It was -30 F. I was at 2000 feet over the forest. I knew that the front part of the top window was trying to go up as the glass was following the shape of the top wing! On the ground the glass was flat so it went more forward. The front part of the glass was not bolt on! So what had to happen happened and... whoosh I lost the top glass. The plane started a shallow dive right away. The tail was in turbulence and the stick was saking. I throttled back, reduced the speed and was afraid that the tail was hit. I looked throught the top hole and saw that the tail was ok. Ouf! I landed straight ahead on a lake. I was on skis. So, yes you can fly without the top glass but with a lot of turbulence on the tail. A good check to do is to look at the front part of the glass if it is well anchored. Fly safe.