It really depends on where you sit. The lower floors tend to be cooler than the balconies, which can become quite warm as the evening progresses. Also, I've noticed that the temperature warms up and then cools diwn as the air handlers cycle on and off. Usually I sit on the orchestra level and feel fine in a long sleeved flannel dress with either a turtleneck of t-shirt weight, or just a long-sleeved t-shirt under it. Up in the balconies I never wear more than 1 layer, but keep a lightweight scarf over my shoulders until the heat from the audience members takes its inevitable effect.
If you're wearing layers (like a pullover sweater or a cardigan) you'll be fine to a little warm. Without it, you might be a little cold, especially after sitting still for a lengthy show. I'd suggest that you pack that cardigan just in case.
Last time I went was early December. I wore a blazer and was just a little on the warm side.
I am usually cold always. I think temperature is set around 70 degrees.
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