The sky is the real ticket. The tower only holds you up to it.

Haze

Haze wastes the trip. That is the line I want in your head. Summer humidity plus city air turns the skyline into a pale smear. You still get the drop in your stomach. You do not get the map. If the buildings across the lake are already soft from the street, a timed entry buys you a higher smear. I would walk the harbour instead and keep the tickets for a harder horizon.

Lake-effect cloud

The lake makes its own weather. A lid of cloud can sit on the water while Union Station still looks fine. From the observation deck that lid is a white wall at eye level. You will photograph your own reflection. Lake-effect days are the ones people remember as "we went and saw nothing," then they blame the attraction. Blame the lid.

Winter wind

Winter wind off the lake is a plant problem as much as a comfort problem. The outdoor terrace closes. The harness walk outside is often a no. The top pod can lock out when the mast is working harder than the crew wants for a crowd. Inside, the main deck still runs. Fingers on glass still go numb if you came underdressed. The walk from Union in a January northerly is part of the half day. Budget it as such.

When the deck is not worth it

Condition	Call
You cannot read the upper mast from a few blocks away	Do not go up. Haze or cloud is already in charge.
Rain with a low ceiling	The glass floor still works as a pane. The skyline does not.
Severe thunderstorm cells on the lake	Lightning is grounded by the tower; your outdoor plans are not. Wait it out on the ground.
Clear, dry, west light, weekday morning	This is the day the machine earns the walk.

Sunset slots are crowded even on imperfect days because hope is cheap. If the forecast is "mainly clear" and the street says otherwise, trust the street. I did not write this so you would fear weather. I wrote it so you would stop treating a 553-metre observation deck as indoor theatre.