As the one who answers pesky practical questions, please tell us what the “chance of precipitation” means. Thursday evening’s forecast was for 40 percent snow. Does that mean it will snow 40 percent of the time that evening? Or is there a 40 percent likelihood that it will snow at all someplace? – Renee and Todd
Here’s your Action Line forecast: Today, you’ll be alit with a little alliteration, with 100 percent chance of intermittent puns. Expect a snow job, with scattered thinking under a cloud of suspicion.
As they say, “You don’t need a weatherman to know which way the wind blows.”
They also say, “The trouble with weather forecasting is that it’s right too often for us to ignore it and wrong too often for us to rely on it.”
“They” are Bob Dylan and Patrick Young, respectively.
We don’t want retribution for a lack of attribution, precipitating a storm of protest.
Regardless of which pundit said what, weather forecasters are given a bad rap.
And by bad rap, we mean unfair criticism and not the latest insufferable ditty from Kanye West.
The atmosphere is a vast, complicated and three-dimensional force that is constantly changing and evolving. Forecasters have to make sense of it and then predict the future.
The National Weather Service, for example, collects trillions of data points from all over the place and from all kinds of sources.
That information is plugged into several models, or astoundingly complex computer simulations, that provide probable outcomes.
Naturally, not all of the models agree with each other.
That’s where the “chance of precipitation” comes in, according to Michael Charnick, a National Weather Service forecaster stationed in Grand Junction, where the numbers are crunched for Durango-area weather.
“The ‘percentage’ comes from the results of the simulations. It’s statistical, along with some expert interpretation,” that determines the likelihood of rain and/or snow, its duration and severity, he said.
Thus, a 60 percent chance of snow mean that about 60 percent of the models point to snow occurring.
Moreover, he said, the forecast is for a specific area for a specific time.
“That’s why percentages often change within the same general area during the same timeframe,” he said.
Michael pointed to the difference in percentage chances of snow in Durango versus Purgatory. Some short 25 miles and a couple thousand feet of elevation make a huge difference.
Oftentimes, forecasters make the wrong call. Thus, to air is human, atmospherically speaking.
We expect too much from weather reports. For some reason, the meteorologists are held to an unreasonable standard of statistical perfection.
Consider that the greatest hitter in baseball, Ty Cobb, had a lifetime batting average of .366, or a 36.6 percent chance of connecting with the pitch.
But it also means Cobb had 60-plus percent chance of striking out or hitting a fly ball.
What we need to do is put the “me” in meteorology.
If you get caught in some unpredicted weather, blame yourself and not the person who said there’d be a slight chance of showers.
Keep this in mind: There’s no such thing as bad weather, just bad clothing.
And remember, the most accurate meteorological prognostication in history came from a comedian.
It’s classic George Carlin: “Weather tonight: dark. Turning partly light by morning.”
Email questions to actionline@durangoherald.com or mail them to Action Line, The Durango Herald, 1275 Main Ave., Durango, CO 81301. You can ask for anonymity if your 24-hour weather channel is a window.
