The Southern Alps play a significant part in determining New Zealand's weather. The high mountain ranges act like a dam to the wind, forcing weather systems to flow over or around the mountain ranges. The prevailing westerly winds mean the West Coast and mountains have a high rainfall, while the East Coast is baked by a hot dry Nor'wester . When the wind blows from the south, the East Coast receives rain, and snow in winter, while the West Coast will have sunny skys.Southwesterly storms become particularly hard to forecast as a few degrees difference in the storm path is all it takes to have a Nor'wester or Southerly storm. This leads to weather that can change rapidly and forecasts that may evolve during the day. While New Zealand weather forecasts are reasonably reliable they do change over the day. There are special mountain forecasts that should be monitored when travelling in the mountains. Travellers in New Zealand generally, but in the Southern Alps in particular, should be prepared for any type of weather as it is possible to experience four seasons in one day.The Southern Alps also play a significant part in sizing the geography of New Zealand. What would be considered mountains in some other parts of the world are considered mere hills in New Zealand, once compared to the Southern Alps.