In actuality, the free Weather app on my iPhone calls for a 20% chance of rain today based on a 30% prediction of rain at 10:00pm.
The Weather Channel app also calls for a 20% chance of rain based on a prediction of anywhere between 15% and 35% chance of rain.
Then there's the roguish AccuWeather app, which calls for a 60% chance of rain based on an hourly forecast from now to midnight of between 20% and 56% chance of thunderstorms.
I wasn't a math major in college (that's Our Daughter), but I'm fairly certain if your hourly report says the greatest chance of rain is 35%, then you shouldn't be low-balling at 20%. Likewise, if you're calling for a 56% chance of rain at any point in the day, then the greatest chance of rain you should be predicting is 56%, not 60%. Imagine my boss's reaction if I told her I fully expect to make 100% of my annual goal based on an expectation of never exceeding 67% of any of my monthly goals. It sounds like the kind of mathematical acumen you'd expect from an English major.
These apps don't seem to play loose and free with numbers when it comes to the temperature.
Today's high temperature is consistently predicted by all three apps to be 86 degrees Fahrenheit and the low tonight will be 71 degrees. When I check the hourly forecasts, I clearly see where the high and low temperatures fall throughout the day. None of the apps say the high today is 86 degrees but at 3:00pm it'll be 92 degrees, or the low tonight will be 71 degrees but at 10:30pm we'll have snow. That would be ridiculous! The high is the high and the low is the low, and no other numbers are dangled out there in the minutiae to the contrary.
Maybe there's some greater-concept thinking going on at national weather central headquarters that I simply don't comprehend. Maybe an over-riding formula beyond the grasp of my simplicity is applied that factors the forecasted potential for precipitation and averages it out to a number that, while seemingly ungrounded in reality, is soundly based in scientific actuality.
For instance: If the greatest chance of rain is 35% at 8:00pm, and the least chance of rain is 5% at 4:00pm, and there will be seven hours of cloudless sky before noon with at least three hours of severe thunderstorms (with hail) after sunset, and if the color of the liver of a sacrificed park pigeon is favorably red, and there's enough milk in the fridge for all the Oreos in the pantry, and it's been more than six months since any of the college interns have filed a sexual harrassment complaint with Human Resources, then the chance of precipitation today is 20%. That's the only way it makes sense to me.
I understand weather forecasting is just a best guess given available scientific data. Fronts move, winds change, storms stall, hurricanes shift direction and unexpectedly gain strength off the coast... Anything can happen and frequently does. I don't expect the different weather apps to agree with each other, but at the very least they should agree with themselves.
So, will it rain today? Who knows...
© 2016 Mark Feggeler