... wanted to check the weather for my arrival. So I selected the Acars Atis and checked the information, I then for some reason compaired it to my ASN window. The two were very different and I was wondering if you had to be with in a certain distance of the airfield to get the correct info.
I've been struggling with this issue for years. It came up with all kinds of addons I've been using. I've been discussing it with several addon developers throughout the recent years.
To make a long story short, here is the conclusion:
The weather we see in the sim (P3D and FSX are the same in this regard) is not really produced by the weather engine (like ASN or Opus). It is produced by the sim itself using the data, the weather engine injects. And the sim is said to be not very good in doing this; and it becomes worse the further away from your aircraft it is. When the weather engine injects the weather the sim deals quite well with it around your current position. Further away the weather produced by the sim goes more and more astray from what the weather engine injected.
So the weather in the sim at stations far away from your position can be totally differrent to what your weather engine says. And since PF3 reads the weather in the sim (through FSUIPC) and not the weather of the weather engine, the destination
ATIS is unusable as long as you get closer to your destination.
I found the limit to be somewhat between 50 and 80 nm. So if you want to be sure to get a reliable
ATIS wait until you are 50 nm from your destination.
By the way this is also the reason why you might sometimes see AI aircraft landing and departing in opposite directions. The AI aircraft flying the „wrong“ direction was told to do so when you where still far away from the destination and the weather was not yet accurate. This was a major problem some years ago, when I often landed and found myself facing an AI aircraft taking off. By now the weather engines found ways to minimize this problem and it works quite well (still problematic with calm or variable winds).
Hope this helps.
Regards
Ralf