I will have a 72 hour layover on Iceland 1–4 May, and I will happen to have my bicycle with me. I am considering to go on a cycling trip to þingvellir and some other places. However, I'm unsure about weather conditions. Should I expect þingvellir to be covered in snow at the beginning of May? I don't mind if the hills/mountains are snowcovered, but I'll be cycling with my summer tyres so if snowfall or snow-blocked roads are likely, it might be wiser for me to make different plans.
I would say no, not on the roads or paths, but there is only one thing you can expect from Iceland's weather - that it's unpredictable. Last year I've been to þingvellir in late February and there was no snow on roads or paths, unless you drove through the mountains. However, this year the winter they have is so fierce, they consider giving it a name!
I recommend these websites when planning trips:
Have fun! Iceland is a truly beautiful place.