Growing up in the midwest, precipitation was a metaphysical certainty. The wind blows from west to east (if it blows in any other direction, you're in serious trouble). There are no geographic features to slow or disturb a front as it moves through. From the right vantage point, you can watch a storm come in for, literally, hours before it hits. But it will always hit.
In the south, count on no precipitation until it is falling. Has it gone twilight dark at 2:00pm? Do you see endless thunderheads in the sky? Is it raining nearby, as part of a storm that is very clearly headed in your direction? None of these mean anything: in the last week, I have seen all these fail to result in rain. (There has also been a random thunderstorm, not visible on radar, that camped out over our house for 30 minutes.) Why all this happens I could not possibly say.