Start of NLC season

June and July are typically the start of NLC or Noctilucent Clouds. Those highest clouds we know are showing up around 80km above Earth's surface. They are very cold and exist of very small ice crystals. When sunlight hit those crystals they will show up as a blue glow. They appear during the summer months and the best way to observe is about 2à3h after sunset or 2à3h before sunrise.

The picture below I took last last year mid July, 1h before sunrise.