Friday, September 5, 2008

Weather modeling at the NHC

This is another "not really about the web but I did find it there" posts.

In my post on the National Hurricane Center I said it was fascinating to get to know the personalities of the various computer models. Well, fascinating for a geek, at least. If, like me, you like that sort of thing, the NHC's explanation of what models they use, and how, and why, is a veritable feast. Some of the high points:
  • There are a dozen basic models, plus several more ensemble models combining them.
  • The forecasters don't rely on any one model in making a forecast. There's no "model of the day". Instead, they consider the results of all of them and make a judgment call.
  • The aggregate results of the models are generally more accurate than any particular model. Another "wisdom of crowds" effect, if you will.
  • The NHC continually reviews its forecasts to see whether the models and the official forecasts are "skillful" A forecast is skillful if it's more accurate than the statistical models, which just look at what past hurricanes have done and don't even try to take current weather conditions like wind and sea surface temperature into account.
  • By that measure there are skillful models, but it's a difficult bar to clear. Not quite "dumb is smarter", but dumb is smarter than you might think.
  • In particular, it's only now becoming possible to predict the intensity of a storm skillfully. Predicting a storm's track skillfully is less of a problem.
  • Finally, implicit in the whole report is the understanding that in good science and engineering, it's vital to know what you don't know.
Weather forecasting is a notoriously hard problem. It was one of the drivers behind the discovery of chaos theory. The NHC's technical model summary provides an excellent window into the process of using computer modeling on hard problems in the real world. It also gives some insight about how and whether to use "dumb" statistical models and how and when to try to be "smart". Good stuff!

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