Why
Zed completely breaks Norra's rhythm: he does not play poke, he plays for the kill. Your zoning loses a lot of value once he has access to his ultimate. Even if you win early, he can reset the lane with one well-timed all-in.
Lane impact
You lose lane control from level 5 onward. You can no longer hold an aggressive position, and every wave becomes risky. You are forced to react instead of pressuring.
How to play
Force him to use W defensively with gradual poke. Keep your defensive tool only for his ultimate, never for trading. Critical timing: level 5 plus lethality recall, then the first enemy jungle roam that can set up a dive. Avoid trying to poke to win lane after level 5, using your defensive spell before his engage, or staying mid without side vision. Good signs: Zed uses W to farm, you force his ultimate without dying, and the wave stays close to your tower.