# Why can't the meteorologists predict for sure if the day would be rainy even on the beginning of the day sometimes?

Why do the meteorologists still cannot predict if a day would be rainy or cloudy or blizzardy even on the beginning of the day sometimes?

My life circles around weather and an avid weather watcher.

And I noticed the computers still are not advanced enough to get all the variables to predict the weather accurately. The weathermen and women still read the probabilities. For example, there is a 70% chance of rain. I take the umbrella outside and there is no rain. Then the prediction is the day would be cloudy. But then there is rain. I am not saying it happens most of the time. But it happens sometimes.

Do we need a quantum computer then with qubits? Because it can hold a myriad of variables and consider them in the calculation of the weather.

• Chaotic Evil butterflies
– user967
Commented Sep 5, 2018 at 3:59

$\mathrm{POP} = C \times A$
where $C$ is the confidence it will rain somewhere within the forecast region and $A$ how much of the area will experience the precipitation.