https://www.techradar.com/news/steam-summer-sale-2018-looks-set-to-start-today

It's time. The sun may be shining, but you're about to spend the next few weeks sat in front of your gaming PC, as the Steam Summer Sale 2018 is set to kick off today.

That's information courtesy of the Steam Database Twitter account, which has reliably pointed to the kick off date of previous seasonal steam sales.