Weather APPS are OK, but you need to know where the data is being recorded vs the actual track location. There can be notable differences at some tracks! However, it's better than nothing.

HERE'S Justin Lamb on FB answering a question about weather stations.

I'm helping someone remotely right now who is racing in Phoenix. I have two predictions running; one from an online weather source and he's sending occasional screen shots from a friend's weather station.

The numbers are definitely different between the two sources, which doesn't really matter as long as they "move together" proportionately. I've only used weather station data before, and this experience isn't changing my mind at all on that.

With that said, there was a bad run yesterday that had us scrambling a bit to know what might be wrong. It would have been real easy to see with a data recorder.

Data logger.

Air Density Online is ok, but the issue I have with it is that what it generally shows isn't quite what I see at the track, and the updates are slow during the day....The advantage to the weather station/prediction software is that you can tie your run into the weather reading AT THAT PARTICULAR time. Racing in Denver and now in Alaska, I've seen the weather swing so much between rounds that you can be off as much as a tenth and a half or more from one run to the next because of that...