Well, weekends are always horrific. By the time of your arrival, everyone will be out for summer, so the parks will get busy. If you get there at opening, the park will be empty for 2-3 hours and the rides will be a walk on.
For most of June the weather is overcast, cloudy, and chilly (chilly for a Californian :lol. That's called June Gloom. The extremely hot weather doesn't usually start till July.
Since it'll be summer, DL will stay open till midnight.