Dear (имя друга)!
Thanks for your letter. I'm okay, and I hope you too. You asked me, what the weather like is in my city in winter. Well, as you know, Russia is famous for its winters. Usually, in winter it is snowy and freezing cold. At winter my friends and me don't sit at home. We like play at snow a lot! We go ice-skating, skiing and making snowmen. It's so funny!
And what the weather like is in your country? Write me soon.
(Твое имя).