Between  Tuesday the 24th of May until approx Tuesday the 8th of August

Noctilucent Cloud (NLC) could start to appear in the NW sky 90-120 minutes after sunset

or 90-120 minutes before sunrise in the NE sky

these dates may vary a little dependent on current solar activity

 NLC have a typical colour range of electric blue to silver

and are normally at an altitude of 250,000-280,000 feet