Show Forecasts How do the make their long-range weather WEATHER forecasters study a number of things in determining what the weather will be in a future of the things they watch closest is the build-up and movement of large polar air masses in the polar These air masses spill over and low down over Canada and enter the United They often bring cold or stormy THEIR course can often be If fewer of these polar air masses are or if they seem then it is likely that warm air masses will push upward and over the United States-or at least over a southerly part of |