Not dissimilar to a mid-December day in Glasgow, the rain was torrential. As we'd previously holidayed in Germany, Georgia, Prague, Vienna and Kathmandu, we'd learned the lessons of layering, waterproofs and good boots.
We booked 2 days in advance as our time was limited and we didn't want to waste time queuing for tickets or a place in the queue.
On the day, it was hissing down with rain with intermittent sleet.
The experience, I am sure, on a sunny day would be magnificent and should we return to NYC, will do this again. The interactive system showed panoramic views of what it is like when visibility is good (instead of 3 feet).
One experience we did have an is a WARNING. - we walked down the side of the tower and a large lump of ice smashed beside my wife. This happened several times and could be a real killer. Ice forms at the top, breaks off and falls in lumps or shards. We could see this at the top, SO BE CAREFUL !
WTC Memorial was also excellent.