For your 'true horizon' to be 60 miles then you will need to be stood at 2400 feet above sea level (about 3/4 of the way up Snowdon ), looking across the sea.
The 'visible horizon' will be much less as it's used to describe the horizon when objects like trees, buildings, hills etc obscure to 'true horizon'.

The 'visibilty' may well have been 60 miles or more from your location, but trying to judge the distance based on the edge of a cloud layer that could be thousands of feet above sea level is going to be very difficult because you're looking at the edge of the cloud at an angle, not horizontally. So the edge of the cloud will be much further away from you than the visible or true horizon.

If that all makes sence?

__________________

I read an article not so long ago regarding this subject. The conclusion was,due to the curvature of the earth,at ground level the horizon is approximately 20 miles.
If I can find the article I will post it here.

__________________

Hey Grant
When I was at sea, the formula used to be :-
1.12 sq.rt HE (ft)
presumably you were RN?
looking over the horizon ;-)
I was MN (48yrs)

__________________

Thanks Budgie, certainly is very interesting. Hmm how high is the QE2 road bridge? 65 m (213 ft) above the Thames apparently. Not sure if that is 3/4 of Snowdon or not
The cloud was very high and a thin, flat sheet

__________________

I took the calculation from Wikipedia's description of the Horizon. According to this formula, if you're stood at sea level then the distance to the 'true horizon' is only 3 miles (rounded up).

As an example, on a clear day I can see the Isle of Skye from a beach near to us. The northern tip of Skye is 35 miles away but if I look through binoculars at Skye then I can't see the base of the cliffs because they are below the horizon. What I can see if the top third of the cliffs that protrude above the horizon.
So this tells me that the visibility is more than 35 miles but it doesn't mean that the horizon is 35 miles away.

__________________

Your distance to the 'true horizon' from the QE2 Bridge will only be 18 miles at that height, using the forumula I posted above.

__________________

hmm how odd - thanks for working it out though

__________________