## The Probability of Precipitation: What Does it Mean? Part 2, A New Resource

A while back I posted on this topic, starting with my father-in-law’s quirky (but charming) interpretation of probabilities quoted in weather reports, and continuing to discuss the meaning of probability in the context of weather forecasts. I suggested that someone ought to check on the accuracy of such reports, and listed a few resources. There are plenty of papers published in technical literature analyzing forecasting models, but it would be nice to have some sort of analysis that is accessible to those of us who are not experts in the field.

Here is an interview with Eric Floehr at John D. Cook‘s very interesting blog. Floehr does exactly what I had wanted (assesses the accuracy of published weather forecasts), although for a cost. How curious am I?

I have taught mathematics and physics since the mid 1980s. I have also been a textbook writer/editor since then. Currently I am working independently on a number of writing and education projects while teaching physics at my local university. I love math and physics, and love teaching and writing about them. My blog also discusses education, science, environment, etc. https://qedinsight.wordpress.com Further resources, and online tutoring, can be found at my other site http://www.qedinfinity.com
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### 2 Responses to The Probability of Precipitation: What Does it Mean? Part 2, A New Resource

1. Joe says:

PoP is pretty confusing. The 9th edition of The Atmosphere text by Lutgens and Tarbuck describes it so:

‘For example, a forecaster can have a high degree of confidence that a storm will move into an area (say, 80 percent), but determine that only 40 percent of the area will be affected. Under these conditions, the forecaster will call for a 30 percent chance of precipitation (0.8 X 0.4 = 0.32, or about 30 percent). Although precipitation is nearly certain, the chance that it will affect you, wherever you are in the forecast area, is only 3 in 10.’

Here’s a study that the Bulletin of the American Meteorological Society conducted several years ago:

http://journals.ametsoc.org/doi/pdf/10.1175/1520-0477%281980%29061%3C0695%3AMOPPF%3E2.0.CO%3B2

• Santo says:

Hi Joe,
The excerpt from the book highlights the complications in interpreting PoP statements, and it reinforces the idea that my father-in-law was on to something!

So, besides trying to find out how often the forecasts are correct, it would be a real public service if someone would take the time to elaborate on the excerpt you quote and say in plain language just what a PoP really means.

Thanks!