How come when weathermen call for all day thunderstorms, you never hear thunder?

When a forecast is made, it is made for a huge geographical area. Just because it isn't happening in your backyard, doesn't mean it isn't happening. Along the same lines, just because an event IS happening in your backyard, doesn't mean another area in the forecast region is getting it.

When I worked as a forecaster, a thunderstorm was only called that if the thunder could be heard. Lightning did not count. I know that might sound stupid initially, but especially after dark lightning can be seen when many miles away. This only counts as a thunderstorm to those who are close to it.

I think that you may be distinguishing between embedded thunderstorms (which tend to occur on large scale weather systems such as cold fronts) and the thunderstorms that develop purely due to daytime heating and convection.

For the first category, because the weather front is moving across a wide area during the forecast period, the risk of thunder anywhere is higher, but there may only be one rumble of thunder heard (apologies if that is not the US term, as I am in the UK).

In the second, because many places will miss the storms and some may have bright sunshine for most of the day, the chances of any individual area getting one are statistically lower, but when you do, it will be a proper thunderstorm with lots of lightning and thunder, and probably a slow moving storm as well.

I hope that makes sense.

.....weather is completely unpredictable,, even with today's technology, they cannot 100% predict the weather,, but at least a higher percentage of it will likely happen,,