This strengthens the argument by addressing a potential weakness. It provides additional information that reinforces the meteorologist's assumption that the proportions he compares are comparable, as his station is more accurate even with a larger number of predictions.

This does not affect the argument. How many meteorologists a station employs and their status of employment (i.e., whether they’re full-time, part-time, etc.) does not provide us with information about how reliable or useful their station is in predicting the weather.

This does not affect the argument. A station being able to put on a good investigative news report doesn’t tell us anything about its weather prediction abilities.

This does not affect the argument. We don’t know if this policy affects the station’s accuracy, and we have no reason to believe that all its competitors don’t share this policy.

This does not affect the argument. It could be that on all the days the station predicted it would not rain its competitors predicted the same—but still, the station has a higher accuracy of predicting rain on the days it rained. This doesn’t change anything for the argument.