One could argue that a taxpayer subsidized weather service kills private competition. How do you compete with free?
Of course, all those arguments miss the point. The weather service is an important function of the government, we shouldn't have to pay for weather. It's a matter of public safety and information, the property of the commons, not some commodity. Protecting that is the reason we have a government, not to artificially support a Senator's local business.
I completely agree with your reasoning on why weather data is public data. Its actually not an argument about business at all but one of the public interest.
To expand on you reasoning a bit I think there is a general test we can apply to all government data collection and publishing practices. If the data is being collected then its been determined to be in the public's interest to do so and therefore it's also in the public interest to release it freely in a reasonably accessible format. If the set is not useful then releasing it serves to at least inform citizens that we're wasting money so we can exert pressure to stop collecting the useless set.
The exception of course is gov data that may have privacy or security implications but nevertheless eventually it should be released when those concerns are no longer valid.
Of course, all those arguments miss the point. The weather service is an important function of the government, we shouldn't have to pay for weather. It's a matter of public safety and information, the property of the commons, not some commodity. Protecting that is the reason we have a government, not to artificially support a Senator's local business.