Through conversations that I have had and from some of the questions I have received I have realized that not everybody fully understands what percentage for rain means. I can’t really make a Weather 101 out of this topic, so I thought I would just explain it in a simple blog.
When we say there is a chance for rain, for example a 30% chance for rain, that means there is a 30% chance that somewhere in our area we will receive a measurable amount of rain. Measurable meaning at least .01 inches, a trace of rain (recorded as 0.00) does not verify.
I think one common misconception is that the percentage means the amount of our area that will see rain, so using my example of 30%, people might think that means 30% of our area will see rain, and that is not true.
We will try to narrow down the area affected if at all possible. For example, in the summer time with an active sea breeze, most of Central Texas might stay dry, but our southeastern counties could have a chance of seeing some rain, so we might put “20% southeast”. This would mean that there is a 20% chance for rain in our southeastern counties.
One last point… The percentages do not have anything to do with the amount of rain. It seems a lot of people think that the higher percentage of rain the more rain we will get, but they do not correlate. We could have an 80% chance of rain, but if it rains it will be light, and on the other hand, a 20% chance of rain, but if it rains it could be heavy downpours. That is why we will usually also either show the forecasted rain amount, or we will say what kind of rain we are expecting, i.e. isolated light to moderate rain, or scattered heavy rain, etc.