Edward Willett

Weather forecasting

I know this is a sensitive topic, but sometimes it’s necessary to face life’s unpleasantries. It’s time I wrote about weather forecasting.

I know, I know, this time of year it seems like anybody could forecast the weather. “Miserably cold this weekend, but springtime’s just around the corner — not!” But believe it or not, a lot of scientific effort goes into weather forecasting. The fault lies not in our weathermen, but in our atmosphere, that we are shivering.

The study of weather is called “meteorology,” which puzzled me as a youngster. Shouldn’t “meteorology” be the study of meteors?

Well, it is, if you’re an ancient Greek. “Meteorology” derives from “meteoron,” which referred to any phenomenon in the sky. Most of us only call “falling stars” meteors, but meteorologists speak of hydrometeors (rain, snow, clouds), lithometeors (solid particles — sand, dust or smoke), photometeors (optical phenomena like rainbows or mirages) and electrometeors (lightning).

Meteorology, then, involves a lot more than just weather forecasting: it’s the study of how the Earth’s atmosphere works–how it produces hurricanes like Andrew, or the thunderstorms that periodically hammer us just for the hail of it.

The knowledge gained by that study is what has made today’s weather forecasts so accurate. Quit snickering! Until relatively recently, the best you could do was look at the sky, stick a finger in the wind and maybe, if you’d lived in the area for decades, make a better-than-average guess. You have to admit we do better than that (well, usually).

Modern forecasting arose from several scientific advances, beginning with the invention, between 1650 and 1750, of the three principle instruments of weather observation: the thermometer, which measures temperature, the hygrometer, which measures humidity, and the barometer, which measures air pressure. Then came the telegraph, which made it possible to quickly gather observations from many locations at the same time. This began to reveal how weather systems move and develop.

The big breakthrough was the development of the polar front theory in the 1920s by a Norwegian scientist Wilhelm Bjerknes. His theory accounted for the large-scale movement of air masses and how they influence wind and precipitation. In the 1930s, improved radio technology made it possible to send radiosondes, balloon-borne instrument packages, into the upper atmosphere, which helped refine polar front theory by, among other things, revealing the presence of the jet stream, the high-altitude, high-velocity current of air that determines the movement of many weather systems.

In the next few years, American meteorologist Jule Charney succeeded in reducing the horrendously complex equations governing the atmosphere’s behaviour to a usable form, which coincided with the development of electronic computers to chew on them..

Today, powerful computers in many countries digest reams of data from hundreds of observation sites (including satellites, which have themselves revolutionized forecasting) to provide so-called numerical forecasts–but that’s not to say that weather prediction is just a matter of looking at a computer printout. Far from it!

A weather forecast can be divided into three steps: observation and analysis (“What’s it doing outside?”), extrapolation (“What’s it likely to do next?”) and prediction of particular variables (“The high today will be … “)

The computer excels at extrapolation: it can give a pretty good indication of whether it’s going to get hotter or colder. But to actually predict the temperature, or the likelihood of precipitation, forecasters draw not only on the computer model, but on their own observations and knowledge. Experience counts.

Thus, the forecaster bravely goes out on a limb and makes what is still, despite all our technological efforts, only an educated guess. The more long-range the forecast, the more of a guess it is, because the atmosphere is so incredibly complex its future behavior can be altered by tiny variations too small to measure — or, as it’s often illustrated, the flap of a butterfly’s wings this spring in Regina could lead directly to a hurricane in the Bahamas weeks later.

In other words, no one, almanac-writer or Environment Canada forecaster, will ever be able to tell you in June precisely what the weather will be like on your birthday in July.

So don’t blame the forecaster when he predicts sun and rain pours down instead. Pity him: faced with our contrary atmosphere, he’s doing the best he can.

Poor chap.

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