Originally Posted by bobs
Clouds should have no effect on GPS reception. Remember, GPS was originally designed as an all-weather navigation system for the military and is a pretty robust system.
My old Garmin GPRSII handheld (no maps, just OS grid ref, plotted course etc) was definitely affected by cloud cover and could fail to acquire without a clear view of the sky. That was the old 8 satellite technology though. I don't think the modern 12 sat systems are affected too much by clouds. I was playing with a TomTom Bluetooth GPS receiver recently and it even acquired my location in my office!