My older dd started doing the same thing at 15.5-16 months. She'd go "psss" when she had to go pee or poop. I wound up getting a potty and setting it in whatever room she was in and let her run around w/out pants. I was in the same spot in that it was the middle of winter, but she wanted to go, so I figured that I'd take advantage of the opportunity. Within 2 months she was potty trained albeit with quite a few accidents on the floor in that 2 month time when she only recognized the need to go right as she was starting to go. I believe that I took her out on long shopping trips in pull ups until about 19 months or so, though just to be safe.