Actually, minor correction here to two above posts. With clear sky, laser pointers can be seen that far, if aimed accurately. With any for or amount of crap in the air, not a change.
Here I live in this dorm through the workdays, and I have a buddy of mine living aproximately 300 meters of airline distance from me.
We have been pointing 1W blues (well, 800-900mW likely, but you get the idea) to eachother. There is a building in the way, but aiming right above it gives you the feeling you're pointing the beam few meters above my friend's window. Same goes from him - he says he's pointing the beam really really low. However, to me it looks like the beam is passing around 20-30 meters above me. I am not sure of actual distance to the beam at 90° Angle.
He also says I'm pointing the laser too high, but I'm going as low as the building in the middle permits.
Visibility of the incoming laser was, surprisingly, very low. Possibly due to high divergence, but it looked like equal brightness 50mW greenie he was pointing towards me.
Then one night there was this fog as dense as milk outside. I was like "Woo point the blue one over here". Much to my dismay, I saw apsolutely nothing through the fog.
I had my Arctic at the time and across the street there was a building aproximately 25 meters away.
The beam of light barely reached the building, I could only barely make out the dot. All the light gets lost in the fog along the way.
So no, if there's any fog at 2 miles, it will be really difficult for anybody to see the beam since they cannot see buildings they normally would see without fog.
Without anything, and with recent rainfall so there's clear air, you could perhaps aim the beam towards a friend 2 miles away. It would be best he had a high visibility laser too, so you can "locate" eachother.
We're talking 300mW+ greens or at least 1W blues here. Best to have high power green because of smaller divergence of the beam.
