The only way to deal with rain, wind and cold is layers, layers and layers. Preferably topped off with something that will actually shed water / snow. Getting wet down by your skin is what will really do you in. Quality rain gear is key - somethign way better than a simple poncho - unless it's a really thick one. Keep your hands covered and think about wearing some kind of mask or face gear. Cover as much of your skin as you can - that'll help with the wind as well.