The only thing you need to watch out for if pouring concrete during the winter months is the temp.
Rain will have no affect whatsoever on your foundation concrete, as we say in the trade,its hidden work, no one is gonna see it other than a few brickies and ground workers and they will prob have seen a hell of a lot worse.
Once the temp is 3 deg celcius and rising you can pour, 3 deg and falling , don't go there, if you have a pour scheduled for this time of year try and get it started @ roughly 10am so as its finished for lunchtime and should still have 3-5 hours of temperatures above 3 deg, that night cover it with visqueen( polythene sheeting) the heat generated by the curing concrete will therefore be trapped inside the polythene and help cure the concrete and prevent frost cracking occuring.
It does'nt make a blind bit of difference when you start a building, just dont pour any concrete at temperatures below 3 deg, everyone would rather start on a nice spring day with the daffodils blooming all round , but in the real world you have to start when the builder can get to you in most cases.
Best of luck with the foundations Louth man, remember to buy the lads Christmas pints for working in the cold though, it'll get you a lot of work done come new year !!