That means it's too cold for the Lincoln Park Zoo's only polar bear, Anana, who was moved to a "climate-controlled" area for her protection.
"She doesn’t typically enjoy the very cold much," a zoo rep Sharon Dewar told DNAinfo Chicago. "Few of us are accustomed to this cold."
Dewar said that the 700-pound Anana hasn't developed the layer of fat blubber that her Arctic cousins use to keep them warm in the winter.
Because of newfound public interest in Anana, the zoo has kept fans up to date on her winter-weather activities on its Facebook page. They noted Tuesday that she'd briefly ventured outside.
"Caregivers report she's explored her outdoor yard a couple times this morning," the zoo said. "She always has the option to stay inside her cozy den, of course!"