You know its been cloudy for too long when:
- you see constellations in the cloud patterns.
- you see nebulae in the cloiud patterns (and, of course, being an astroholic you'll refer to them by their NGC numbers).
- you estimate the level of cloudiness by the magnitude of the brightest star that can't shine through them.
- you sometimes just sit in the observatory and... and have a little cry
...
Al.