Bonnie arrived during the bad snow last March. She hated the cold snow. I used to stand with her, umbrella over her (I'd just get cold n wet

) and close the back door. As soon as she was weeing or pooing, I'd dash back to the door and open it for her whilst shouting 'do wee' (cue word) and getting treat ready. She learnt very quickly that wee/poo outside = door opens and she would watch the door whilst squatting ready to dash back inside.
We have said that this actually speeded up the toilet training for her (dry in house from about 12 weeks with only 2\3 wee accidents after that time) because she was rewarded with praise, treats and opening the door. So, use the bad weather to your advantage but keep an umbrella handy for Ralph ( not you

) to keep him dry whilst you are outside. Good luck....it worked for us.