What does it mean in weather forecasting when the weatherperson says “40% chance of rain”? What factors are being considered to come to this prediction?

Question

A lot of times on the news, the meteorologist says, “today there is a 40 percent chance of rain” or “80 percent chances of snow”. What factors go into making this decision?

In: 2

Answer 1

From Weather.gov:

>To summarize, the probability of precipitation is simply a statistical probability of 0.01″ inch of more of precipitation at a given area in the given forecast area in the time period specified. Using a 40% probability of rain as an example, it does not mean:

>(1) that 40% of the area will be
covered by precipitation at given time in the given forecast area or

>(2) that you will be seeing
precipitation 40% of the time in the given forecast area for the given forecast time period…

>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.

[Source](https://www.weather.gov/media/pah/WeatherEducation/pop.pdf)