Some times, those SPF pallet tables get hosed with a couple of inches of cold mountain rain.
Then the tables get fried in the morning sun! Other than weathering, I've never noticed any climate induced changes.
Mind you, birch planks out in the open warp, cup and twist like bananas.
Anywhere that the rain/sprinkler/wash water can stand is trouble. Between a support and a deck flat, for example.
I run a wood pellet stove for heat, average 10,000lbs per winter so I get 5 fresh, new, clean freight pallets with that.