You Won’t See a 50% Chance of Rain

 

Eric Bickel is a high school friend and is now leads the Graduate Program in Operations Research at the University of Texas.  The joke is we were probably the most unlikely pair from high school to get into science-related jobs.  One of the projects he did was compare the National Weather Service, The Weather Channel and a private forecasting company forecasts to each other.  The findings are interesting and can be found here:

http://journals.ametsoc.org/doi/abs/10.1175/2011MWR3525.1

The key to a good forecast is having sharpness and resolution.  Resolution, for example, is if you say there is a 40% chance of rain it will rain 40% of the time, or four out of every ten days you put 40%.  Sharpness is if you say it’s going to rain it will rain, or if you say it won’t rain, it doesn’t.  Sharpness is giving some certainty to the forecast.  In a normal year, without a drought, if I put a 30% chance of rain every day, by the end of the year my forecast will have good resolution because it will have rained on average once every three days.  However, I’ll have poor sharpness because I’m never really saying if it is going to rain or not.

One of the things that stuck out to me from Eric’s work was the Weather Channel avoids putting a 20% and 50% chance of precipitation.  The 50% omission is intentional.  The Weather Channel believes that users will interpret a 50% chance of rain as a lack of knowledge (after all there are only two possible outcomes), when, in fact, a forecast of 50% is more than twice the climatological average and thus a strong statement regarding the chance of precipitation.  Bickel shows in his paper how this policy degrades the quality of their forecasts.

To view past weather quiz answers click here:

Past Weather Quiz Answers

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