I agree with Brad that the problem is in the trap(s). Besides the wind and dried out traps, the vent pipe could be plugged which can cause the traps to be sucked out. If it is safe, go onto the roof and see if leaves or anything else is clogging the vent pipe. Having warm air coming out, this is often a place birds like to nest or even squirrels. I have seen spider webs soaked with condensate that have caused the moisture to freeze and cause a blockage.
If you have never made a mistake, you probably haven't done much.