Statistical Accuracy of Internet Weather Forecasts

markmcb writes "Brandon Hansen considers the statistical accuracy of popular on-line weather forecast sources and shows who's on target, and on who you probably shouldn't rely. Motivated by a trip to a water park that was spoiled with hail despite a 'clear sky' forecast, he does a nice job of depicting deviations, averages, and overall accuracy in a manner that stats junkies are sure to love."

Comments

Can we believe the forecasts?

[gavink42]

Personally, I take weather forecasts with a couple of grains of salt.

However, the last cold blast that came through Memphis was forcast almost a week ahead of time. Weather radar of the middle part of the country showed about 90% clear of storms. So, I had a hard time with that one.

To my surprise (and right on time), down came the blast of cold air. Soon after was the promised snow/ice.

It still seems like an inexact science... with a touch of art and a pinch of luck thrown in for good measure.

Re:Can we believe the forecasts?

[Daniel Dvorkin]

What I find funny is that the entire practice of weather prediction is based on a logically fallacy. They take the data from previous years and say, ok, last time conditions looked like this x happened, so we predict x will happen again. Anybody who's taken an introductory logic class knows that you can't correlation does not equal causation.

And anyone whose understanding of correlation goes beyond "an introductory logic class" knows that in fact, as long as you're very careful about what you're doing, you can in fact very often use observed correlations to make valid predictions.

There's this whole field of study called "statistics," see. Not the "X% of people surveyed believe Y" type of thing you hear on the news, but an actual science, grounded in rigorous mathematical theory and growing more sophisticated all the time at producing useful knowledge from mountains of data. People get PhD's in it and stuff. Really. Maybe you ought to read about it some time. Maybe even take a class.

Or perhaps you'd rather remain secure in your prejudices, repeating "correlation does not equal causation" like a mantra, snickering at people whose knowledge you choose not to understand.

Re:Statistics don't lie Statisticians do!

[Overzeetop]

Actually, you're only considering the accuracy of the scientific forecast. That is essentially useless to the end user - what they (I) want is accuracy of the reported forecast. The difference? I don't care when the actual prediction was made, I want to know that when I look at the forecast, it is likely to be correct. A very accurate forecast that is only updated once every three days is not nearly as useful as a farily accurate forcast updated every ten minutes. The former would be the best by your yardstick, but wouldn't necessarily help determine if the likilihood of a hail storm was high for this afternoon as much as the latter.