20 December 2007

Weather forecasting

One way I procrastinate and/or pass time is by reading the archives of long-running blogs. Today it's glenn mcdonald's furialog, because I was thinking of buying the My So-Called Life box set, but decided against it because it's $70; mcdonald used to write a music review column called The War Against Silence which I liked, the first installment of which was written five days after the last episode of that tragically short-lived television show aired. mcdonald was a fan of the show, and I was bored this morning, so I thought of his blog. (For the record, he's a programmer by trade but not by training, although this may be irrelevant.)

Anyway, he wrote on 13 January 2005, commenting on weather forecasting:
But what I would hold someone responsible for, if I thought it weren't a pervasive cultural flaw, is the destructive precision with which uncertain predictions are communicated. Weather is merely the most obvious daily public manifestation of a fundamental reluctance, or perhaps an inability, to say what we really know, rather than what we wish we knew.

Similarly, I've watched a bunch of Walter Lewin's introductory physics lectures in the last few days (I've mentioned this before) and he has drummed into my head that a measurement without uncertainty is useless. What is true for measurements is doubly true for predictions.

It would be interesting to see error bars on weather predictions, but we never will. One can get something like this, though, for the tracks of tropical storms at Weather Underground; they show the outputs of various computer models. If these models all show a storm going in the same direction, one can be fairly sure it will actually go in that direction; if the projected paths are spread out, one knows not to be so sure. I wonder if it is possible to determine the accuracy of more mundane weather predictions by, say, tuning into a large number of different TV channels, web sites, and so on which make independent forecasts. If it were possible to get archived weather forecasts I'd take a look; as it is I don't think I can find out what people on July 14, 2006 (say) thought the weather would be like on July 18, 2006, so the only way I could collect data would be to wait, or perhaps to call up some weather-forecasting entity and ask, and I don't care quite that much.

The fundamental reason we don't see error bars on weather forecasts, though, is because they are brought to us for the most part by profit-seeking entities, and such entities really don't want to advertise "we don't know what's going to happen!" -- even though everybody knows this. This is the "pervasive cultural flaw" that mcdonald refers to above.

Also, although I cannot produce data for this, I seem to perceive that at least certain weather forecasting outlets use only even numbers of (Fahrenheit) degrees in their forecasts, not odd numbers. If this is true, I suspect it means that they believe they can't be accurate to within one degree.

No comments: