” refers to a 30-50% probability that an area will have snow. But these values are actually defined beyond just a hand wave. In addition, there are qualifiers for the area of effect a weather pattern will have. If a meteorologist says “scattered showers”, this means that about 30-50% of an area will experience showers. If they’re talking about a city, that could be a lot of land. So even though you might not have any showers on a particular day does not mean that other parts of your area did not receive any.

Speaking of showers, that’s another term which has its own definition. A “shower” is defined as precipitation which can abruptly start and stop, and is usually strong, but short-lived. This means that it typically will not affect large areas, but will be rather localized, both in space and time. So again, when the weatherman says “scattered showers”, and you don’t experience a drop, that just means you happened to miss all the affected areas.

Ultimately, weather forecasting is a lot more precise than we give it credit for. Personally, I am looking forward to the good weather we have coming up to go out and shoot some more timelapses. So keep an eye out for new videos (link below)!

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