Recent years, noctilucent clouds seems to appear quite often in the northern hemisphere during the months of June and July. One to two hour(s) after, or before sunset, watch carefully the northern to eastern horizon for bluish cloudiness. The distinction between Cirrus (altitude usually 10 km) and the noctilucent clouds (altitude around 80 km) may pose some problem for the not so experienced sky watcher. But when the sun is between 1 to 2 hours below the horizon, the Cirrus appears always as a dark feature while the noctilucent clouds appear quite bright.

This picture was taken with both clouds present, the dark Cirrus with an orange glow of the street lights and a thick pack of bluish noctilucent cloudiness.         

More pictures of special clouds via this link