Going to Geneve for the month of June. Planning on some light excursions nearby (within 70km) and maybe some light hiking, possibly along the Aravis Range.
Should I bother bringing shorts? Do I need a heavy coat? Should I have boots for snow at 2500m or so, or will it be gone by June?
You have two options, go with the averages over several or even many years or look at a weather forecast about 10 days before you leave and keep looking once a day or once every few days to see the predictions develop.
I would personally go with the second and use your own home situation to base your plans on.
It always pays to bring shorts and rain gear, as rare hotter and wetter days are always possible.
And keep a very good eye on the snow line. If the weather turns bad that line can come down the mountains rather fast.
I was in Geneva last June and the weather was pretty varied. The pattern tended to be cooler in the mornings, baking hot by midday and a nice mild temperature on an evening with warm showers appearing from nowhere anywhere in between!
My go to for these sort of trips is usually shorts, jeans, a jumper/hooded jacket and a light weatherproof jacket. Layers are key!
