Fuck that, that is a bitch excuse. Do you think the enemy in any case is going to stop and say, "Oh it is cold rainy and slushy out so I will give you a break and not make you run"??? No way that fucker is going to level his gun and plug you in the back of the head if you can't make cover.

There are no breaks in the military, either you pass PT as specified under the available conditions or you keep training until you can. Training is the easy part and when you get out there in the field you will understand why it is the easy part.