Well, this is going to be a hard question to answer as there are sooooo many variables. The quick answer to your question is yes you can pour in the cold and in the heat, summer and winter, hot with humidity along with cold and dryness. I pour year around in my garage. My garage in the winter doesn't get any colder than 45 degrees and I live in Illinois. Believe it or not I get better pours in the winter than in summer. I strongly believe that humidity does play a big part in pouring in the summer and I have more problems in the summer. So going back to your question here are some comments and questions I have for you.
***Never ever pour lead out in the open good weather or bad. You must have some shelter over your head all the time. The reason for this is water, rain, rain drop or a splash of water from somewhere. Any kind of liquid near a hot lead pot is an accident waiting to happen. Water and lead even sweat do not mix. If you get water in a hot lead pot, lead will explode all over and burn you.
**You mentioned pouring on the back porch. If you have room , build yourself a makeshift enclosed room out of ply wood, with a roof and walls.You have to keep splashing water away at all costs from the outside.
**If you are going to pour outside, you will need to be sheltered from the wind in the winter, summer is not a problem. If you do not shelter yourself from the wind somehow, your pot will not keep the lead hot.
**Finally you are going to have to have some type of heat source in the winter in your makeshift area. I mentioned earlier that my garage is about 45 degrees on the coldest days. Believe it or not that is cold outside. If it is colder than that, your molds will cool too fast, your pot will not keep up and you body along with your hands will be cold, all the tools you will use will be cold as well. This will cause you to lose focus and your mind will wander on trying to stay warm. Let's face it, you can't pour with insulated gloves and a insulated snowmobile suit dressed like you are going to the antarctic. You will have very little mobility that way.
So in conclusion, you can do anything you want, but safety is #1, and you yourself must stay warm on the coldest of days. Keep water away, get a heat source and try it out. Just an FYI, but these are just my opinions, you can do what you want.