Or a bit more exotic Cortina D'Ampezzo would generally be low 20's. Some great single pitch sport climbing in the forests which gets less attention than it deserves due to the longer routes and via ferratas towering above.
This is an eternal issue for me, as the big teacher holidays fall at a time when most well known european sport destinations are too hot. The classic venues are Ceuse and Rodellar, but the crowds keep me away.
It depends what grade you are after, but you could do a lot worse than getting the Schweiz Extrem guidebooks, and heading to Switzerland. Lots of great crags that are high up and cool (Simplon Dorf is a great example). And you get the added bonus of lots of multipitch routes if you want them, and obviously great walking and mountain biking (or long granite slabs) for rest days.
Another good option is the Austrian Tyrol. Zillertal, Schleirwasserfall, Chinesisiche Mauer. There's an excellent Tyrol sport climbing guidebook available. Again, lots of good mountain biking too.
A place I never managed to get to due to buggering up my ankle at the start of the trip, was the Picos de Europa and Costa de Verde area in Northwest Spain. There's a new guidebook just out to the area which looks like a superb summer venue.
High Alps, Ecrins national park area. Cracking sport climbs all around the area.
If you stay near the Lake Serre-Poncon you can go east all the way up to Briancan area in under an hour or west to Orpierre in about the same time. The lake is massive and fed by the Durance so the water stays lovely and cool all year
Just back from there, I used "undiscovered alps" to arrange a few days single and multi pitch sport climbing with my children, really good.
I also go with the Ecrins. The climate is hot during those months but there is always plenty of shaded climbs and the humidity is low because its up in the mountains. Some great camp sites that get popular with the climbing crowds.
The only problem is, its a bit of a drive unless you fly to Turin and hire a car.
Most visiting climbers will camp up at Ailefroide because its high up and so the evenings are much more bearable and of course there is rock to climb all around you. You don't have to go to the campsite either, which is here: http://www.ailefroide.fr/camping/ but can go higher up, past the village/shops and just set up a pitch. They may charge you but its very little because its so basic. The beauty of being up so high is, you won't get pestered by flies.
We noticed all of France and the Alps was quiet. Normally after Bastille day, the Alps etc get busier not this year. The big lake -Serre Poncon - was quiet, normally the lakeside campsites are bursting. We mtb rode in Alp DHuez and only 20 or so bikers.