We had a very interesting “Weather Brains” podcast this week. This is our weekly thirty minute audio show all about weather; distributed free via iTunes and the Internet. The host is my old weather associate from the Channel 13 days in the early 1980s, David Black, and most weeks you hear from people like J.B. Elliott, Brian Peters, Bill Murray, Jason Simpson, John Oldshue, and myself.
This week’s episode somehow drifted onto the subject of using “probability of precipitation” in weather forecasts. These “POPs” are used by the National Weather Service, and some broadcast meteorologists. Long time readers know my dislike for POPs. People remember them, but very few understand them, and they usually lead to confusion. In fact, within the next two weeks I will write my annual post here about summer weather forecasting in Alabama, which includes a little about how the “chance of rain” parameter is pretty much useless on a summer afternoon here in the Deep South.
I learned during the podcast that even weather people really don’t understand “POP”. I think everyone on the show had a different idea about the definition of “POP”, but we were all in good agreement that they are horrible in a public forecast. I poked around and found this definition for “POP”:
"If a forecast for a given county says that there is a 40% chance of rain this afternoon, then there is a 40% chance of rain at any point in the county from noon to 6 p.m. local time. This point probability of precipitation is determined by the forecaster by multiplying two factors: Forecaster certainty that precipitation will form or move into the area X Areal coverage of precipitation that is expected."
Listen to the podcast here:
http://www.weatherbrains.com/
And, read the entire explanation of "POP" here:
http://www.utexas.edu/depts/grg/kimmel/nwsforecasts.html
This week’s episode somehow drifted onto the subject of using “probability of precipitation” in weather forecasts. These “POPs” are used by the National Weather Service, and some broadcast meteorologists. Long time readers know my dislike for POPs. People remember them, but very few understand them, and they usually lead to confusion. In fact, within the next two weeks I will write my annual post here about summer weather forecasting in Alabama, which includes a little about how the “chance of rain” parameter is pretty much useless on a summer afternoon here in the Deep South.
I learned during the podcast that even weather people really don’t understand “POP”. I think everyone on the show had a different idea about the definition of “POP”, but we were all in good agreement that they are horrible in a public forecast. I poked around and found this definition for “POP”:
"If a forecast for a given county says that there is a 40% chance of rain this afternoon, then there is a 40% chance of rain at any point in the county from noon to 6 p.m. local time. This point probability of precipitation is determined by the forecaster by multiplying two factors: Forecaster certainty that precipitation will form or move into the area X Areal coverage of precipitation that is expected."
Listen to the podcast here:
http://www.weatherbrains.com/
And, read the entire explanation of "POP" here:
http://www.utexas.edu/depts/grg/kimmel/nwsforecasts.html
on May 17, 2006, 8:38 pm
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