The winning move in yesterday's U23 race came on the final lap first of three short sharp climbs in the final 4k of each lap. It started raining lightly during the final lap and the cobbles were wet. The winning Frenchman got a small gap, and held it (barely) to the line. (Absolutely great move, by the way) A Belgian favorite attacked from the middle of the road on the cobbles and immediately lost his back wheel and went down. There is a narrow cement apron on the sides beginning about half way up that may be key.
It's been raining lightly all night, so the cobbles may be cleaned off and less slippery. It will rain on and off for the men and women's elite races. Overall, perhaps rain will reduce their effect as a potential place to attack rather than increasing it?
The climb in question (Libby Hill), before the crowds arrived:



U19 women on Libby Hill:




This is Hill #2, (23rd street), most of the way up. It's straight, and smoother and grippier than Libby Hill: