Jungfrau, Matterhorn and Mont-Blanc

What is the temperature and windchill up these mountains in late July?

Would a gore-tex jacket + fleece enough for taking cable car (not hiking) up these mountains?

If you're just going up by train or cable car for a couple of hours exploring (not skiing all day ) you should be fine with a sweater and whatever summer jacket you have along (jean jacket or similar) - just make sure youre not wearing shorts and sandals.

It wouldn't be a bad idea to take a light weight jacket but you probably won't need it.

It also could very easily be shorts weather,it was for us incl. our 7&9 year olds at the Matterhorn

Good thinking, Atoto: One July we were caught in a snowstorm on Jungfrau, one that extended on our ride back down to the junction at Kleine Scheidegg. I think your light gore-tex/fleece idea would have been fine. Might I also suggest a cheap pair of gloves (one of those 99cent kind in Walmart) and really cheap stocking cap to stuff in your pockets. Have always found that these type of hat/gloves take up no room but are the easiest way to get warm fast!