@MsKathleen this is a wooden deck & metal(?) door, or maybe wood/metal overlay. (The deck IMO is not swelling in the cold.)
And yes I am saying water gets in, then freezes & expands, plus expanding everything around it causing things to "stick", and enlarging the leaky area over time as well, sadly.

@MsKathleen I stand by my comment, based on almost 50 years of s8ngl3-handedly caring for a house older than I am, and observing the spaces between the decking on both my front (south-facing) and back (shaded 99% of the time, in all seasons, get Larger in cold weather

@MsKathleen yes,the boards shrink, so the spaces between them get bigger.....why are you trying to pick a fight by repeating everything I said As If I said something else?

Here is how it goes everybody. My wooden porch is large and built way too close to my front door. It is also built on a concrete slab that was not properly put into the ground. In the winter, water gets under that concrete slab and freezes, pushing the slab upwards out of the ground. This was why the door had problems. It hung on the porch deck and would not open. The problem is in the concrete and the way it is put in the ground. The porch itself was not shrinking or swelling.