When are comming the summer promotions on Steam?

summer

AFAIK, Valve did not yet announce anything, you have to be patient.

Last summer sale was June 30th - July 10th

Near end of June

You missed it.

Well, given the weather here... It'll be a while before summer. >.<

AFAIK, it'll be as DopeFich said, end of june - middle of july ish.

When the sun rises in the west and sets in the east, when the seas go dry and mountains blow in the wind like leaves. Then the sales will return, and not before.