Hi Ric,
NLC = Noctilucent Clouds - a phoenomena only visible in summertime at latitudes 55-65 degrees from the equator. Essentially very high (90-100km) ice clouds illuminated by the Sun over the pole.
You can listen to me talking about them on BBC Radio Ulster last year here...
http://www.pevans.me.uk/images/peonru060605.mp3
Not well understood but seem to bear an inverse relationship to sunspots.
Clear skies,
Paul.