If there is a 30% chance of storms is it FOR SURE it will rain?

Answer 1

It is sort of interesting how forecasters apply probabilities. Although all forecasters go through statistical courses and from those, they all develop different ideas and methods of how to apply probabilities to the forecast. It has evolved into sort of a game between the model driven, statistical derived formulas and the guess of the forecaster.

In years gone by, forecasters learned that the forecasted probability in the forecast was the product of two probabilities. The first was the area coverage of measurable precipitation (0.01 inch or for the purist 0.005) multiplied, by the confidence of the forecaster. So if a forecaster was 50 percent sure of a 50 percent coverage of measurable rain, the forecast was then for 25 percent. Well that worked in theory, but most forecasters figured that they were 100 percent sure of THEIR forecast so probabilities became mainly an areal term.

Today, due to the increased pressure put on forecasters to get it right and improve on the verification of the model (man against the machine theory), it has turned into a game. They get to see the percent that model determines is the most correct and because they don't want to lose, will either accept that number unless they find a reason that the model is totally wrong and that betting against that number will increase their verification score against the model.

Model guidance is very good compared to 40 years ago. In fact some companies make money by doing nothing more than taking the model numbers and selling them as the forecast.

But even those numbers are only based on the percentage of the number of times that it rained when the atmosphere was in a similar condition.

The answer is, No, it isn't a sure thing.

Answer 2

Probably not. I think it means that there is a 30% chance that it will rain somewhere in the area at that time, but not necessarily where you are. And 30% is not a high percent anyway.

Answer 3

No, unless you are planning a picnic. 8-)

What they mean when they say 30% chance of rain, is that in similar circumstances, it rained 30% of the time.

So take an umbrella.

Answer 4

Where I work we are in a little dip...so any thing below 50% and we get rain over that and it will go around us literally.. We have watched it comming then just split go around and rejoin behind us. So to answer your question it depends on where you live.

Answer 5

No...that just means there is a 70% chance it WON'T rain.

Answer 6

No, because there is a 70% chance that it wont,
So, 70 beats 30 doesnt it??

Answer 7

No___ the probabilty is 3/10

Answer 8

There is no FOR SURE in meterology. Everything is based on probability.