Satellite West

How accurate are the precipitation precentages in weather predictions?

It's calling for a 40% chance of rain or storms in Ohio and I'm going out with my grandma. It would be really nice if these predictions were not accurate lol. SO how accurate are precipitation precentages usually?

Public Comments

1. Well the accuracy is directly related to the amount of time they are forecasting into the future. Obviously if they are talking immediately they are going to be 100% right. But since these predictions are mode using computer models and multiple variables the uncertainty get higher the further out you forecast. So if they are saying today the percentage is fairly accurate. If they are forecasting a week from now not so much.
2. I think it can vary from one area to another and the quality of your local weather forecaster. Here in New York the percentages are usually very accurate, meaning if they predict at least 70% chance of rain it will rain. 40% is not high enough for me to take an umbrella. Know that I base this on comparing the weather with the forecast for a number of years going now. Just happen to like numbers... When I read the weather description, it's usually more off than the percentages!