by Jay Freeman
I took my NexStar 8 to Montebello on Wednesday 14 November and encountered near-classic subsidence conditions. About half a dozen observers were there when I arrived, at about 7 PM, and they reported that it had been clear till five minutes ago, but low cloud was slowly drifting from the East and obscuring the sky. It appeared to be fog or cloud cap forming over the slightly higher ridges just east of the Montebello site. Wind was near calm, only by wetting my finger and holding it up could I detect the eastward movement that was apparent in cloud motion.
Surface conditions were not too wet, but as people started packing up, the fog descended till we were in thin stuff. I commented that if a few more people would leave, it would probably clear. They did, and it did. With thin fog nearly obscuring the horizontal view in many directions, the sky was clear, and I began observing. After a while my corrector plate dewed over -- I had not thought to bring my large battery so could not use my Kendrick stuff. No problem, though, I just put the OTA and drive base assembly in the car and ran the engine and heater for a while.
By that time, the last person but me had gone, and the fog had descended slightly below the level of the site. The weather felt more dry, and the tendency to dew was much reduced. I observed for a while, but by about 10 PM high cloud moving in from the west was beginning to be a problem, so I packed up.
Notwithstanding adverse meteorology, I completed both my Messier survey and my Herschel-400 survey with the NexStar 8, so I was quite happy with the evening.