>Hi Mark,
>
>First of all, my congratulations to you as MOTD :)
>
>Second, I thought today at morning about probability and finally I understood the difference. Let's me explain:

As my college professors explained it, it's the possible number of outcomes over the total number of possibilities. That is why there is always a 50% chance of precipitation; it will either (rain/snow/sleet/hail) or not. So, you have one possibile outcome over two possible occurrences.