Humidity.  I don't care if it 0 degrees or 90, as long as there is no humidity-I am okay.

I will say that any day you are scheduled to race with bad conditions is the worst.  Otherwise you can usually work through it and actually enjoy it.

2nd to that would be HAIL. I was running home one time and it started pouring rain. Then suddenly there was hail the size of golf balls. Holy cow - can you imagine how much I picked up the pace?! Fortunately a neighbor saw me out there and picked me up. Made for a nice impromptu speed workout though.

I also recall once early this year I had a 20 miler planned and I had to run through more than 9 inches of snow. The city got inundated and did a horrible job plowing the roads. So we were jumping through drifts, etc. Wouldn't you know that all of the bike paths were clear as a bell?!! Needless to say I had stabilizing muscles I didn't even know I had that were extremely sore after that!

Hehe. Another time I doing a long run and with the wind chill it was about -6. A friend passed me and said "nice ice." I had no idea what he was talking about until he completely passed me and I saw he had a nice little shelf of ice on his back from where the sweat froze. Nice. I completely forgot about it and got home where I stupidly did not change immediately. Once the shelf on my back started to melt I was FREEZING! It took me about 3 hours to get my temps back to normal!!

But I agree that it is all character building, chest thumping stuff. This is the good stuff.

On a different note. My favorite runs are during a nice fluffy snow when everyone is out on a Sunday morning shovelling - not too cold so everyone is social and a good mood. Next to that has to be anywhere from 60-80 degrees and raining.

Or when you have a race with perfect weather.   !http://www.coolrunning.com/forums/biggrin.gif|src=http://www.coolrunning.com/forums/biggrin.gif|border=0!