We conduct exclusively spectroscopic projects which are possible on partly cloudy and cirrusy nights. Our observers are eager to observe and frequently try to utilise every possible clear patch on the sky. The cloud cover shows a seasonal effect in that the winter nights are definitely more cloudy. They are also much longer than summer nights so that, if a night is clear, then much more observing can be done. Very useful information on the monthly and hourly variation in cloudiness in years 1990 - 1999 have been provided to us by Mr. Robert Morris, Meteorological Service of Canada, Environment Canada.
Seasonal effects are moderate.
These clouds are pockets of high moisture swept by the NW winds from these two lakes. Our Telescope Operators use several weather Web resources to monitor the weather, including the satellite images and radar images, so that relatively little time is lost due to weather uncertainties. Some data on the frequency of photometric weather is available in the form of a short article by Don Fernie in Jour. He estimated that there are 580 hours of photometric weather per year. This looks like a quite good number to the undersigned because my impression is that we have frequent cirrus clouds associated with the jet stream.